JP2008218547A - Piezoelectric body and its driving method, piezoelectric element and device for discharging liquid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric body having an excellent piezoelectric performance, reducing a displacement loss and a power loss and having a superior durability in a long use. <P>SOLUTION: The piezoelectric body has an asymmetric bipolar polarization-electric field hysteresis characteristics having different absolute values of a coercive electric field Ec1 on the negative electric field side and a coercive electric field Ec2 on the positive electric field side, and has characteristics (1-A) or characteristics (1-B). Characteristics (1-A): Ec2>¾Ec1¾ hold, and a bipolar electric field distortion curve has an inflection point in a curve section from an electric field Emax displaying a maximum displacement on the positive electric field side to Ec1. When the electric field at the inflection point is represented by Eif1 Ec1≤0≤Eif1 is satisfied. Characteristics (1-B): Ec2<¾Ec1¾ hold, and the bipolar electric field distortion curve has the inflection point in the curve section from the electric field Emin displaying a maximum displacement on the negative electric field side to Ec2. When the electric field at the inflection point is represented by Eif2, Eif2≤0≤Ec2 is satisfied. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a piezoelectric body made of a ferroelectric material, a driving method thereof, a piezoelectric element using the piezoelectric body, and a liquid discharge apparatus.

  A piezoelectric element including a piezoelectric body made of a ferroelectric material and an electrode for applying an electric field to the piezoelectric body is used as an actuator mounted on an ink jet recording head. As the ferroelectric material, perovskite oxides such as lead zirconate titanate (PZT) are known.

  The characteristics of a piezoelectric material made of a ferroelectric material with respect to electric field change are evaluated by polarization-electric field characteristics (PE characteristics), electric field-strain characteristics, and the like. Hereinafter, although there is a place simply described as a piezoelectric body, it means a piezoelectric body made of a ferroelectric material.

  Non-Patent Document 1 evaluates the characteristics of a c-axis oriented PZT film having a tetragonal crystal structure. 12A and 12B show the polarization-electric field characteristics (FIG. 2) and the voltage-strain characteristics (FIG. 5) of the piezoelectric film described in Non-Patent Document 1. FIG. In this piezoelectric film, the spontaneous polarization axis direction coincides with the electric field application direction, and 180 ° domain inversion occurs but 90 ° domain rotation does not occur. The polarization-electric field characteristic of such a piezoelectric film has a good square shape, and the polarization change sharply occurs in the vicinity of the coercive electric fields Ec1, Ec2. The polarization change in the vicinity of the coercive electric fields Ec1 and Ec2 is due to 180 ° domain inversion. Further, in such a system, only the electric field induced strain that extends in the direction of the spontaneous polarization axis with the increase of the electric field occurs, so the strain changes linearly with respect to the electric field change.

  In a conventional general piezoelectric material, non-180 ° domain rotation such as 90 ° domain rotation occurs, so the polarization change near the coercive electric fields Ec1 and Ec2 is more gradual, and the electric field-strain characteristics show hysteresis. In the conventional general piezoelectric body, the bipolar polarization-electric field curve is substantially symmetric with respect to the y axis (axis indicating the polarization value), and the absolute value of the coercive electric field Ec1 on the negative electric field side and the coercive electric field on the positive electric field side. It substantially coincides with Ec2 (| Ec1 | ≈Ec2). FIG. 13 schematically shows a polarization-electric field curve and an electric field-strain curve of a conventional general piezoelectric material in which non-180 ° domain rotation occurs. The electric field-strain curve is illustrated for bipolar driving and unipolar driving.

  In a normal piezoelectric body, the electric field 0 to the bipolar electric field-strain curve is driven within the range of the electric field Emax that shows the maximum displacement on the positive electric field side. The piezoelectric constant d in the case of driving with 0 ≦ E ≦ Emax corresponds to the slope of the straight line l shown in the bipolar electric field-strain curve and the unipolar electric field-strain curve.

  As shown in FIG. 13, in the conventional piezoelectric body, in the bipolar electric field-strain curve, the area surrounded by ◎ including the range of the coercive electric field Ec1 to 0 on the negative electric field side is an area that can be displaced. Not actively used.

  Patent Document 1 proposes a piezoelectric film that has an asymmetric polarization-electric field hysteresis characteristic, and in which two coercive electric field points in the hysteresis characteristic are positioned at the same electric field polarity (Claim 1). For example, Patent Document 1 describes that a piezoelectric film having the polarization-electric field hysteresis characteristic can be obtained by changing the amount of Zr in the film thickness direction (Claim 3).

  Patent Document 1 describes a polarization-electric field hysteresis curve (FIG. 1) and does not describe an electric field-strain curve. However, the polarization-electric field hysteresis curve and electric field-strain curve of the piezoelectric material described in Patent Document 1 are not described. A schematic representation is as shown in FIG. Here, the case where both the coercive electric fields Ec1 and Ec2 are located on the positive electric field side is illustrated. The bipolar polarization-electric field curve and the bipolar electric field-strain curve shown in FIG. 14 are diagrams in which the bipolar polarization-electric field curve and the bipolar electric field-strain curve shown in FIG. 13 are shifted to the positive electric field side as a whole.

  For comparison, FIG. 15 shows the unipolar electric field-strain curve (solid line) of the piezoelectric body described in Patent Document 1 in FIG. 14 together with the unipolar electric field-strain curve (broken line) in FIG. Here, the shape of the bipolar electric field-strain curve is exactly the same, but the case where Ec1 and Ec2 are shifted is compared.

In the case of driving with 0 ≦ E ≦ Emax, the piezoelectric body having the characteristics shown in FIG. 14 is effectively used even in the region surrounded by ◎ which is not effectively used by the piezoelectric body having the characteristics shown in FIG. Become. As a result, the piezoelectric constant d (corresponding to the slope of the straight line l shown in the bipolar electric field-strain curve and the unipolar electric field-strain curve) when driving with 0 ≦ E ≦ Emax is obtained from the piezoelectric body having the characteristics shown in FIG. Also grows.
JP2003-243741 sensor and actuators A 107 (2003) 68-74 I. Kanno et al.

  When attention is paid to the region surrounded by ◎ in the unipolar electric field-strain curve shown in FIG. 14, when driving with 0 ≦ E ≦ Emax, the displacement is negative at first, and after contracting, it extends. Negative displacement is loss, and the piezoelectric constant d decreases accordingly. This displacement loss is a loss in terms of power because the displacement decreases even if the electric field is increased.

  If attention is paid to the unipolar electric field-strain curve, when driving with 0 ≦ E ≦ Emax, driving is performed through the coercive electric field Ec1, and therefore 180 ° domain inversion (charge inversion) occurs remarkably. The driving condition in which the charge inversion of the piezoelectric body repeatedly occurs is not preferable from the viewpoint of long-term durability.

The present invention has been made in view of the above circumstances, and is excellent in piezoelectric performance, and has less displacement loss and power loss than the piezoelectric body described in Patent Document 1, and excellent in long-term durability. And a driving method thereof.
Another object of the present invention is to provide a piezoelectric element and a liquid ejection apparatus using the piezoelectric body.

The first piezoelectric body of the present invention is made of a ferroelectric material and has coercive electric field points on the negative electric field side and the positive electric field side, respectively, and the absolute value of the coercive electric field Ec1 on the negative electric field side and the resistance on the positive electric field side. In the piezoelectric body having an asymmetric bipolar polarization-electric field hysteresis characteristic different from the electric field Ec2,
It has the following characteristic (1-A) or characteristic (1-B).
Characteristic (1-A): Ec2> | Ec1 |, and the bipolar electric field-strain curve has an inflection point in a curved portion from electric field Emax to Ec1 showing the maximum displacement on the positive electric field side. When the electric field at the bending point is Eif1, Ec1 ≦ 0 ≦ Eif1 is satisfied.
Characteristic (1-B): Ec2 <| Ec1 |, and the bipolar electric field-strain curve has an inflection point in the curved portion from electric field Emin to Ec2 showing the maximum displacement on the negative electric field side. When the electric field at the bending point is Eif2, Eif2 ≦ 0 ≦ Ec2 is satisfied.

The second piezoelectric body of the present invention is made of a ferroelectric material and has coercive electric field points on the negative electric field side and the positive electric field side, respectively, and the absolute value of the coercive electric field Ec1 on the negative electric field side and the resistance on the positive electric field side. In the piezoelectric body having an asymmetric bipolar polarization-electric field hysteresis characteristic different from the electric field Ec2,
It has the following characteristic (2-A) or characteristic (2-B).
Characteristic (2-A): Ec2> | Ec1 |, and when the electric field at which the 180 ° domain inversion starts when the applied electric field is reduced from Ec2 is E180s1, Ec1 ≦ 0 ≦ E180s1 is satisfied.
Characteristic (2-B): Ec2 <| Ec1 |, and E180s2 ≦ 0 ≦ Ec2 is satisfied when E180s2 is an electric field at which 180 ° domain inversion starts when the applied electric field is increased from Ec1.

The third piezoelectric body of the present invention is made of a ferroelectric material and has coercive electric field points on the negative electric field side and the positive electric field side, respectively, and the absolute value of the coercive electric field Ec1 on the negative electric field side and the resistance on the positive electric field side. In the piezoelectric body having an asymmetric bipolar polarization-electric field hysteresis characteristic different from the electric field Ec2,
It has the following characteristic (3-A) or characteristic (3-B).
Characteristic (3-A): Ec2> | Ec1 |, and when the electric field at which the reversal current value starts to increase when the applied electric field is decreased from Ec2 is Eics1 in the reversal current characteristic curve, Ec1 ≦ 0 ≦ Eics1 is satisfied.
Characteristic (3-B): When Ec2 <| Ec1 | and the electric field at which the reversal current value starts to increase when the applied electric field is increased from Ec1 in the reversal current characteristic curve is Eics2, Eics2 ≦ 0 ≦ Ec2 is satisfied.

The fourth piezoelectric body of the present invention is made of a ferroelectric material and has coercive electric field points on the negative electric field side and the positive electric field side, respectively, and the absolute value of the coercive electric field Ec1 on the negative electric field side and the resistance on the positive electric field side. In the piezoelectric body having an asymmetric bipolar polarization-electric field hysteresis characteristic different from the electric field Ec2,
It has the following characteristic (4-A) or characteristic (4-B).
Characteristic (4-A): Ec2> | Ec1 |, and Ec1 ≦ 0 ≦ (3 × Ec1 + 1 × Ec2) / (3 + 1) is satisfied.
Characteristic (4-B): Ec2 <| Ec1 |, and (1 × Ec1 + 3 × Ec2) / (1 + 3) ≦ 0 ≦ Ec2 is satisfied.

A fifth piezoelectric body of the present invention is made of a ferroelectric material, and the bipolar polarization-electric field hysteresis curve has a coercive electric field point on each of a negative electric field side and a positive electric field side.
When the coercive electric field on the negative electric field side and the coercive electric field on the positive electric field side in the bipolar polarization-electric field hysteresis curve are Ec1 and Ec2, respectively, the following characteristic (1-A) is obtained and the following driving condition (i-A) Or the following characteristic (1-B) and driven under the following driving condition (i-B).
Characteristic (1-A): When the bipolar electric field-strain curve has an inflection point in the curve portion from the electric field Emax to Ec1 showing the maximum displacement on the positive electric field side, and the electric field at the inflection point is Eif1. Ec1 ≦ 0 ≦ Eif1 is satisfied.
Driving condition (i-A): Ec1 ≦ Es ≦ Eif1 is satisfied, where Es is the minimum applied electric field for driving.
Characteristic (1-B): When the bipolar electric field-strain curve has an inflection point in a curved portion from electric field Emin to Ec2 showing the maximum displacement on the negative electric field side, and the electric field at the inflection point is Eif2. Eif2 ≦ 0 ≦ Ec2 is satisfied.
Driving condition (i-B): Eif2 ≦ Ee ≦ Ec2 is satisfied, where Ee is the maximum applied electric field for driving.

A sixth piezoelectric body of the present invention is made of a ferroelectric material, and the bipolar polarization-electric field hysteresis curve has a coercive field point on each of a negative electric field side and a positive electric field side.
When the coercive electric field on the negative electric field side and the coercive electric field on the positive electric field side in the bipolar polarization-electric field hysteresis curve are Ec1 and Ec2, respectively, the following characteristic (2-A) is obtained and the following driving condition (ii-A) Or the following characteristic (2-B) and driven under the following driving condition (ii-B).
Characteristic (2-A): Ec1 ≦ 0 ≦ E180s1 is satisfied when the electric field at which the 180 ° domain inversion starts when the applied electric field is decreased from Ec2 is E180s1.
Driving condition (ii-A): When the minimum applied electric field for driving is Es, Ec1 ≦ Es ≦ E180s1 is satisfied.
Characteristic (2-B): E180s2 ≦ 0 ≦ Ec2 is satisfied when the electric field at which the 180 ° domain inversion starts when the applied electric field is increased from Ec1 is E180s2.
Driving condition (ii-B): When the maximum applied electric field for driving is Ee, 180s2 ≦ Ee ≦ Ec2 is satisfied.

A seventh piezoelectric body of the present invention is made of a ferroelectric material, and the bipolar polarization-electric field hysteresis curve has a coercive electric field point on each of a negative electric field side and a positive electric field side.
When the coercive electric field on the negative electric field side and the coercive electric field on the positive electric field side in the bipolar polarization-electric field hysteresis curve are Ec1 and Ec2, respectively, the following characteristic (3-A) is obtained and the following driving condition (iii-A) Or the following characteristic (3-B) and driven under the following driving condition (iii-B).
Characteristic (3-A): In the reversal current characteristic curve, when the electric field at which the reversal current value starts to increase when the applied electric field is decreased from Ec2, Ec1 ≦ 0 ≦ Eics1 is satisfied.
Driving condition (iii-A): When the minimum applied electric field for driving is Es, Ec1 ≦ Es ≦ Eics1 is satisfied.
Characteristic (3-B): In the reversal current characteristic curve, when the electric field at which the reversal current value starts to increase when the applied electric field is increased from Ec1, Eics2 ≦ 0 ≦ Ec2 is satisfied.
Driving condition (iii-B): Eics2 ≦ Ee ≦ Ec2 is satisfied, where Ee is the maximum applied electric field for driving.

The eighth piezoelectric body of the present invention is made of a ferroelectric material, and the bipolar polarization-electric field hysteresis curve has a coercive electric field point on each of the negative electric field side and the positive electric field side.
When the coercive electric field on the negative electric field side and the coercive electric field on the positive electric field side in the bipolar polarization-electric field hysteresis curve are Ec1 and Ec2, respectively, the following characteristic (4-A) is obtained and the following driving condition (iv-A) Or the following characteristic (4-B) and driven under the following driving condition (iv-B).
Characteristic (4-A): Ec1 ≦ 0 ≦ (3 × Ec1 + 1 × Ec2) / (3 + 1) is satisfied.
Driving condition (iv-A): When the minimum applied electric field for driving is Es, Ec1 ≦ Es ≦ (3 × Ec1 + 1 × Ec2) / (3 + 1) is satisfied.
Characteristic (4-B): (1 × Ec1 + 3 × Ec2) / (1 + 3) ≦ 0 ≦ Ec2 is satisfied.
Driving condition (iv−B): When the maximum applied electric field for driving is Ee, (1 × Ec1 + 3 × Ec2) / (1 + 3) ≦ Ee ≦ Ec2 is satisfied.

  The fifth to eighth piezoelectric members of the present invention may have a symmetric or asymmetric bipolar polarization-electric field hysteresis characteristic.

  Usually, the piezoelectric body is used in the form of a piezoelectric element in which a lower electrode, a piezoelectric body, and an upper electrode are sequentially stacked, and one of the lower electrode and the upper electrode is grounded with an applied voltage fixed to 0V. The other electrode is driven as an address electrode whose applied voltage is varied.

  In this specification, “a state where a negative electric field is applied to the piezoelectric body” means that one electrode is a ground electrode whose applied voltage is fixed at 0 V, and the other electrode is an address electrode whose applied voltage is varied. This means a state in which a negative voltage is applied to the address electrodes. Similarly, “a state where a positive electric field is applied to the piezoelectric body” means that one electrode is a ground electrode whose applied voltage is fixed at 0 V, and the other electrode is an address electrode whose applied voltage is varied, It means a state in which a positive voltage is applied to the electrode.

The first to eighth piezoelectric bodies of the present invention are preferably made of one or more perovskite oxides (may contain inevitable impurities). The first to eighth piezoelectric bodies of the present invention are more preferably composed of one or more perovskite oxides (which may contain inevitable impurities) represented by the following general formula (P). preferable.
General formula ABO ₃ (P)
(In the formula, A: an element at the A site, and at least one element selected from the group consisting of Pb, Ba, La, Sr, Bi, Li, Na, Ca, Cd, Mg, and K;
B: Element of B site, Ti, Zr, V, Nb, Ta, Cr, Mo, W, Mn, Sc, Co, Cu, In, Sn, Ga, Zn, Cd, Fe, Ni, and lanthanide element At least one element selected from the group consisting of:
O: oxygen element,
It is standard that the number of moles of the A-site element is 1.0, the number of moles of the B-site element is 1.0, and the number of moles of the oxygen element is 3.0, but these mole numbers are perovskite. It may deviate from the reference number of moles within a range where the structure can be taken. )

  The first to eighth piezoelectric bodies of the present invention are represented by the general formula (P), and the A site is at least one selected from the group consisting of Pb, Ba, Sr, Ca, and Mg. At least one metal element selected from the group consisting of Zr and Ti, and at least one type selected from the group consisting of V, Nb, Ta, Cr, Mo, and W It is particularly preferable to include a perovskite oxide composed of the above metal elements.

  Examples of the first to eighth piezoelectric bodies of the present invention include a piezoelectric film or a piezoelectric ceramic sintered body.

The first to eighth piezoelectric materials of the present invention preferably include a ferroelectric phase having crystal orientation.
In this specification, “having crystal orientation” is defined as an orientation rate F measured by the Lottgering method being 80% or more.
The orientation rate F is represented by the following formula (i).
F (%) = (P−P0) / (1−P0) × 100 (i)
In formula (i), P is the ratio of the total reflection intensity from the orientation plane to the total reflection intensity. In the case of (001) orientation, P is the sum ΣI (00l) of the reflection intensity I (00l) from the (00l) plane and the sum ΣI (hkl) of the reflection intensity I (hkl) from each crystal plane (hkl). ({ΣI (00l) / ΣI (hkl)}). For example, in the case of (001) orientation in the perovskite crystal, P = I (001) / [I (001) + I (100) + I (101) + I (110) + I (111)].
P0 is P of a sample having a completely random orientation.
When the orientation is completely random (P = P0), F = 0%, and when the orientation is complete (P = 1), F = 100%.

  The first to eighth piezoelectric bodies of the present invention preferably include a ferroelectric phase having crystal orientation in a direction different from the spontaneous polarization axis direction.

The ferroelectric phase having crystal orientation in a direction different from the spontaneous polarization axis direction is a rhombohedral phase having crystal orientation in a substantially <100> direction, and a rhombohedral having crystal orientation in a substantially <110> direction. A crystal phase, a tetragonal phase having crystal orientation in a substantially <110> direction, a tetragonal phase having crystal orientation in a substantially <111> direction, an orthorhombic phase having crystal orientation in a substantially <100> direction, and It is preferable that the phase is at least one ferroelectric phase selected from the group consisting of orthorhombic phases having crystal orientation in a substantially <111> direction.
In this specification, “having crystal orientation in the substantially <abc> direction” is defined as the crystal orientation ratio F in that direction being 80% or more.

  The ferroelectric phase having crystal orientation in a direction different from the spontaneous polarization axis direction is such that at least part of the ferroelectric phase is applied by applying an electric field in a direction different from the spontaneous polarization axis direction of the ferroelectric phase. It is preferable that the material has a phase transition property.

The first piezoelectric body driving method of the present invention is a piezoelectric body driving method comprising a ferroelectric material, wherein the bipolar polarization-electric field hysteresis curve has coercive electric field points on the negative electric field side and the positive electric field side, respectively.
When the coercive electric field on the negative electric field side and the coercive electric field on the positive electric field side are respectively Ec1 and Ec2 in the bipolar polarization-electric field hysteresis curve, a piezoelectric body having the following characteristic (1-A) is represented by the following driving condition (i-A). Or a piezoelectric body having the following characteristic (1-B) is driven under the following driving condition (i-B).
Characteristic (1-A): When the bipolar electric field-strain curve has an inflection point in the curve portion from the electric field Emax to Ec1 showing the maximum displacement on the positive electric field side, and the electric field at the inflection point is Eif1. Ec1 ≦ 0 ≦ Eif1 is satisfied.
Driving condition (i-A): Ec1 ≦ Es ≦ Eif1 is satisfied, where Es is the minimum applied electric field for driving.
Characteristic (1-B): When the bipolar electric field-strain curve has an inflection point in a curved portion from electric field Emin to Ec2 showing the maximum displacement on the negative electric field side, and the electric field at the inflection point is Eif2. Eif2 ≦ 0 ≦ Ec2 is satisfied.
Driving condition (i-B): Eif2 ≦ Ee ≦ Ec2 is satisfied, where Ee is the maximum applied electric field for driving.

The second piezoelectric body driving method of the present invention is a piezoelectric body driving method comprising a ferroelectric material, and the bipolar polarization-electric field hysteresis curve has a coercive electric field point on each of a negative electric field side and a positive electric field side.
When the coercive electric field on the negative electric field side and the coercive electric field on the positive electric field side are respectively Ec1 and Ec2 in the bipolar polarization-electric field hysteresis curve, a piezoelectric body having the following characteristic (2-A) is represented by the following driving condition (ii-A). Or a piezoelectric body having the following characteristic (2-B) is driven under the following driving condition (ii-B).
Characteristic (2-A): Ec1 ≦ 0 ≦ E180s1 is satisfied when the electric field at which the 180 ° domain inversion starts when the applied electric field is decreased from Ec2 is E180s1.
Driving condition (ii-A): When the minimum applied electric field for driving is Es, Ec1 ≦ Es ≦ E180s1 is satisfied.
Characteristic (2-B): E180s2 ≦ 0 ≦ Ec2 is satisfied when the electric field at which the 180 ° domain inversion starts when the applied electric field is increased from Ec1 is E180s2.
Driving condition (ii-B): When the maximum applied electric field for driving is Ee, 180s2 ≦ Ee ≦ Ec2 is satisfied.

The third piezoelectric body driving method of the present invention is a piezoelectric body driving method comprising a ferroelectric material, wherein the bipolar polarization-electric field hysteresis curve has a coercive electric field point on each of a negative electric field side and a positive electric field side.
When the coercive electric field on the negative electric field side and the coercive electric field on the positive electric field side in the bipolar polarization-electric field hysteresis curve are Ec1 and Ec2, respectively, a piezoelectric body having the following characteristic (3-A) is represented by the following drive condition (iii-A) Or a piezoelectric body having the following characteristic (3-B) is driven under the following driving condition (iii-B).
Characteristic (3-A): In the reversal current characteristic curve, when the electric field at which the reversal current value starts to increase when the applied electric field is decreased from Ec2, Ec1 ≦ 0 ≦ Eics1 is satisfied.
Driving condition (iii-A): When the minimum applied electric field for driving is Es, Ec1 ≦ Es ≦ Eics1 is satisfied.
Characteristic (3-B): In the reversal current characteristic curve, when the electric field at which the reversal current value starts to increase when the applied electric field is increased from Ec1, Eics2 ≦ 0 ≦ Ec2 is satisfied.
Driving condition (iii-B): Eics2 ≦ Ee ≦ Ec2 is satisfied, where Ee is the maximum applied electric field for driving.

A fourth piezoelectric body driving method of the present invention is a piezoelectric body driving method made of a ferroelectric material, wherein the bipolar polarization-electric field hysteresis curve has coercive electric field points on the negative electric field side and the positive electric field side, respectively.
When the coercive electric field on the negative electric field side and the coercive electric field on the positive electric field side in the bipolar polarization-electric field hysteresis curve are Ec1 and Ec2, respectively, a piezoelectric body having the following characteristic (4-A) is represented by the following driving condition (iv-A). Or a piezoelectric body having the following characteristic (4-B) is driven under the following driving condition (iv-B).
Characteristic (4-A): Ec1 ≦ 0 ≦ (3 × Ec1 + 1 × Ec2) / (3 + 1) is satisfied.
Driving condition (iv-A): When the minimum applied electric field for driving is Es, Ec1 ≦ Es ≦ (3 × Ec1 + 1 × Ec2) / (3 + 1) is satisfied.
Characteristic (4-B): (1 × Ec1 + 3 × Ec2) / (1 + 3) ≦ 0 ≦ Ec2 is satisfied.
Driving condition (iv−B): When the maximum applied electric field for driving is Ee, (1 × Ec1 + 3 × Ec2) / (1 + 3) ≦ Ee ≦ Ec2 is satisfied.

A piezoelectric element according to the present invention includes the above-described piezoelectric body according to the present invention and an electrode that applies an electric field to the piezoelectric body.
The liquid ejection device of the present invention includes the above-described piezoelectric element of the present invention,
A liquid storage chamber in which liquid is stored, and a liquid storage and discharge member having a liquid discharge port through which the liquid is discharged from the liquid storage chamber are provided.

  According to the present invention, it is possible to provide a piezoelectric body excellent in piezoelectric performance and having less displacement loss and power loss and superior long-term durability and a driving method thereof compared with the piezoelectric body described in Patent Document 1. Can do.

"First to fourth piezoelectric bodies of the present invention"
In the “Background Art” section, a conventional general piezoelectric body has a substantially symmetric bipolar polarization-electric field hysteresis characteristic in which the absolute value of the coercive electric field Ec1 on the negative electric field side and the coercive electric field Ec2 on the positive electric field side substantially coincide. (| Ec1 | ≈Ec2, see FIG. 13).

  Patent Document 1 described that a piezoelectric body having an asymmetric bipolar polarization-electric field hysteresis characteristic and having two coercive electric field points in the hysteresis characteristic positioned at the same electric field polarity has been proposed (FIG. 1). 14). In this piezoelectric body, a piezoelectric performance larger than that of the piezoelectric body having the polarization-electric field characteristics shown in FIG. 13 is obtained. However, a negative displacement portion always appears in the unipolar electric field-strain curve, and the displacement loss and the power loss correspond to that portion. Said that In addition, when driving with 0 ≦ E ≦ Emax, it is driven through the coercive electric field Ec1, so that 180 ° domain inversion (charge inversion) occurs remarkably, which is not preferable from the viewpoint of long-term durability. It was.

  In contrast to the conventional piezoelectric body, the first to fourth piezoelectric bodies of the present invention are made of a ferroelectric material and have coercive field points on the negative electric field side and the positive electric field side, respectively. The absolute value of the coercive electric field Ec1 and the coercive electric field Ec2 on the positive electric field side have asymmetric bipolar polarization-electric field hysteresis characteristics (| Ec1 | ≠ Ec2). That is, in the first to fourth piezoelectric bodies of the present invention, the bipolar polarization-electric field hysteresis characteristics are shifted from the symmetry within a range in which the coercive electric field Ec1 and the coercive electric field Ec2 do not have the same electric field polarity.

  In the first to fourth piezoelectric bodies of the present invention, if | Ec1 | ≠ Ec2, the entire bipolar polarization-electric field hysteresis curve is obtained even if Ec2> | Ec1 | in which the entire bipolar polarization-electric field hysteresis curve is biased to the positive electric field side. May be Ec2 <| Ec1 | biased to the negative electric field side.

  Usually, the piezoelectric body is used in the form of a piezoelectric element in which a lower electrode, a piezoelectric body, and an upper electrode are sequentially stacked, and one of the lower electrode and the upper electrode is grounded with an applied voltage fixed to 0V. The other electrode is driven as an address electrode whose applied voltage is varied. In this case, Ec2> | Ec1 | is preferable because it is easier to drive.

  In FIG. 1, in the case of Ec2> | Ec1 |, the polarization-electric field hysteresis curve (PE hysteresis curve), bipolar electric field-strain curve, and unipolar electric field-strain curve of the first to fourth piezoelectric bodies of the present invention. Is shown schematically.

  In the bipolar electric field-strain curve, an electric field showing the maximum displacement on the positive electric field side is Emax, and an electric field showing the maximum displacement on the negative electric field side is Emin. The minimum applied electric field Es and the maximum applied electric field Ee for driving are not particularly limited. When Ec2> | Ec1 |, the first to fourth piezoelectric bodies of the present invention normally set Es to 0 and Ee to Emax or close thereto. Driven as a value.

  For comparison, FIG. 2 shows the unipolar electric field-strain curve (solid line) of FIG. 1 together with the unipolar electric field-strain curve (dashed line) of the piezoelectric material described in Patent Document 1 shown in FIG. deep. Here, the shape of the bipolar electric field-strain curve is exactly the same, but the case where Ec1 and Ec2 are shifted is compared.

  As shown in the unipolar electric field-strain curve of FIG. 2, the first to fourth piezoelectric bodies of the present invention do not pass through the coercive electric field Ec1 on the negative electric field side when driven within the range of 0 ≦ E ≦ Emax. The negative displacement portion of the unipolar electric field-strain curve in the piezoelectric body of Patent Document 1 can be eliminated. Therefore, the first to fourth piezoelectric bodies of the present invention have less displacement loss and power loss than the piezoelectric body described in Patent Document 1, and are excellent in long-term durability. Further, as shown in the figure, in the first to fourth piezoelectric bodies of the present invention, the slope of increase in strain with respect to the increase in electric field when driven within the range of 0 ≦ E ≦ Emax (this slope corresponds to the piezoelectric constant). Is larger than the piezoelectric body of Patent Document 1 and has higher piezoelectric performance than the piezoelectric body of Patent Document 1.

  In the case of Ec2 <| Ec1 |, the polarization-electric field hysteresis curves, bipolar electric field-strain curves, and unipolar electric field-strain curves of the first to fourth piezoelectric bodies of the present invention are obtained by horizontally inverting the curves in FIG. It will be a thing. In FIG. 3, in the case of Ec2 <| Ec1 |, the polarization-electric field hysteresis curve (PE hysteresis curve), bipolar electric field-strain curve, and unipolar electric field-strain curve of the first to fourth piezoelectric bodies of the present invention. Is shown schematically. Also in this case, the minimum applied electric field Es and the maximum applied electric field Ee are not particularly limited, and the first to fourth piezoelectric bodies of the present invention are usually driven with Es set to Emin or a value close thereto, and Ee set to 0. The

<First Piezoelectric Body of the Present Invention>
The first piezoelectric body of the present invention has a coercive electric field point on each of the negative electric field side and the positive electric field side, and the absolute value of the coercive electric field Ec1 on the negative electric field side is different from the coercive electric field Ec2 on the positive electric field side. It has a bipolar polarization-electric field hysteresis characteristic and further has the following characteristic (1-A) or characteristic (1-B).
Characteristic (1-A): Ec2> | Ec1 |, and the bipolar electric field-strain curve has an inflection point in a curved portion from electric field Emax to Ec1 showing the maximum displacement on the positive electric field side. When the electric field at the bending point is Eif1, Ec1 ≦ 0 ≦ Eif1 is satisfied.
Characteristic (1-B): Ec2 <| Ec1 |, and the bipolar electric field-strain curve has an inflection point in the curved portion from electric field Emin to Ec2 showing the maximum displacement on the negative electric field side. When the electric field at the bending point is Eif2, Eif2 ≦ 0 ≦ Ec2 is satisfied.

As shown in FIG. 1, when Ec2> | Ec1 | and the bipolar electric field-strain curve has an inflection point in the curved portion from the electric field Emax to Ec1 showing the maximum displacement on the positive electric field side, 0 ≦ When E ≦ Emax, the slope of the tangent at the inflection point (corresponding to the piezoelectric constant d) is the largest. When a tangent line is drawn with respect to the electric field-strain curve from the point E = Ee, even if Ee is shifted from Emax, the contact always falls within the range of Ec1 to Eif1. Therefore, if Ec1 ≦ 0 ≦ Eif1 is satisfied, the strain displacement gradient (corresponding to the piezoelectric constant d) with respect to the increase in electric field when driven within the range of 0 to Emax can be increased, and a large piezoelectric constant can be obtained. Is obtained.
In the case of Ec2 <| Ec1 |, the same explanation can be made from FIG.

<Second Piezoelectric Body of the Present Invention>
The second piezoelectric body of the present invention has a coercive electric field point on each of the negative electric field side and the positive electric field side, and the absolute value of the coercive electric field Ec1 on the negative electric field side is different from the coercive electric field Ec2 on the positive electric field side. It has a bipolar polarization-electric field hysteresis characteristic and further has the following characteristic (2-A) or characteristic (2-B).
Characteristic (2-A): Ec2> | Ec1 |, and when the electric field at which the 180 ° domain inversion starts when the applied electric field is reduced from Ec2 is E180s1, Ec1 ≦ 0 ≦ E180s1 is satisfied.
Characteristic (2-B): Ec2 <| Ec1 |, and E180s2 ≦ 0 ≦ Ec2 is satisfied when E180s2 is an electric field at which 180 ° domain inversion starts when the applied electric field is increased from Ec1.

  FIG. 4 schematically shows a polarization-electric field hysteresis curve, a bipolar electric field-strain curve (these curves are the same as those in FIG. 1), and an electric field-180 ° domain amount curve in the case of Ec2> | Ec1 |. . Normally, since the lower electrode is driven as a ground electrode and the upper electrode is driven as an address electrode, the 180 ° domain with upward polarization (the 180 ° domain with the + side of polarization being the upper electrode side and the − side of polarization being the lower electrode side) ) Is the ↑ domain, and the 180 ° domain whose polarization is downward (the 180 ° domain where the + side of polarization is the lower electrode side and the − side of polarization is the upper electrode side) is indicated as the ↓ domain. The upward and downward polarization is for convenience.

  In the coercive electric fields Ec1 and Ec2, the amount of the 180 ° domain with upward polarization coincides with the amount of the 180 ° domain with downward polarization, and the polarization P = 0 in the polarization-electric field hysteresis curve.

  In the case of Ec2> | Ec1 |, if the electric field at which the 180 ° domain inversion starts when the applied electric field is decreased from Ec2 is E180s1, and the electric field at which the 180 ° domain inversion is completed is E180e1, between E180s1 and E180e1 The 180 ° domain inversion is noticeable. Since 180 ° domain inversion only changes the vertical direction of the polarization axis, it does not contribute to displacement and is a power loss. If the minimum applied electric field Es for driving is set to E180s1 or more, the inversion from the 180 ° domain in which the polarization is upward to the 180 ° domain in which the polarization is downward does not occur, and power efficiency is good. However, at E <E180s1, non-180 ° domain rotation such as 90 ° domain rotation also occurs. Since non-180 ° domain rotation can be distorted by domain rotation, we want to use it.

Within the range of Ec1 to E180s1, 180 ° domain inversion occurs, but the amount of 180 ° domain inversion is at an acceptable level, and distortion due to non-180 ° domain rotation such as 90 ° domain rotation can also be used. Therefore, if Ec1 ≦ 0 ≦ E180s1 is satisfied, non-180 ° domain rotation such as 90 ° domain rotation while suppressing power loss due to 180 ° domain inversion when driven within the range of 0 ≦ E ≦ Emax. Therefore, a large piezoelectric constant can be obtained.
In the case of Ec2 <| Ec1 |, it can be similarly explained from the left-right reverse view (not shown) of FIG.

<Third Piezoelectric Body of the Present Invention>
The third piezoelectric body of the present invention has coercive electric field points on the negative electric field side and the positive electric field side, respectively, and the absolute value of the coercive electric field Ec1 on the negative electric field side is different from the coercive electric field Ec2 on the positive electric field side. It has bipolar polarization-electric field hysteresis characteristics, and further has the following characteristic (3-A) or characteristic (3-B).
Characteristic (3-A): Ec2> | Ec1 |, and when the electric field at which the reversal current value starts to increase when the applied electric field is decreased from Ec2 is Eics1 in the reversal current characteristic curve, Ec1 ≦ 0 ≦ Eics1 is satisfied.
Characteristic (3-B): When Ec2 <| Ec1 | and the electric field at which the reversal current value starts to increase when the applied electric field is increased from Ec1 in the reversal current characteristic curve is Eics2, Eics2 ≦ 0 ≦ Ec2 is satisfied.

  FIG. 5 schematically shows a polarization-electric field hysteresis curve, a bipolar electric field-strain curve (these curves are the same as those in FIG. 1), and an inversion current characteristic curve in the case of Ec2> | Ec1 |.

  The amount of 180 ° domain inversion can be determined from the inversion current characteristic curve. In the reversal current characteristic curve, the electric field at the peak top of the reversal current peak corresponds to the coercive electric fields Ec1 and Ec2. The reversal current includes those due to non-180 ° domain rotation such as 90 ° domain rotation, but most of the reversal current is due to 180 ° domain reversal, and 180 ° domain reversal is observed from the reversal current curve. An electric field to start and an electric field to end can be determined.

In the case of Ec2> | Ec1 |, the electric field Eics1 in which the reversal current value starts increasing when the applied electric field is decreased from Ec2 is changed to the electric field E180s1 in which the 180 ° domain inversion starts when the applied electric field is decreased from Ec2. Equivalent to. If Ec1 ≦ 0 ≦ Eics1 is satisfied, distortion due to non-180 ° domain rotation, such as 90 ° domain rotation, while suppressing power loss due to 180 ° domain inversion when driven within the range of 0 ≦ E ≦ Emax A large piezoelectric constant can be obtained.
In the case of Ec2 <| Ec1 |, it can be similarly explained from the left-right reverse view (not shown) of FIG.

<Fourth Piezoelectric Body of the Present Invention>
The fourth piezoelectric body of the present invention has coercive electric field points on the negative electric field side and the positive electric field side, respectively, and the absolute value of the coercive electric field Ec1 on the negative electric field side is different from the coercive electric field Ec2 on the positive electric field side. It has a bipolar polarization-electric field hysteresis characteristic, and further has the following characteristic (4-A) or characteristic (4-B).
Characteristic (4-A): Ec2> | Ec1 |, and Ec1 ≦ 0 ≦ (3 × Ec1 + 1 × Ec2) / (3 + 1) is satisfied.
Characteristic (4-B): Ec2 <| Ec1 |, and (1 × Ec1 + 3 × Ec2) / (1 + 3) ≦ 0 ≦ Ec2 is satisfied.

  In the case of Ec2> | Ec1 |, the present inventor has empirically expressed (3 × Ec1 + 1 × Ec2) / (3 + 1) as the electric field E180s1 at which the 180 ° domain inversion starts when the applied electric field is decreased from Ec2. To be found. If Ec1 ≦ 0 ≦ (3 × Ec1 + 1 × Ec2) / (3 + 1) is satisfied, the 90 ° domain is suppressed while suppressing power loss due to 180 ° domain inversion when driven within the range of 0 ≦ E ≦ Emax. Strain due to non-180 ° domain rotation such as rotation can be used, and a large piezoelectric constant can be obtained.

  In the case of Ec2 <| Ec1 |, the present inventor has empirically expressed (1 × Ec1 + 3 × Ec2) / (1 + 3) as the electric field E180s2 where the 180 ° domain inversion starts when the applied electric field is increased from Ec1. To be found. By satisfying (1 × Ec1 + 3 × Ec2) / (1 + 3) ≦ 0 ≦ Ec2, 90 ° domain while suppressing power loss due to 180 ° domain inversion when driven within the range of 0 ≦ E ≦ Emax Strain due to non-180 ° domain rotation such as rotation can be used, and a large piezoelectric constant can be obtained.

  As described above, the first to fourth piezoelectric bodies of the present invention have asymmetric bipolar polarization-electric field hysteresis characteristics in which the absolute value of the coercive electric field Ec1 on the negative electric field side and the coercive electric field Ec2 on the positive electric field side are different. And (1-A), (1-B), (2-A), (2-B), (3-A), (3-B), (4-A), and ( 4-B) satisfying any of the characteristics, the piezoelectric performance is excellent, and displacement loss and power loss are small compared to the piezoelectric body described in Patent Document 1, and long-term use durability is achieved. It will be excellent.

"5th to 8th piezoelectric bodies of the present invention"
In the first to fourth piezoelectric bodies of the present invention, it has been described that when Ec2 <| Ec1 |, it is normally driven within the range of 0 ≦ E ≦ Emax. However, the minimum applied electric field Es and the maximum drive The applied electric field Ee is not particularly limited. In the fifth to eighth piezoelectric bodies of the present invention, the driving conditions are defined together with the polarization-electric field hysteresis characteristics and the like.

  Similarly to the first to fourth piezoelectric bodies of the present invention, the fifth to eighth piezoelectric bodies of the present invention are made of a ferroelectric material, and the bipolar polarization-electric field hysteresis curve has a negative electric field side and a positive electric field side. Each has a coercive electric field point, but the polarization-electric field hysteresis characteristic may be asymmetric or symmetric. Similarly to the first to fourth piezoelectric bodies of the present invention, the coercive electric field on the negative electric field side and the coercive electric field on the positive electric field side in the bipolar polarization-electric field hysteresis curve are Ec1 and Ec2, respectively. In the fifth to eighth piezoelectric bodies of the present invention, | Ec1 | ≠ Ec2 or | Ec1 | = Ec2 may be satisfied.

<Fifth Piezoelectric Body of the Present Invention>
The fifth piezoelectric body of the present invention has the following characteristic (1-A) and is driven under the following driving condition (i-A), or has the following characteristic (1-B), and It is driven under the following driving condition (i-B).
Characteristic (1-A): When the bipolar electric field-strain curve has an inflection point in the curve portion from the electric field Emax to Ec1 showing the maximum displacement on the positive electric field side, and the electric field at the inflection point is Eif1. Ec1 ≦ 0 ≦ Eif1 is satisfied.
Driving condition (i-A): Ec1 ≦ Es ≦ Eif1 is satisfied, where Es is the minimum applied electric field for driving.
Characteristic (1-B): When the bipolar electric field-strain curve has an inflection point in a curved portion from electric field Emin to Ec2 showing the maximum displacement on the negative electric field side, and the electric field at the inflection point is Eif2. Eif2 ≦ 0 ≦ Ec2 is satisfied.
Driving condition (i-B): Eif2 ≦ Ee ≦ Ec2 is satisfied, where Ee is the maximum applied electric field for driving.

  In the fifth piezoelectric body of the present invention, when Ec2> | Ec1 |, the minimum applied electric field Es for driving is defined in the first piezoelectric body of the present invention, and in the case of Ec2 <| Ec1 | The maximum applied electric field Ee for driving in the first piezoelectric body of the present invention is defined.

  In the above first piezoelectric body of the present invention, when Ec2> | Ec1 |, the minimum applied electric field Es = 0 for driving and the maximum applied electric field Ee = Emax for driving are basically described. Es may be shifted from zero. If Ec1 ≦ Es ≦ Eif1 is satisfied, the slope of the strain displacement (corresponding to the piezoelectric constant d) with respect to the increase in electric field when driven can be increased, and a large piezoelectric constant can be obtained (the first aspect of the present invention). 1 and the description of FIG. 1).

  The above driving conditions are also suitable when Ec2 = | Ec1 |. FIG. 6 shows a polarization-electric field hysteresis curve and an electric field-strain curve when the polarization-electric field hysteresis characteristics are symmetric. When the polarization-electric field hysteresis characteristic is symmetric, the piezoelectric constant increases, and therefore Es <0 (a bias voltage is applied) is particularly preferable.

The above driving conditions are also suitable when Ec2 <| Ec1 |.
In the drive start electric field, the domain in which the polarization is upward (the domain where the + side of polarization is the upper electrode side and the − side of the polarization is the lower electrode side) is the domain where the polarization is downward (the − side of the polarization is the upper electrode side, If the condition is larger than the domain in which the + side of polarization is on the lower electrode side), it is preferable to drive under the driving condition (i-A).
Conversely, in the drive start electric field, the domain in which the polarization is downward (the domain in which the negative side of the polarization is the upper electrode side and the positive side of the polarization is the lower electrode side) is the domain in which the polarization is upward (the positive side of the polarization is on the upper electrode side). It is preferable that the driving is performed under the driving condition (i-B) if there are more conditions than the domain in which the negative side of polarization is the lower electrode side.

<Sixth Piezoelectric Body of the Present Invention>
The sixth piezoelectric body of the present invention has the following characteristic (2-A) and is driven under the following driving condition (ii-A), or has the following characteristic (2-B), and It is driven under the following drive condition (ii-B).
Characteristic (2-A): Ec1 ≦ 0 ≦ E180s1 is satisfied when the electric field at which the 180 ° domain inversion starts when the applied electric field is decreased from Ec2 is E180s1.
Driving condition (ii-A): When the minimum applied electric field for driving is Es, Ec1 ≦ Es ≦ E180s1 is satisfied.
Characteristic (2-B): E180s2 ≦ 0 ≦ Ec2 is satisfied when the electric field at which the 180 ° domain inversion starts when the applied electric field is increased from Ec1 is E180s2.
Driving condition (ii-B): When the maximum applied electric field for driving is Ee, 180s2 ≦ Ee ≦ Ec2 is satisfied.

  In the sixth piezoelectric body of the present invention, when Ec2> | Ec1 |, the minimum applied electric field Es for driving is defined in the second piezoelectric body of the present invention, and when Ec2 <| Ec1 | The maximum applied electric field Ee for driving in the second piezoelectric body of the present invention is defined.

  In the second piezoelectric body of the present invention, when Ec2> | Ec1 |, the minimum applied electric field Es = 0 for driving and the maximum applied electric field Ee = Emax for driving are basically described. Es may be shifted from zero. If Ec1 ≦ Es ≦ E180s1 is satisfied, distortion due to non-180 ° domain rotation such as 90 ° domain rotation can be used while suppressing power loss due to 180 ° domain inversion, and a large piezoelectric constant can be obtained (see above book). (See description of the second piezoelectric body of the invention and FIG. 4).

  The above driving conditions are also suitable when Ec2 = | Ec1 |. FIG. 7 shows a polarization-electric field hysteresis curve and an electric field-strain curve when the polarization-electric field hysteresis characteristics are symmetric. When the polarization-electric field hysteresis characteristic is symmetric, the piezoelectric constant increases, and therefore Es <0 (a bias voltage is applied) is particularly preferable.

The above driving conditions are also suitable when Ec2 <| Ec1 |.
In the drive start electric field, the domain in which the polarization is upward (the domain where the + side of polarization is the upper electrode side and the − side of the polarization is the lower electrode side) is the domain where the polarization is downward (the − side of the polarization is the upper electrode side, If the condition is larger than the domain in which the + side of polarization is on the lower electrode side), the driving is preferably performed under the driving condition (ii-A).
Conversely, in the drive start electric field, the domain in which the polarization is downward (the domain in which the negative side of the polarization is the upper electrode side and the positive side of the polarization is the lower electrode side) is the domain in which the polarization is upward (the positive side of the polarization is on the upper electrode side). It is preferable that the driving is performed under the driving condition (ii-B) if there are more conditions than the domain in which the negative side of polarization is the lower electrode side.

<Seventh Piezoelectric Body of the Present Invention>
The seventh piezoelectric body of the present invention has the following characteristic (3-A) and is driven under the following driving condition (iii-A), or has the following characteristic (3-B), and It is driven under the following driving condition (iii-B).
Characteristic (3-A): In the reversal current characteristic curve, when the electric field at which the reversal current value starts to increase when the applied electric field is decreased from Ec2, Ec1 ≦ 0 ≦ Eics1 is satisfied.
Driving condition (iii-A): When the minimum applied electric field for driving is Es, Ec1 ≦ Es ≦ Eics1 is satisfied.
Characteristic (3-B): In the reversal current characteristic curve, when the electric field at which the reversal current value starts to increase when the applied electric field is increased from Ec1, Eics2 ≦ 0 ≦ Ec2 is satisfied.
Driving condition (iii-B): Eics2 ≦ Ee ≦ Ec2 is satisfied, where Ee is the maximum applied electric field for driving.

  In the seventh piezoelectric body of the present invention, when Ec2> | Ec1 |, the minimum applied electric field Es for driving is defined in the third piezoelectric body of the present invention, and when Ec2 <| Ec1 | The maximum applied electric field Ee for driving in the third piezoelectric body of the present invention is defined.

  In the third piezoelectric body of the present invention, when Ec2> | Ec1 |, the minimum applied electric field Es = 0 for driving and the maximum applied electric field Ee = Emax for driving are basically described. Es may be shifted from zero. If Ec1 ≦ Es ≦ Eics1 is satisfied, distortion due to non-180 ° domain rotation such as 90 ° domain rotation can be used while suppressing power loss due to 180 ° domain inversion, and a large piezoelectric constant can be obtained (see above book). (See description of the third piezoelectric body of the invention and FIG. 5).

  The above driving conditions are also suitable when Ec2 = | Ec1 |. When the polarization-electric field hysteresis characteristic is symmetric, the piezoelectric constant increases, and therefore Es <0 (a bias voltage is applied) is particularly preferable.

The above driving conditions are also suitable when Ec2 <| Ec1 |.
In the drive start electric field, the domain in which the polarization is upward (the domain where the + side of polarization is the upper electrode side and the − side of the polarization is the lower electrode side) is the domain where the polarization is downward (the − side of the polarization is the upper electrode side, If the condition is larger than the domain in which the + side of polarization is on the lower electrode side), it is preferable to drive under the driving condition (iii-A).
Conversely, in the drive start electric field, the domain in which the polarization is downward (the domain in which the negative side of the polarization is the upper electrode side and the positive side of the polarization is the lower electrode side) is the domain in which the polarization is upward (the positive side of the polarization is on the upper electrode side). If the condition is larger than the domain in which the negative side of polarization is the lower electrode side), it is preferable to drive under the driving condition (iii-B).

<Eighth Piezoelectric Body of the Present Invention>
The eighth piezoelectric body of the present invention has the following characteristic (4-A) and is driven under the following driving condition (iv-A), or has the following characteristic (4-B), and It is driven under the following drive condition (iv-B).
Characteristic (4-A): Ec1 ≦ 0 ≦ (3 × Ec1 + 1 × Ec2) / (3 + 1) is satisfied.
Driving condition (iv-A): When the minimum applied electric field for driving is Es, Ec1 ≦ Es ≦ (3 × Ec1 + 1 × Ec2) / (3 + 1) is satisfied.
Characteristic (4-B): (1 × Ec1 + 3 × Ec2) / (1 + 3) ≦ 0 ≦ Ec2 is satisfied.
Driving condition (iv−B): When the maximum applied electric field for driving is Ee, (1 × Ec1 + 3 × Ec2) / (1 + 3) ≦ Ee ≦ Ec2 is satisfied.

  In the eighth piezoelectric body of the present invention, when Ec2> | Ec1 |, the minimum applied electric field Es for driving is defined in the fourth piezoelectric body of the present invention, and when Ec2 <| Ec1 | The maximum applied electric field Ee for driving is defined in the fourth piezoelectric body of the present invention.

  In the fourth piezoelectric body of the present invention, when Ec2> | Ec1 |, the minimum applied electric field Es = 0 for driving and the maximum applied electric field Ee = Emax for driving are basically described. Es may be shifted from zero. If Ec1 ≦ Es ≦ (3 × Ec1 + 1 × Ec2) / (3 + 1) is satisfied, distortion due to non-180 ° domain rotation such as 90 ° domain rotation can be used while suppressing power loss due to 180 ° domain inversion. A large piezoelectric constant can be obtained (see the description of the fourth piezoelectric body of the present invention above).

  The above driving conditions are also suitable when Ec2 = | Ec1 |. When the polarization-electric field hysteresis characteristic is symmetric, the piezoelectric constant increases, and therefore Es <0 (a bias voltage is applied) is particularly preferable.

The above driving conditions are also suitable when Ec2 <| Ec1 |.
In the drive start electric field, the domain in which the polarization is upward (the domain where the + side of polarization is the upper electrode side and the − side of the polarization is the lower electrode side) is the domain where the polarization is downward (the − side of the polarization is the upper electrode side, If the condition is larger than the domain in which the + side of polarization is on the lower electrode side), it is preferable to drive under the driving condition (iv-A).
Conversely, in the drive start electric field, the domain in which the polarization is downward (the domain in which the negative side of the polarization is the upper electrode side and the positive side of the polarization is the lower electrode side) is the domain in which the polarization is upward (the positive side of the polarization is on the upper electrode side). It is preferable that the driving is performed under the driving condition (iv-B) if there are more conditions than the domain in which the negative side of polarization is the lower electrode side.

  As described above, since the fifth to eighth piezoelectric bodies of the present invention define the polarization-electric field characteristics, the electric field-strain characteristics, and the driving conditions, the piezoelectric performance is excellent, and Patent Document 1 Compared with the piezoelectric body described in 1), the displacement loss and power loss are small, and the long-term durability is excellent.

“Compositions of First to Eighth Piezoelectric Elements of the Present Invention”
The composition of the first to eighth piezoelectric bodies of the present invention is not particularly limited as long as it is a composition made of a ferroelectric material.

The first to eighth piezoelectric bodies of the present invention are preferably composed of one or more perovskite oxides (may contain inevitable impurities). The first to eighth piezoelectric bodies of the present invention are more preferably composed of one or more perovskite oxides (which may contain inevitable impurities) represented by the following general formula (P). .
General formula ABO ₃ (P)
(In the formula, A: an element at the A site, and at least one element selected from the group consisting of Pb, Ba, La, Sr, Bi, Li, Na, Ca, Cd, Mg, and K;
B: Element of B site, Ti, Zr, V, Nb, Ta, Cr, Mo, W, Mn, Sc, Co, Cu, In, Sn, Ga, Zn, Cd, Fe, Ni, and lanthanide element At least one element selected from the group consisting of:
O: oxygen element,
It is standard that the number of moles of the A-site element is 1.0, the number of moles of the B-site element is 1.0, and the number of moles of the oxygen element is 3.0, but these mole numbers are perovskite. It may deviate from the reference number of moles within a range where the structure can be taken. )

As the perovskite oxide represented by the general formula (P),
Lead titanate, lead zirconate titanate (PZT), lead zirconate, lead lanthanum titanate, lead lanthanum zirconate titanate, lead zirconium niobate titanate titanate, lead niobium zirconium titanate titanate, titanium titanate zinc niobate Lead-containing compounds such as lead acid, and mixed crystal systems thereof;
Examples thereof include lead-free compounds such as barium titanate, barium strontium titanate, bismuth sodium titanate, bismuth potassium titanate, sodium niobate, potassium niobate, lithium niobate, and mixed crystal systems thereof.

  Since the electrical characteristics become better, the first to eighth piezoelectric bodies of the present invention have Mg, Ca, Sr, Ba, Bi, Nb, Ta, W, and Ln (= lanthanide elements (La, Ce, It is preferable to contain one or more metal ions such as Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu)).

  The first to eighth piezoelectric bodies of the present invention are represented by the general formula (P), and the A site is at least one selected from the group consisting of Pb, Ba, Sr, Ca, and Mg. At least one metal element selected from the group consisting of metal elements, and B site is selected from the group consisting of Zr and Ti, and at least one kind selected from the group consisting of V, Nb, Ta, Cr, Mo, and W It is preferable to include a perovskite oxide composed of a metal element. In this perovskite oxide, part of the B site of a 2-4 perovskite oxide (PZT, etc.) in which the A site is divalent and the B site is tetravalent is selected from the group of elements of the V group and the VI group And at least one kind of metal element. With the perovskite oxide having such a composition, it is easy to realize the polarization-electric field hysteresis characteristics and electric field-strain characteristics of the first to eighth piezoelectric materials of the present invention (see Examples below). It is considered that the space charge is generated in the crystal lattice by the substitution element, and the hysteresis property of the polarization-electric field characteristic can be adjusted. For example, the present inventor has found that the polarization-electric field characteristics have a good square shape in non-doped PZT, but the polarization-electric field characteristics become asymmetric hysteresis by doping Nb. Furthermore, the hysteresis property of the polarization-electric field characteristics can be adjusted by changing the doping amount of the substitution element selected from the group V and group VI elements in the thickness direction of the piezoelectric body.

The space charge can be introduced by intentionally providing A site defects or oxygen defects in addition to doping the B site with a metal element having a large valence.
The hysteresis property of the polarization-electric field characteristics can be adjusted by the crystal orientation of the piezoelectric body, the composition of the seed layer and / or the crystal orientation.

"Crystal structure of first to eighth piezoelectric bodies of the present invention"
The first to eighth piezoelectric materials of the present invention preferably include a ferroelectric phase having crystal orientation.

For piezoelectric strain,
(1) Normal piezoelectric strain (electric field induced strain) that expands and contracts in the electric field application direction by increasing or decreasing the electric field application intensity when the vector component of the spontaneous polarization axis coincides with the electric field application direction,
(2) Piezoelectric strain generated by reversibly rotating the polarization axis by non-180 ° by increasing or decreasing the electric field applied intensity,
(3) Piezoelectric strain that uses a volume change due to phase transition by changing the phase of the crystal by increasing or decreasing the electric field applied intensity,
(4) Larger strain can be obtained by using a material that has the property of phase transition upon application of an electric field and having a crystalline orientation structure that includes a ferroelectric phase having crystal orientation in a direction different from the direction of the spontaneous polarization axis. Piezoelectric strain using engineered domain effect (when engineered domain effect is used, it may be driven under conditions where phase transition occurs, or it may be driven within a range where phase transition does not occur) It is done.

  (2) Piezoelectric strain using reversible non-180 ° domain rotation is described in JP-A-2004-363557 and the like. (3) Piezoelectric strain utilizing phase transition is described in Japanese Patent No. 3568107. (4) Regarding the engineered domain effect and piezoelectric strain using the same, “Ultra high strain and piezoelectric behavior in relaxor based ferroelectric single crystals”, SEPark et.al., JAP, 82, 1804 (1997), the present applicant. Is described in Japanese Patent Application No. 2006-188765 filed earlier (unpublished at the time of filing this application).

  A desired piezoelectric strain can be obtained by using the piezoelectric strains (1) to (4) singly or in combination. In addition, any of the above piezoelectric strains (1) to (4) can have a larger piezoelectric strain by adopting a crystal orientation structure corresponding to the principle of strain generation.

  The inventor has found that the polarization-electric field characteristics and the electric field-strain characteristics of the first to eighth piezoelectric bodies of the present invention can be easily realized by adopting the engineered domain structure (4).

  The engineered domain system described in Japanese Patent Application No. 2006-188765 will be described below. In this system, the piezoelectric body is configured to include a ferroelectric phase having a property of phase transition to another ferroelectric phase having a different crystal system by applying an electric field.

  In order to simplify the explanation, the piezoelectric characteristics of the piezoelectric body composed only of the ferroelectric phase having the property of phase transition to another ferroelectric phase having a different crystal system when an electric field is applied will be described. FIG. 8 schematically shows the relationship between the electric field strength of the piezoelectric body and the amount of strain displacement.

  In FIG. 8, the electric field strength E1 is the minimum electric field strength at which the phase transition of the ferroelectric phase starts. The electric field strength E2 is an electric field strength at which the phase transition of the ferroelectric phase is almost completely completed. Usually E1 <E2, but E1 = E2 is also possible. “The electric field intensity E2 at which the phase transition is almost completely completed” means an electric field intensity at which no further phase transition occurs even when an electric field is applied further. Even when an electric field strength of E2 or higher is applied, a part of the ferroelectric phase may remain without phase transition.

  As shown in FIG. 8, in the piezoelectric body, when 0 ≦ E ≦ E1 (before the phase transition), the strain displacement amount linearly increases as the electric field strength increases due to the piezoelectric effect of the ferroelectric phase before the phase transition. When E1 ≦ E ≦ E2, the volume change occurs due to the change of the crystal structure accompanying the phase transition, the strain displacement increases linearly with the increase of the electric field strength, and when E ≧ E2 (after the phase transition) Due to the piezoelectric effect of the ferroelectric phase after the phase transition, it has a piezoelectric characteristic in which the amount of strain displacement increases linearly as the electric field strength increases.

  In the piezoelectric body, a volume change (range of electric field strength E = E1 to E2) occurs due to a change in crystal structure accompanying the phase transition, and the piezoelectric body is made of a ferroelectric material before and after the phase transition. The piezoelectric effect of the ferroelectric material can be obtained before and after the transition, and a large strain displacement amount can be obtained in any of the electric field strengths E = 0 to E1, E = E1 to E2, and E ≧ E2.

The driving condition of the piezoelectric body is not limited, and it is preferable that the minimum electric field strength Es and the maximum electric field intensity Ee are driven under the conditions satisfying the following formula (X) in consideration of the strain displacement amount. It is particularly preferable that the motor is driven under a condition that satisfies the above.
Es <E1 <Ee (X),
Es <E1 ≦ E2 <Ee (Y)

  In the electric field induced phase transition system, the ferroelectric phase in which the phase transition occurs preferably has a crystal orientation in a direction different from the spontaneous polarization axis direction, and the spontaneous polarization axis direction after the phase transition and It is particularly preferable to have crystal orientation in a substantially coincident direction. Usually, the crystal orientation direction is the electric field application direction.

  When the electric field application direction is made to substantially coincide with the spontaneous polarization axis direction after the phase transition, the “engineered domain effect” before the phase transition is larger than matching the electric field application direction with the spontaneous polarization axis direction before the phase transition. A displacement amount is obtained, which is preferable. The engineered domain effect of single crystals is described in “Ultra high strain and piezoelectric behavior in relaxor based ferroelectric single crystals”, S.E. Park et.al., JAP, 82, 1804 (1997).

  Further, the phase transition is likely to occur by making the electric field application direction substantially coincide with the spontaneous polarization axis direction after the phase transition. This is presumably because the direction in which the spontaneous polarization axis direction matches the direction of electric field application is crystallographically stable, and phase transition to a more stable crystal system is facilitated. Even if an electric field of electric field strength E2 or more is applied, a part of the ferroelectric phase may remain without phase transition, but an electric field of electric field strength E2 or more was applied because the phase transition proceeded efficiently. In this case, the proportion of the ferroelectric phase remaining without phase transition can be reduced. As a result, a larger strain displacement can be stably obtained than when the electric field application direction is matched with the spontaneous polarization axis direction before the phase transition.

  Furthermore, after the phase transition, the electric field application direction and the spontaneous polarization axis direction substantially coincide with each other, so that the piezoelectric effect of the ferroelectric phase after the phase transition is effectively expressed, and a large strain displacement is stable. Is obtained.

  As described above, when the electric field application direction is substantially coincident with the spontaneous polarization axis direction after the phase transition, a high strain displacement can be obtained before, during, and after the phase transition. This effect is obtained if the direction of spontaneous polarization axis of the ferroelectric phase before the phase transition is different from the direction of electric field application, and the direction of electric field application is close to the direction of the spontaneous polarization axis of the ferroelectric phase after phase transition. It appears more remarkably.

  That is, the first to eighth piezoelectric bodies of the present invention preferably include a ferroelectric phase having crystal orientation in a direction different from the spontaneous polarization axis direction.

The ferroelectric phase having crystal orientation in a direction different from the spontaneous polarization axis direction is a rhombohedral phase having crystal orientation in a substantially <100> direction, and a rhombohedral crystal having crystal orientation in a substantially <110> direction. A tetragonal phase having crystal orientation in a substantially <110> direction, a tetragonal phase having crystal orientation in a substantially <111> direction, an orthorhombic phase having crystal orientation in a substantially <100> direction, and a substantially It is preferably at least one ferroelectric phase selected from the group consisting of orthorhombic phases having crystal orientation in the <111> direction.
In the ferroelectric phase having crystal orientation in a direction different from the spontaneous polarization axis direction, at least a part of the ferroelectric phase undergoes phase transition by applying an electric field in a direction different from the spontaneous polarization axis direction of the ferroelectric phase. It is preferable that it has a property.

“Forms of First to Eighth Piezoelectric Elements of the Present Invention”
The forms of the first to eighth piezoelectric bodies of the present invention are appropriately designed and may be a piezoelectric film or a piezoelectric ceramic sintered body. In applications such as an ink jet recording head, increasing the density of piezoelectric elements has been studied in order to improve image quality, and accordingly, reducing the thickness of piezoelectric elements has been studied. In consideration of thinning of the piezoelectric element, a piezoelectric film is preferable as the piezoelectric body, and a piezoelectric thin film having a thickness of 20 μm or less is more preferable. Since the first to eighth piezoelectric bodies of the present invention have high piezoelectric performance, they are effective for thin films that require higher piezoelectric constants.

"Piezoelectric element and inkjet recording head"
With reference to the drawings, the structure of a piezoelectric element according to an embodiment of the present invention and an ink jet recording head (liquid ejecting apparatus) including the same will be described. FIG. 9 is a sectional view (a sectional view in the thickness direction of the piezoelectric element) of the ink jet recording head. In order to facilitate visual recognition, the scale of the constituent elements is appropriately changed from the actual one.

  The piezoelectric element 1 shown in FIG. 9 is an element in which a lower electrode 12, a piezoelectric body 13, and an upper electrode 14 are sequentially laminated on the surface of a substrate 11. The piezoelectric body 13 is one of the first to eighth piezoelectric bodies of the present invention, and an electric field is applied in the thickness direction by the lower electrode 12 and the upper electrode 14.

The substrate 11 is not particularly limited, and examples thereof include silicon, glass, stainless steel (SUS), yttrium stabilized zirconia (YSZ), alumina, sapphire, and silicon carbide. As the substrate 11, a laminated substrate such as an SOI substrate in which a SiO ₂ film and a Si active layer are sequentially laminated on a silicon substrate may be used.

The main component of the lower electrode 12 is not particularly limited, and examples thereof include metals or metal oxides such as Au, Pt, Ir, IrO ₂ , RuO ₂ , LaNiO ₃ , and SrRuO ₃ , and combinations thereof. The main component of the upper electrode 14 is not particularly limited, and examples thereof include materials exemplified for the lower electrode 20, electrode materials generally used in semiconductor processes such as Al, Ta, Cr, and Cu, and combinations thereof. The thicknesses of the lower electrode 12 and the upper electrode 14 are not particularly limited and are preferably 50 to 500 nm.

In the piezoelectric actuator 2, a vibration plate 16 that vibrates due to expansion and contraction of the piezoelectric body 14 is attached to the back surface of the substrate 11 of the piezoelectric element 1. The piezoelectric actuator 2 is also provided with a control means 15 such as a drive circuit for controlling the driving of the piezoelectric element 1. The ink jet recording head (liquid ejecting apparatus) 3 is roughly composed of an ink chamber (liquid storing chamber) 21 in which ink is stored on the back surface of the piezoelectric actuator 2 and an ink discharging port (in which ink is discharged from the ink chamber 21 to the outside). An ink nozzle (liquid storage and discharge member) 20 having a liquid discharge port 22 is attached.
In the ink jet recording head 3, the electric field strength applied to the piezoelectric element 1 is increased / decreased to expand / contract the piezoelectric element 1, thereby controlling the ejection of the ink from the ink chamber 21 and the ejection amount.

  Instead of attaching the diaphragm 16 and the ink nozzle 20 which are members independent of the substrate 11, a part of the substrate 11 may be processed into the diaphragm 16 and the ink nozzle 20. For example, when the substrate 11 is made of a laminated substrate such as an SOI substrate, the substrate 11 is etched from the back side to form the ink chamber 21, and the diaphragm 16 and the ink nozzle 20 are formed by processing the substrate itself. Can do.

  Since the piezoelectric element 1 includes the piezoelectric body 13 made of any one of the first to eighth piezoelectric bodies of the present invention, the piezoelectric element 1 is excellent in piezoelectric performance, has little displacement loss and power loss, and has long-term use durability. It will be excellent.

"Inkjet recording device"
With reference to FIGS. 10 and 11, a configuration example of an ink jet recording apparatus including the ink jet recording head 3 according to the above embodiment will be described. FIG. 10 is an overall view of the apparatus, and FIG. 11 is a partial top view.

  The illustrated ink jet recording apparatus 100 includes a printing unit 102 having a plurality of ink jet recording heads (hereinafter simply referred to as “heads”) 3K, 3C, 3M, and 3Y provided for each ink color, and each head 3K, An ink storage / loading unit 114 that stores ink to be supplied to 3C, 3M, and 3Y, a paper feeding unit 118 that supplies recording paper 116, a decurling unit 120 that removes curling of the recording paper 116, and a printing unit An adsorption belt conveyance unit 122 that conveys the recording paper 116 while maintaining the flatness of the recording paper 116, and a print detection unit that reads a printing result by the printing unit 102. 124 and a paper discharge unit 126 that discharges printed recording paper (printed matter) to the outside.

  Each of the heads 3K, 3C, 3M, and 3Y forming the printing unit 102 is the ink jet recording head 3 of the above embodiment.

In the decurling unit 120, heat is applied to the recording paper 116 by the heating drum 130 in the direction opposite to the curl direction, and the decurling process is performed.
In the apparatus using roll paper, as shown in FIG. 10, a cutter 128 is provided at the subsequent stage of the decurling unit 120, and the roll paper is cut into a desired size by this cutter. The cutter 128 includes a fixed blade 128A having a length equal to or larger than the conveyance path width of the recording paper 116, and a round blade 128B that moves along the fixed blade 128A. The fixed blade 128A is provided on the back side of the print. The round blade 128B is arranged on the print surface side with the conveyance path interposed therebetween. In an apparatus using cut paper, the cutter 128 is unnecessary.

  The decurled and cut recording paper 116 is sent to the suction belt conveyance unit 122. The suction belt conveyance unit 122 has a structure in which an endless belt 133 is wound between rollers 131 and 132, and at least portions facing the nozzle surface of the printing unit 102 and the sensor surface of the printing detection unit 124 are horizontal ( Flat surface).

  The belt 133 has a width that is wider than the width of the recording paper 116, and a plurality of suction holes (not shown) are formed on the belt surface. An adsorption chamber 134 is provided at a position facing the nozzle surface of the printing unit 102 and the sensor surface of the print detection unit 124 inside the belt 133 that is stretched between the rollers 131 and 132. The recording paper 116 on the belt 133 is sucked and held by suctioning at 135 to make a negative pressure.

  The power of a motor (not shown) is transmitted to at least one of the rollers 131 and 132 around which the belt 133 is wound, so that the belt 133 is driven in the clockwise direction in FIG. 10 and held on the belt 133. The recording paper 116 is conveyed from left to right in FIG.

Since ink adheres to the belt 133 when a borderless print or the like is printed, the belt cleaning unit 136 is provided at a predetermined position outside the belt 133 (an appropriate position other than the print region).
A heating fan 140 is provided on the upstream side of the printing unit 102 on the paper conveyance path formed by the suction belt conveyance unit 122. The heating fan 140 heats the recording paper 116 by blowing heated air onto the recording paper 116 before printing. Heating the recording paper 116 immediately before printing makes it easier for the ink to dry after landing.

  The printing unit 102 is a so-called full line type head in which line type heads having a length corresponding to the maximum paper width are arranged in a direction (main scanning direction) orthogonal to the paper feed direction (see FIG. 11). Each of the print heads 3K, 3C, 3M, and 3Y is a line-type head in which a plurality of ink discharge ports (nozzles) are arranged over a length exceeding at least one side of the maximum-size recording paper 116 targeted by the ink jet recording apparatus 100. It is configured.

  Heads 3K, 3C, 3M, and 3Y corresponding to the respective color inks are arranged in the order of black (K), cyan (C), magenta (M), and yellow (Y) from the upstream side along the feeding direction of the recording paper 116. ing. A color image is recorded on the recording paper 116 by ejecting the color ink from each of the heads 3K, 3C, 3M, 3Y while conveying the recording paper 116.

The print detection unit 124 includes a line sensor that images the droplet ejection result of the print unit 102 and detects ejection defects such as nozzle clogging from the droplet ejection image read by the line sensor.
A post-drying unit 142 including a heating fan or the like for drying the printed image surface is provided at the subsequent stage of the print detection unit 124. Since it is preferable to avoid contact with the printing surface until the ink after printing is dried, a method of blowing hot air is preferred.

  A heating / pressurizing unit 144 is provided downstream of the post-drying unit 142 in order to control the glossiness of the image surface. The heating / pressurizing unit 144 presses the image surface with a pressure roller 145 having a predetermined surface irregularity shape while heating the image surface, and transfers the irregular shape to the image surface.

The printed matter obtained in this manner is outputted from the paper output unit 126. It is preferable that the original image to be printed (printed target image) and the test print are discharged separately. In the ink jet recording apparatus 100, there is provided sorting means (not shown) for switching the paper discharge path in order to select the print product of the main image and the print product of the test print and send them to the discharge units 126A and 126B. It has been.
When the main image and the test print are simultaneously printed on a large sheet of paper, the cutter 148 may be provided to separate the test print portion.
The ink jet recording apparatus 100 is configured as described above.

  Examples and comparative examples according to the present invention will be described.

(Example 1)
A lower electrode having a laminated structure of a 20 nm thick Ti layer and a 260 nm thick Ir layer was formed on a (100) Si substrate by a sputtering method at a substrate temperature of 350 ° C.
Next, a 4.0 μm-thick Pb (Ti, Zr, Nb) O ₃ piezoelectric film was formed by sputtering at a substrate temperature of 525 ° C. As a target, Pb (Ti, Zr, Nb) O ₃ having a Zr / Ti molar ratio = 48/52 and an amount of Nb in the B site = 12 mol% was used.

  When the obtained piezoelectric film was subjected to X-ray diffraction (XRD) measurement, it was a perovskite single phase (100) preferential alignment film (orientation ratio = 95% or more). When the composition analysis was conducted by XRF, the composition of the obtained piezoelectric film was as follows: Zr / Ti molar ratio = 48/52, Nb amount in B site = 12 mol%.

  Next, a 0.2 μm-thick Pt upper electrode was formed to obtain the piezoelectric element of the present invention. When the bipolar polarization-electric field characteristics (PE hysteresis characteristics) were measured, there were coercive electric field points on the negative electric field side and the positive electric field side, respectively, and the absolute value of the coercive electric field Ec1 on the negative electric field side and the resistance on the positive electric field side. Asymmetric hysteresis different from the electric field Ec2 was shown. Ec1 = −10 kV / cm and Ec2 = 40 kV / cm (Ec2> | Ec1 |). (3 × Ec1 + 1 × Ec2) / (3 + 1) = 2.5, and the obtained piezoelectric film satisfied Ec1 ≦ 0 ≦ (3 × Ec1 + 1 × Ec2) / (3 + 1) (Characteristic (4- Satisfies A)).

Finally, an ink chamber was formed by dry etching the back side of the Si substrate, and an ink jet recording head was obtained by processing the substrate itself to form a diaphragm and an ink nozzle having an ink chamber and an ink discharge port. . The piezoelectric constant d _{31 at} driving conditions 0 to 200 kV / cm was 250 pm / V.

(Comparative Example 1)
A piezoelectric element and an ink jet recording head were obtained and evaluated in the same manner as in Example 1 except that the amount of Nb in the B site of the piezoelectric film was changed to 0 mol%.

(Evaluation results)
The evaluation results of Example 1 and Comparative Example 1 are shown in Table 1. In the table, the shift amount S = (Ec1 + Ec2) / 2.
By changing the Nb doping amount, the hysteresis property of the bipolar polarization-electric field characteristics could be adjusted. Moreover, in Example 1 that satisfies the characteristic (4-A), a larger piezoelectric constant was obtained than in Comparative Example 1 that did not satisfy the characteristic (4-A).

  The piezoelectric body of the present invention includes a piezoelectric actuator mounted on an ink jet recording head, a magnetic recording / reproducing head, a MEMS (Micro Electro-Mechanical Systems) device, a micro pump, an ultrasonic probe, etc., and a ferroelectric memory (FRAM). ) And the like.

In the case of Ec2> | Ec1 |, the polarization-electric field hysteresis curve (PE hysteresis curve), bipolar electric field-strain curve, and unipolar electric field-strain curve of the first to fourth piezoelectric bodies of the present invention are schematically shown. Illustration FIG. 1 is a diagram illustrating the unipolar electric field-strain curve (solid line) in FIG. 1 and the unipolar electric field-strain curve (broken line) of the piezoelectric body described in Patent Document 1 in FIG. In the case of Ec2 <| Ec1 |, the polarization-electric field hysteresis curve (PE hysteresis curve), bipolar electric field-strain curve, and unipolar electric field-strain curve of the first to fourth piezoelectric bodies of the present invention are schematically shown. Illustration The figure which shows typically the polarization-electric field curve, electric field-strain curve, and electric field-180 degree domain amount curve of the 2nd piezoelectric material of this invention. The figure which shows typically the polarization-electric field curve of the 3rd piezoelectric material of this invention, an electric field-strain curve, and an inversion current characteristic curve. The figure which shows typically the polarization-electric field curve and electric field-strain curve in case the polarization-electric field hysteresis characteristic is symmetrical in the 5th piezoelectric material of this invention. FIG. 10 is a diagram schematically showing a polarization-electric field curve and an electric field-strain curve when the polarization-electric field hysteresis characteristic is symmetric in the sixth piezoelectric body of the present invention. A diagram schematically showing the piezoelectric characteristics of a piezoelectric body consisting only of a ferroelectric phase that has the property of phase transition to another ferroelectric phase with a different crystal system when an electric field is applied. 1 is a cross-sectional view of an essential part showing the structure of a piezoelectric element according to an embodiment of the present invention and an ink jet recording head (liquid ejecting apparatus) including the same. The figure which shows the structural example of the inkjet recording device provided with the inkjet recording head of FIG. Partial top view of the ink jet recording apparatus of FIG. The figure which shows the polarization-electric field characteristic of the piezoelectric material film of a nonpatent literature 1 The figure which shows the voltage-strain characteristic of the piezoelectric material film of a nonpatent literature 1 The figure which shows typically the polarization-electric field curve and electric field-strain curve of the conventional general piezoelectric material which non-180 degree domain rotation occurs The figure which shows typically the polarization-electric field curve and electric field-strain curve of a piezoelectric material film of patent document 1 FIG. 14 is a diagram showing the unipolar electric field-strain curve (solid line) of the piezoelectric body described in Patent Document 1 in FIG. 14 together with the unipolar electric field-strain curve (broken line) in FIG.

Explanation of symbols

1 Piezoelectric element 3, 3K, 3C, 3M, 3Y Inkjet recording head (liquid ejection device)
12, 14 Electrode 13 Piezoelectric body 15 Control means 20 Ink nozzle (liquid storage and discharge member)
21 Ink chamber (liquid storage chamber)
22 Ink ejection port (liquid ejection port)
100 Inkjet recording device

Claims (22)

An asymmetric bipolar polarization made of a ferroelectric material, having a coercive electric field point on each of the negative electric field side and the positive electric field side, wherein the absolute value of the coercive electric field Ec1 on the negative electric field side and the coercive electric field Ec2 on the positive electric field side are different. In a piezoelectric body having electric field hysteresis characteristics,
A piezoelectric body having the following characteristic (1-A) or characteristic (1-B):
Characteristic (1-A): Ec2> | Ec1 |, and the bipolar electric field-strain curve has an inflection point in a curved portion from electric field Emax to Ec1 showing the maximum displacement on the positive electric field side. When the electric field at the bending point is Eif1, Ec1 ≦ 0 ≦ Eif1 is satisfied.
Characteristic (1-B): Ec2 <| Ec1 |, and the bipolar electric field-strain curve has an inflection point in the curved portion from electric field Emin to Ec2 showing the maximum displacement on the negative electric field side. When the electric field at the bending point is Eif2, Eif2 ≦ 0 ≦ Ec2 is satisfied. An asymmetric bipolar polarization made of a ferroelectric material, having a coercive electric field point on each of the negative electric field side and the positive electric field side, wherein the absolute value of the coercive electric field Ec1 on the negative electric field side and the coercive electric field Ec2 on the positive electric field side are different. In a piezoelectric body having electric field hysteresis characteristics,
A piezoelectric body having the following characteristic (2-A) or characteristic (2-B):
Characteristic (2-A): Ec2> | Ec1 |, and when the electric field at which the 180 ° domain inversion starts when the applied electric field is reduced from Ec2 is E180s1, Ec1 ≦ 0 ≦ E180s1 is satisfied.
Characteristic (2-B): Ec2 <| Ec1 |, and E180s2 ≦ 0 ≦ Ec2 is satisfied when E180s2 is an electric field at which 180 ° domain inversion starts when the applied electric field is increased from Ec1. An asymmetric bipolar polarization made of a ferroelectric material, having a coercive field point on each of the negative electric field side and the positive electric field side, wherein the absolute value of the coercive electric field Ec1 on the negative electric field side and the coercive electric field Ec2 on the positive electric field side are different. In a piezoelectric body having electric field hysteresis characteristics,
A piezoelectric body having the following characteristic (3-A) or characteristic (3-B):
Characteristic (3-A): Ec2> | Ec1 |, and when the electric field at which the reversal current value starts to increase when the applied electric field is decreased from Ec2 is Eics1 in the reversal current characteristic curve, Ec1 ≦ 0 ≦ Eics1 is satisfied.
Characteristic (3-B): When Ec2 <| Ec1 | and the electric field at which the reversal current value starts to increase when the applied electric field is increased from Ec1 in the reversal current characteristic curve is Eics2, Eics2 ≦ 0 ≦ Ec2 is satisfied. An asymmetric bipolar polarization made of a ferroelectric material, having a coercive electric field point on each of the negative electric field side and the positive electric field side, wherein the absolute value of the coercive electric field Ec1 on the negative electric field side and the coercive electric field Ec2 on the positive electric field side are different. In a piezoelectric body having electric field hysteresis characteristics,
A piezoelectric body having the following characteristic (4-A) or characteristic (4-B):
Characteristic (4-A): Ec2> | Ec1 |, and Ec1 ≦ 0 ≦ (3 × Ec1 + 1 × Ec2) / (3 + 1) is satisfied.
Characteristic (4-B): Ec2 <| Ec1 |, and (1 × Ec1 + 3 × Ec2) / (1 + 3) ≦ 0 ≦ Ec2 is satisfied. In a piezoelectric body made of a ferroelectric material and having a polarization field-hysteresis curve having a coercive field point on each of a negative electric field side and a positive electric field side,
When the coercive electric field on the negative electric field side and the coercive electric field on the positive electric field side in the bipolar polarization-electric field hysteresis curve are Ec1 and Ec2, respectively, the following characteristic (1-A) is obtained and the following driving condition (i-A) Or a piezoelectric body having the following characteristics (1-B) and driven under the following driving conditions (i-B).
Characteristic (1-A): When the bipolar electric field-strain curve has an inflection point in the curve portion from the electric field Emax to Ec1 showing the maximum displacement on the positive electric field side, and the electric field at the inflection point is Eif1. Ec1 ≦ 0 ≦ Eif1 is satisfied.
Driving condition (i-A): Ec1 ≦ Es ≦ Eif1 is satisfied, where Es is the minimum applied electric field for driving.
Characteristic (1-B): When the bipolar electric field-strain curve has an inflection point in a curved portion from electric field Emin to Ec2 showing the maximum displacement on the negative electric field side, and the electric field at the inflection point is Eif2. Eif2 ≦ 0 ≦ Ec2 is satisfied.
Driving condition (i-B): Eif2 ≦ Ee ≦ Ec2 is satisfied, where Ee is the maximum applied electric field for driving. In a piezoelectric body made of a ferroelectric material and having a polarization field-hysteresis curve having a coercive field point on each of a negative electric field side and a positive electric field side,
When the coercive electric field on the negative electric field side and the coercive electric field on the positive electric field side in the bipolar polarization-electric field hysteresis curve are Ec1 and Ec2, respectively, the following characteristic (2-A) is obtained and the following driving condition (ii-A) Or a piezoelectric body having the following characteristic (2-B) and driven under the following driving condition (ii-B).
Characteristic (2-A): Ec1 ≦ 0 ≦ E180s1 is satisfied when the electric field at which the 180 ° domain inversion starts when the applied electric field is decreased from Ec2 is E180s1.
Driving condition (ii-A): When the minimum applied electric field for driving is Es, Ec1 ≦ Es ≦ E180s1 is satisfied.
Characteristic (2-B): E180s2 ≦ 0 ≦ Ec2 is satisfied when the electric field at which the 180 ° domain inversion starts when the applied electric field is increased from Ec1 is E180s2.
Driving condition (ii-B): When the maximum applied electric field for driving is Ee, 180s2 ≦ Ee ≦ Ec2 is satisfied. In a piezoelectric body made of a ferroelectric material and having a polarization field-hysteresis curve having a coercive field point on each of a negative electric field side and a positive electric field side,
When the coercive electric field on the negative electric field side and the coercive electric field on the positive electric field side in the bipolar polarization-electric field hysteresis curve are Ec1 and Ec2, respectively, the following characteristic (3-A) is obtained and the following driving condition (iii-A) Or a piezoelectric body having the following characteristic (3-B) and driven under the following driving condition (iii-B).
Characteristic (3-A): In the reversal current characteristic curve, when the electric field at which the reversal current value starts to increase when the applied electric field is decreased from Ec2, Ec1 ≦ 0 ≦ Eics1 is satisfied.
Driving condition (iii-A): When the minimum applied electric field for driving is Es, Ec1 ≦ Es ≦ Eics1 is satisfied.
Characteristic (3-B): In the reversal current characteristic curve, when the electric field at which the reversal current value starts to increase when the applied electric field is increased from Ec1, Eics2 ≦ 0 ≦ Ec2 is satisfied.
Driving condition (iii-B): Eics2 ≦ Ee ≦ Ec2 is satisfied, where Ee is the maximum applied electric field for driving. In a piezoelectric body made of a ferroelectric material and having a polarization field-hysteresis curve having a coercive field point on each of a negative electric field side and a positive electric field side,
When the coercive electric field on the negative electric field side and the coercive electric field on the positive electric field side in the bipolar polarization-electric field hysteresis curve are Ec1 and Ec2, respectively, the following characteristic (4-A) is obtained and the following driving condition (iv-A) Or a piezoelectric body having the following characteristic (4-B) and driven under the following driving condition (iv-B).
Characteristic (4-A): Ec1 ≦ 0 ≦ (3 × Ec1 + 1 × Ec2) / (3 + 1) is satisfied.
Driving condition (iv-A): When the minimum applied electric field for driving is Es, Ec1 ≦ Es ≦ (3 × Ec1 + 1 × Ec2) / (3 + 1) is satisfied.
Characteristic (4-B): (1 × Ec1 + 3 × Ec2) / (1 + 3) ≦ 0 ≦ Ec2 is satisfied.
Driving condition (iv−B): When the maximum applied electric field for driving is Ee, (1 × Ec1 + 3 × Ec2) / (1 + 3) ≦ Ee ≦ Ec2 is satisfied.   The piezoelectric body according to claim 1, wherein the piezoelectric body is made of one or more perovskite oxides (may contain inevitable impurities). The piezoelectric body according to claim 9, comprising one or more perovskite oxides represented by the following general formula (P) (which may contain inevitable impurities).
General formula ABO ₃ (P)
(In the formula, A: an element at the A site, and at least one element selected from the group consisting of Pb, Ba, La, Sr, Bi, Li, Na, Ca, Cd, Mg, and K;
B: Element of B site, Ti, Zr, V, Nb, Ta, Cr, Mo, W, Mn, Sc, Co, Cu, In, Sn, Ga, Zn, Cd, Fe, Ni, and lanthanide element At least one element selected from the group consisting of:
O: oxygen element,
It is standard that the number of moles of the A-site element is 1.0, the number of moles of the B-site element is 1.0, and the number of moles of the oxygen element is 3.0, but these mole numbers are perovskite. It may deviate from the reference number of moles within a range where the structure can be taken. )   It is represented by the general formula (P), and the A site is composed of at least one metal element selected from the group consisting of Pb, Ba, Sr, Ca, and Mg, and the B site is composed of Zr and Ti. A perovskite oxide comprising at least one metal element selected from the group consisting of and at least one metal element selected from the group consisting of V, Nb, Ta, Cr, Mo, and W. The piezoelectric body according to claim 10.   The piezoelectric body according to claim 1, wherein the piezoelectric body is a piezoelectric film or a piezoelectric ceramic sintered body.   The piezoelectric body according to claim 1, comprising a ferroelectric phase having crystal orientation.   14. The piezoelectric body according to claim 13, comprising a ferroelectric phase having crystal orientation in a direction different from the spontaneous polarization axis direction. The ferroelectric phase having crystal orientation in a direction different from the direction of spontaneous polarization axis,
Rhombohedral phase having crystal orientation in the approximately <100> direction, rhombohedral phase having crystal orientation in the approximately <110> direction, tetragonal phase having crystal orientation in the approximately <110> direction, approximately <111 Selected from the group consisting of a tetragonal phase having crystal orientation in the> direction, an orthorhombic phase having crystal orientation in the <100> direction, and an orthorhombic phase having crystal orientation in the <111> direction. The piezoelectric body according to claim 14, wherein the piezoelectric body is at least one ferroelectric phase.   The ferroelectric phase having crystal orientation in a direction different from the spontaneous polarization axis direction is such that at least part of the ferroelectric phase is applied by applying an electric field in a direction different from the spontaneous polarization axis direction of the ferroelectric phase. 16. The piezoelectric body according to claim 14, wherein the piezoelectric body has a property of phase transition to another ferroelectric phase having a different crystal system. In the method of driving a piezoelectric body made of a ferroelectric material and having a bipolar polarization-electric field hysteresis curve having coercive electric field points on the negative electric field side and the positive electric field side,
When the coercive electric field on the negative electric field side and the coercive electric field on the positive electric field side are respectively Ec1 and Ec2 in the bipolar polarization-electric field hysteresis curve, a piezoelectric body having the following characteristic (1-A) is represented by the following driving condition (i-A). Or a piezoelectric body having the following characteristic (1-B) is driven under the following driving condition (i-B).
Characteristic (1-A): When the bipolar electric field-strain curve has an inflection point in the curve portion from the electric field Emax to Ec1 showing the maximum displacement on the positive electric field side, and the electric field at the inflection point is Eif1. Ec1 ≦ 0 ≦ Eif1 is satisfied.
Driving condition (i-A): Ec1 ≦ Es ≦ Eif1 is satisfied, where Es is the minimum applied electric field for driving.
Characteristic (1-B): When the bipolar electric field-strain curve has an inflection point in a curved portion from electric field Emin to Ec2 showing the maximum displacement on the negative electric field side, and the electric field at the inflection point is Eif2. Eif2 ≦ 0 ≦ Ec2 is satisfied.
Driving condition (i-B): Eif2 ≦ Ee ≦ Ec2 is satisfied, where Ee is the maximum applied electric field for driving. In the method of driving a piezoelectric body made of a ferroelectric material and having a bipolar polarization-electric field hysteresis curve having coercive electric field points on the negative electric field side and the positive electric field side,
When the coercive electric field on the negative electric field side and the coercive electric field on the positive electric field side are respectively Ec1 and Ec2 in the bipolar polarization-electric field hysteresis curve, a piezoelectric body having the following characteristic (2-A) is represented by the following driving condition (ii-A). Or a piezoelectric body having the following characteristic (2-B) is driven under the following driving condition (ii-B).
Characteristic (2-A): Ec1 ≦ 0 ≦ E180s1 is satisfied when the electric field at which the 180 ° domain inversion starts when the applied electric field is decreased from Ec2 is E180s1.
Driving condition (ii-A): When the minimum applied electric field for driving is Es, Ec1 ≦ Es ≦ E180s1 is satisfied.
Characteristic (2-B): E180s2 ≦ 0 ≦ Ec2 is satisfied when the electric field at which the 180 ° domain inversion starts when the applied electric field is increased from Ec1 is E180s2.
Driving condition (ii-B): When the maximum applied electric field for driving is Ee, 180s2 ≦ Ee ≦ Ec2 is satisfied. In the method of driving a piezoelectric body made of a ferroelectric material and having a bipolar polarization-electric field hysteresis curve having coercive electric field points on the negative electric field side and the positive electric field side,
When the coercive electric field on the negative electric field side and the coercive electric field on the positive electric field side in the bipolar polarization-electric field hysteresis curve are Ec1 and Ec2, respectively, a piezoelectric body having the following characteristic (3-A) is represented by the following drive condition (iii-A) Or a piezoelectric body having the following characteristic (3-B) is driven under the following driving condition (iii-B).
Characteristic (3-A): In the reversal current characteristic curve, when the electric field at which the reversal current value starts to increase when the applied electric field is decreased from Ec2, Ec1 ≦ 0 ≦ Eics1 is satisfied.
Driving condition (iii-A): When the minimum applied electric field for driving is Es, Ec1 ≦ Es ≦ Eics1 is satisfied.
Characteristic (3-B): In the reversal current characteristic curve, when the electric field at which the reversal current value starts to increase when the applied electric field is increased from Ec1, Eics2 ≦ 0 ≦ Ec2 is satisfied.
Driving condition (iii-B): Eics2 ≦ Ee ≦ Ec2 is satisfied, where Ee is the maximum applied electric field for driving. In the method of driving a piezoelectric body made of a ferroelectric material and having a bipolar polarization-electric field hysteresis curve having coercive electric field points on the negative electric field side and the positive electric field side,
When the coercive electric field on the negative electric field side and the coercive electric field on the positive electric field side in the bipolar polarization-electric field hysteresis curve are Ec1 and Ec2, respectively, a piezoelectric body having the following characteristic (4-A) is represented by the following driving condition (iv-A). Or a piezoelectric body having the following characteristic (4-B) is driven under the following driving condition (iv-B).
Characteristic (4-A): Ec1 ≦ 0 ≦ (3 × Ec1 + 1 × Ec2) / (3 + 1) is satisfied.
Driving condition (iv-A): When the minimum applied electric field for driving is Es, Ec1 ≦ Es ≦ (3 × Ec1 + 1 × Ec2) / (3 + 1) is satisfied.
Characteristic (4-B): (1 × Ec1 + 3 × Ec2) / (1 + 3) ≦ 0 ≦ Ec2 is satisfied.
Driving condition (iv−B): When the maximum applied electric field for driving is Ee, (1 × Ec1 + 3 × Ec2) / (1 + 3) ≦ Ee ≦ Ec2 is satisfied.   A piezoelectric element comprising the piezoelectric body according to claim 1 and an electrode for applying an electric field to the piezoelectric body. A piezoelectric element according to claim 21;
A liquid discharge apparatus comprising: a liquid storage chamber in which liquid is stored; and a liquid storage / discharge member having a liquid discharge port through which the liquid is discharged from the liquid storage chamber.

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