JP7491838B2 - Dielectric composition, dielectric element and electronic component - Google Patents

Description

The present invention relates to a dielectric composition, a dielectric element comprising the dielectric composition, and an electronic component comprising a dielectric layer and an electrode made of the dielectric composition.

Multilayer ceramic capacitors, one example of electronic components, are used in many electronic devices due to their high reliability and low cost.

Specific examples of electronic devices include information terminals such as mobile phones, home appliances, and automotive electrical equipment. Among these, multilayer ceramic capacitors used in vehicles are required to be able to operate at higher temperatures than multilayer ceramic capacitors used in home appliances and information terminals.

Patent Document 1 discloses a dielectric ceramic containing a perovskite compound represented by (Ba1 _-x-y , _Cax , _Sry ) (Ti1 _-a , _Gea ) _O3 as a main component and containing a Si compound in an amount of 0 < Si ≦ 0.20 mol parts in terms of Si per 1 mol part of the main component. Patent Document 1 also describes that the dielectric ceramic has a good high temperature load life determined from the change over time in insulation resistance when 60 V is applied at 125°C.

Patent Document 2 discloses a dielectric composition containing a main component represented by the chemical formula (A6 _{- xBxCx +2D8 - xO30} , 0≦x≦5), where A is Ba or the like, B is Y or the like, C is Ti or the like, and D is Nb or the like, and an oxide of Ge as a first minor component in an amount of 2.50 mol to 20.0 mol per 100 mol of the main component. Patent Document 2 also discloses that the high-temperature loaded life calculated from the change over time in the resistivity at 225°C and the insulation resistance when 40 V/μm is applied at 250°C is good.

JP 2012-25592 A JP 2018-135258 A

However, the high-temperature load life of the dielectric ceramic described in Patent Document 1 is evaluated at 125°C, and the resistivity in high temperature ranges, for example, above 150°C, is not evaluated. Furthermore, the dielectric constant of the dielectric ceramic described in Patent Document 1 is not evaluated.

In addition, the dielectric composition described in Patent Document 2 had an insufficient relative dielectric constant.

The present invention has been made in consideration of these circumstances, and aims to provide a dielectric composition that has a high relative dielectric constant and exhibits high resistivity in a high temperature range, and an electronic component that includes a dielectric layer and electrodes made of the dielectric composition.

In order to achieve the above object, the present invention is characterized in that:
[1] A dielectric composition containing, as a main component, a complex oxide having a tungsten bronze type crystal structure and represented by the chemical formula _{A6-xBx ( GeyC1 -y} ) _{x+ 2D8- xO30+σ} ,
A is at least one element selected from the group consisting of Ba, Ca and Sr;
B is at least one element selected from the group consisting of Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu;
C is at least one element selected from the group consisting of Zr and Ti;
D is at least one element selected from the group consisting of Nb and Ta;
The dielectric composition is one in which x and y satisfy the relationships 0≦x≦3 and 0.001≦y≦0.04.

[2] The dielectric composition has dielectric particles containing a composite oxide and grain boundaries present between the dielectric particles,
The dielectric composition according to [1], wherein when an average concentration of Ge in the dielectric particles is C1 mass % and an average concentration of Ge in the grain boundaries is C2 mass %, C1 and C2 satisfy the relationship C1/C2>10.

[3] A dielectric element comprising the dielectric composition described in [1] or [2].

[4] An electronic component comprising a dielectric layer containing the dielectric composition described in [1] or [2] and an electrode.

The present invention provides a dielectric composition that has a high dielectric constant and exhibits high resistivity at high temperatures, and an electronic component that includes a dielectric layer and electrodes made of the dielectric composition.

FIG. 1 is a cross-sectional view of a multilayer ceramic capacitor according to one embodiment of the present invention. FIG. 2 is a diagram showing the results of point analysis of Ge on the line segment shown in FIG. 2 in an embodiment of the present invention.

The present invention will now be described in detail based on specific embodiments in the following order.
1. Multilayer ceramic capacitor 1.1. Overall configuration of multilayer ceramic capacitor 1.2. Dielectric layer 1.3. Internal electrode layer 1.4. External electrode 2. Dielectric composition 2.1. Complex oxide 3. Manufacturing method of multilayer ceramic capacitor 4. Summary of this embodiment 5. Modifications

(1. Multilayer ceramic capacitors)
(1.1. Overall configuration of multilayer ceramic capacitor)
A multilayer ceramic capacitor 1 as an example of an electronic component according to this embodiment is shown in Fig. 1. The multilayer ceramic capacitor 1 has an element body 10 in which dielectric layers 2 and internal electrode layers 3 are alternately laminated. A pair of external electrodes 4 are formed on both ends of the element body 10, and are electrically connected to the internal electrode layers 3 arranged alternately inside the element body 10. There is no particular restriction on the shape of the element body 10, but it is usually a rectangular parallelepiped. There is also no particular restriction on the dimensions of the element body 10, and the dimensions may be appropriate depending on the application.

(1.2. Dielectric Layer)
The dielectric layers 2 are made of a dielectric composition according to the present embodiment, which will be described later. As a result, a multilayer ceramic capacitor having the dielectric layers 2 has a high relative dielectric constant and can exhibit high resistivity even in a high temperature range.

The thickness of each layer of the dielectric layer 2 (interlayer thickness) is not particularly limited, and can be set arbitrarily according to the desired characteristics, applications, etc. Usually, the interlayer thickness is preferably 100 μm or less, and more preferably 30 μm or less. In this embodiment, the lower limit of the interlayer thickness is not particularly limited, but is, for example, about 0.5 μm. In addition, the number of layers of the dielectric layer 2 is not particularly limited, but in this embodiment, it is preferably, for example, 20 or more, and more preferably 50 or more.

(1.3. Internal electrode layer)
In this embodiment, the internal electrode layers 3 are laminated so that their end faces are alternately exposed on the surfaces of two opposing ends of the element body 10 .

The conductive material contained in the internal electrode layer 3 is not particularly limited. In this embodiment, Ni, a Ni-based alloy, Cu or a Cu-based alloy is preferable. More preferably, it is Ni or a Ni-based alloy. Even more preferably, the main component of the internal electrode layer 3 is Ni or a Ni-based alloy, and the conductive material contains one or more types selected from Al, Si, Li, Cr and Fe as a secondary component. The main component of the internal electrode layer 3 refers to a component contained in an amount of 85 mass% or more of the entire internal electrode layer 3.

The internal electrode layer 3 contains Ni or a Ni-based alloy as a main component and one or more selected from Al, Si, Li, Cr, and Fe as a secondary component, so that the Ni contained in the internal electrode layer 3 is less likely to oxidize. Even if the multilayer ceramic capacitor 1 is continuously used at a high temperature of about 250°C, the continuity and conductivity of the internal electrode layer 3 are less likely to deteriorate due to oxidation of the internal electrode layer 3.

The reason why the Ni contained in the internal electrode layer 3 is less likely to be oxidized when the internal electrode layer 3 contains one or more types selected from Al, Si, Li, Cr, and Fe as minor components is as follows. When the internal electrode layer 3 contains one or more types selected from Al, Si, Li, Cr, and Fe, the minor components react with oxygen before the Ni reacts with oxygen in the air to become NiO, forming an oxide film of the minor components on the surface of the Ni contained in the internal electrode 3. As a result, oxygen in the air cannot react with Ni without passing through the oxide film, making the Ni less likely to be oxidized.

The internal electrode layer 3 may contain various trace components such as P at about 0.1 mass % or less. The internal electrode layer 3 may be formed using a commercially available electrode paste. The thickness of the internal electrode layer 3 may be appropriately determined depending on the application, etc.

(1.4. External electrodes)
There is no particular limitation on the conductive material contained in the external electrodes 4. For example, known conductive materials such as Ni, Cu, Ag, Pd, Pt, Au, alloys of these, conductive resins, etc. may be used. The thickness of the external electrodes 4 may be appropriately determined depending on the application, etc.

2. Dielectric Composition
The dielectric composition according to the present embodiment contains a complex oxide having a tungsten bronze type crystal structure as a main component. Specifically, the complex oxide is contained in an amount of more than 50 mol %, and preferably 75 mol % or more, per 100 mol % of the dielectric composition according to the present embodiment.

(2.1. Composite oxides)
The composite oxide is represented by the chemical formula A6 _{-xBx ( GeyC1-y} ) _{x+ 2D8-} xO30 _+σ . In the chemical formula, the "A" element, the "B" element, Ge ( _germanium ), the "C" element, and the "D" element are divided based on the ionic valence. Specifically, the "A" element is a divalent element, the "B" element is a trivalent element, Ge and the "C" elements are tetravalent elements, and the "D" element is a pentavalent element.

In this embodiment, the "A" element is at least one element selected from the group consisting of Ba (barium), Ca (calcium), and Sr (strontium). The "A" element preferably contains at least Ba, and is more preferably Ba.

The "B" element is at least one element selected from the group consisting of Y (yttrium), La (lanthanum), Pr (praseodymium), Nd (neodymium), Sm (samarium), Eu (europium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Ho (holmium), Er (erbium), Tm (thulium), Yb (ytterbium) and Lu (lutetium). The "B" element preferably includes at least La, and is more preferably La.

The "C" element is at least one element selected from the group consisting of Zr (zirconium) and Ti (titanium). The "C" element preferably includes at least Zr, and more preferably includes Zr and Ti.

The "D" element is at least one element selected from the group consisting of Nb (niobium) and Ta (tantalum). From the viewpoint of dielectric constant, it is preferable to include Nb, and from the viewpoint of resistivity, it is preferable to include Ta.

In the chemical formula, "x" indicates the composition ratio of the number of atoms of the "B" element. In this embodiment, "x" satisfies the relationship 0≦x≦3. In other words, the above complex oxide does not need to contain the "B" element. When "x" is within the above range, the crystal structure of the complex oxide tends to be a tungsten bronze type crystal structure.

The composition ratio of the "A" element (6-x), the total composition ratio of Ge and the "C" element (x+2), and the composition ratio of the "D" element (8-x) usually correspond to the value of "x". However, as long as the composite oxide has a tungsten bronze type crystal structure, these composition ratios do not necessarily correspond uniquely to the value of "x". That is, with respect to the composition ratio (x) of the number of atoms of the "B" element, the composition ratio of the "A" element can be expressed as "6-x+α", the total composition ratio of Ge and the "C" element can be expressed as "x+2+β", and the composition ratio of the "D" element can be expressed as "8-x+γ". In this embodiment, "α", "β", and "γ" independently satisfy the relationships of -0.10<α<0.10, -0.10<β<0.10, and -0.10<γ<0.10.

In the chemical formula, "y" indicates the composition ratio of Ge when the total number of atoms of tetravalent elements is 1. In this embodiment, "y" satisfies the relationship 0.001≦y≦0.04. "y" is preferably 0.005 or more, and more preferably 0.015 or more. On the other hand, "y" is preferably 0.03 or less, and more preferably 0.025 or less. When "y" is within the above range, the dielectric constant and resistivity at high temperatures (for example, 175°C) of the dielectric composition tend to be good.

In the tungsten bronze crystal structure, oxygen octahedra formed by six-coordination of oxygen to elements occupying the B site form a three-dimensional network that shares their vertices. Furthermore, elements occupying the A site are located in the gaps between the oxygen octahedra. The A site is divided into A1 site and A2 site depending on the difference in coordination number. The B site is also divided into B1 site and B2 site depending on the relative positions of the oxygen octahedra.

The sites occupied by the "A" element, "B" element, Ge, "C" element, and "D" element constituting the above composite oxide are not particularly limited, so long as the composite oxide has a tungsten bronze type crystal structure. However, taking into consideration the valence and ionic radius, etc., the "A" element and the "B" element usually tend to occupy the A site, and Ge, the "C" element, and the "D" element tend to occupy the B site. In particular, the "A" element tends to occupy the A1 site, the "B" element tends to occupy the A2 site, Ge and the "C" element tend to occupy the B1 site, and the "D" element tends to occupy the B2 site.

When the composition ratio (y) of Ge is within the above range, i.e., when the ratio of Ge substituting for the "C" element is within the above range, it is believed that the distortion of the oxygen octahedron of the "C" element becomes large, and the spontaneous polarization becomes large. As a result, the relative dielectric constant of the dielectric composition tends to improve.

In particular, when Zr and Ti are included as "C" elements, Ge tends to easily substitute for Zr. Since Ge has a smaller ionic radius than Zr, when Ge substitutes for Zr, the volume occupied by the oxygen octahedrons of Ti increases, and spontaneous polarization tends to become larger. Therefore, the relative dielectric constant of the dielectric composition tends to be further improved.

In addition, when Ge is contained in the dielectric composition, the migration of oxygen defects in the dielectric composition tends to be suppressed. As a result, the resistivity of the dielectric composition at high temperatures is improved.

The dielectric composition according to this embodiment is a polycrystalline body, and has a large number of dielectric particles composed of the above-mentioned composite oxide, and grain boundaries that exist between the dielectric particles. In other words, the dielectric particles having a tungsten bronze type crystal structure are bonded via grain boundaries.

As described above, by substituting Ge for the "C" element, a dielectric composition with good relative permittivity and resistivity can be obtained. Therefore, in this embodiment, it is preferable that Ge is present in the dielectric particles having a tungsten bronze type crystal structure rather than in the grain boundaries. Specifically, when the average concentration of Ge in the dielectric particles is C1 mass % and the average concentration of Ge in the grain boundaries is C2 mass %, it is preferable that C1 and C2 satisfy the relationship C1/C2>10.

If this relationship is satisfied, the amount of Ge in the dielectric particles will be greater than the amount of Ge in the grain boundaries, increasing the probability that Ge will be present in the B1 site of the tungsten bronze crystal structure. As a result, the above-mentioned effects are more likely to be obtained. It is more preferable that C1/C2 is 20 or more, and even more preferable that it is 35 or more.

In the present embodiment, the following method is exemplified as a method for measuring C1 in the dielectric particles and C2 in the grain boundaries in a dielectric composition.

First, a scanning transmission electron microscope (STEM) is used to identify the dielectric particles and the grain boundaries between the dielectric particles in any cross section of the dielectric composition. The observation magnification may be determined according to the state of the dielectric composition sample so that the dielectric particles and the grain boundaries can be clearly identified. In addition, an example of a method for identifying the dielectric particles and the grain boundaries is a method for identifying them using the difference in contrast between the dielectric particles and the grain boundaries.

Next, in a region including dielectric particles and grain boundaries, a line segment is set that passes through two dielectric particles and the grain boundary that exists between them. The length of the line segment is not particularly limited as long as it is a length that allows the Ge concentration in the dielectric particles and the Ge concentration in the grain boundaries to be clearly distinguished and measured. Point analysis is performed on the line segment at sufficiently close intervals using an energy dispersive X-ray spectrometer (EDS) attached to the STEM. In this embodiment, it is preferable to perform point analysis at several tens of points at intervals of 1 to 2 nm on the set line segment, for example.

From the obtained point analysis results, the average value of the Ge concentration on the line segments corresponding to the dielectric particles is calculated, and the average value of the Ge concentration on the line segments corresponding to the grain boundaries is calculated. This point analysis is performed 3 to 15 times, and the average values are taken as the average Ge concentration in the dielectric particles (C1) and the average Ge concentration in the grain boundaries (C2). C1/C2 is calculated from the obtained C1 and C2.

(3. Manufacturing Method of Multilayer Ceramic Capacitor)
Next, an example of a method for manufacturing the multilayer ceramic capacitor 1 shown in FIG. 1 will be described below.

The multilayer ceramic capacitor 1 according to this embodiment can be manufactured by a known method similar to that used for conventional multilayer ceramic capacitors. One known method is, for example, a method in which a green chip is made using a paste containing the raw materials of a dielectric composition, and then the green chip is fired to manufacture a multilayer ceramic capacitor. The manufacturing method is described in detail below.

First, the starting material for the dielectric composition is prepared. In this embodiment, the starting material is preferably a powder. As the starting material for the dielectric composition, a calcined powder of the main component is prepared.

As the starting material for the calcined powder of the main component, the oxides of the metals contained in the above-mentioned composite oxide, which is the main component, or various compounds that become components of the composite oxide upon firing can be used. Examples of various compounds include carbonates, oxalates, nitrates, hydroxides, and organometallic compounds.

For example, prepare a carbonate powder of element "A", a hydroxide or oxide powder of element "B", an oxide powder of Ge and element "C", and an oxide powder of element "D". The average particle size of each powder can be adjusted so that the particle size of the dielectric particles that make up the composite oxide after firing is, for example, about 200 to 300 nm.

In this embodiment, the oxide powder of Ge is preferably a composite oxide powder of Ge and at least one element selected from the group consisting of the "A" element, the "B" element, the "C" element, and the "D" element. This is because _GeO2 , a typical single oxide of Ge, has a melting point lower than the firing temperature of the green chip, and _GeO2 becomes liquid during firing of the green chip and is likely to precipitate at the grain boundary. In other words, Ge is less likely to form a solid solution in the dielectric particles.

Examples of composite oxides of Ge and _an " _A " element include _{BaGeO4 , La2Ge3O9 , La2Ge2O7 , and 9Nb2O5.GeO2} .

Next, the prepared starting materials are weighed to have the above-mentioned composition, and then wet-mixed for a predetermined time using a ball mill or the like. After drying the mixed powder, heat treatment is performed in the air to obtain a calcined powder of the composite oxide, which is the main component. In this embodiment, the heat treatment temperature is preferably in the range of 1050 to 1200 ° C. By performing heat treatment in such a temperature range, even if the Ge oxide powder is GeO ₂ , it is easy to react with other main component elements in the heat treatment. Therefore, as a precursor of the composite oxide after heat treatment, a precursor in which Ge reacts with other main component elements is easily obtained. Even if a green chip containing such a precursor is fired, Ge is unlikely to precipitate at grain boundaries and is easily dissolved in dielectric particles. In addition, when the Ge oxide powder is a composite oxide of the above-mentioned Ge and the "A" element, etc., heat treatment in the above temperature range is preferable because Ge is easily dissolved in the dielectric particles.

The calcined powder of the main component is then crushed to obtain the raw powder of the dielectric composition. The average particle size of the raw powder of the dielectric composition is, for example, 0.5 μm to 2.0 μm.

Next, a paste for producing the green chip is prepared. The obtained dielectric composition raw material powder is kneaded with a binder and a solvent to form a paint, and a paste for the dielectric layer is prepared. The binder and the solvent may be publicly known. The paste for the dielectric layer may also contain additives such as a plasticizer, if necessary.

The internal electrode layer paste is obtained by kneading the above-mentioned conductive material raw material, a binder, and a solvent. The binder and the solvent may be publicly known. The internal electrode layer paste may contain additives such as co-materials and plasticizers as necessary.

The paste for the external electrodes can be prepared in the same manner as the paste for the internal electrode layers.

The binder and solvent contents in each of the above pastes are not particularly limited and may be normal contents. For example, the binder may be about 1% to 5% by mass, and the solvent may be about 10% to 50% by mass. In addition, each paste may contain additives selected from various dispersants, plasticizers, dielectric materials, insulating materials, etc., as necessary. The total content of these is preferably 10% by mass or less.

The dispersant may be, for example, a surfactant-type dispersant or a polymer-type dispersant. The plasticizer may be, for example, dioctyl phthalate or dibutyl phthalate. The dielectric material may be, for example, _BaTiO3 or _CaZrO3 . The insulating material may be, for example _{, Al2O3} or _SiO2 .

The resulting pastes are used to form green sheets and internal electrode patterns, which are then stacked to obtain green chips.

Before firing, the green chip is subjected to a binder removal process. The binder removal conditions are a temperature rise rate of preferably 5°C/hour to 300°C/hour, a holding temperature of preferably 180°C to 500°C, and a temperature holding time of preferably 0.5 hours to 24 hours. The atmosphere is air or a reducing atmosphere. In the binder removal process described above, the atmosphere may be humidified. Any method for humidification may be used. For example, a wetter or the like may be used. In this case, the water temperature is preferably about 5°C to 75°C.

After the binder removal process, the green chip is fired to obtain the element body. Examples of firing conditions include the following. The firing temperature is preferably 1100°C to 1400°C. If the firing temperature is too low, the element body will not be sufficiently densified. If the firing temperature is too high, abnormal sintering of the internal electrode layer will cause the electrodes to break, and the material that makes up the internal electrode layer will diffuse, making it more likely that the rate of capacitance change will deteriorate. Furthermore, particles made up of the main component will become coarse, which may shorten the high-temperature load life.

The heating rate is preferably 200°C/hour to 5000°C/hour. The temperature holding time during firing and the cooling rate after firing are optional. In order to control the particle size distribution of the dielectric particles composed of the main component after firing to within the range of 0.5 μm to 5.0 μm and to suppress volume diffusion between the dielectric particles, the temperature holding time is preferably 0.1 hour to 1.0 hour, and the cooling rate is preferably 100°C/hour to 500°C/hour.

In addition, the firing atmosphere is preferably a mixture of humidified _N2 and _H2 gas, with an oxygen partial pressure of ^10-2 to ^10-6 Pa. When the internal electrode layer contains Ni, firing under high oxygen partial pressure conditions may result in Ni being oxidized and the electrical conductivity may be reduced. However, by adding one or more types of internal electrode subcomponents selected from Al, Si, Li, Cr, and Fe to a conductive material mainly composed of Ni, the oxidation resistance of Ni is improved, and it is easy to ensure the electrical conductivity of the internal electrode layer even when firing in an atmosphere with a high oxygen partial pressure.

After firing, the obtained element body is annealed as necessary. The annealing conditions may be known conditions, and for example, it is preferable that the oxygen partial pressure during the annealing is higher than the oxygen partial pressure during firing, and that the holding temperature is 1000°C or less.

The above-mentioned binder removal process, firing and annealing processes may be carried out independently or consecutively.

The dielectric composition constituting the dielectric layer of the element body obtained as described above is the dielectric composition described above. The end faces of this element body are polished, and an external electrode paste is applied and baked to form the external electrode 4. Then, if necessary, a coating layer is formed on the surface of the external electrode 4 by plating or the like.

In this manner, the multilayer ceramic capacitor according to this embodiment is manufactured.

(4. Summary of the present embodiment)
In this embodiment, in a dielectric composition having a complex oxide having a tungsten bronze type crystal structure as a main component, Ge is contained in the complex oxide within the above-mentioned range. By doing so, the movement of oxygen defects is inhibited in the dielectric particles. That is, the movement of electrons that occurs together with the oxygen defects is also inhibited. Therefore, the resistivity of the dielectric composition in the high temperature range is improved.

In addition, when Ge is dissolved in the B1 site of the complex oxide in the dielectric composition, the volume of the oxygen octahedron of the "C" element increases, resulting in increased spontaneous polarization and an improved dielectric constant.

Furthermore, when the average Ge concentration C1 in the dielectric composition and the average Ge concentration C2 in the grain boundaries satisfy the above-mentioned relationship, the probability that Ge will dissolve in the B1 site increases, further improving the relative dielectric constant.

(5. Modifications)
In the above embodiment, the electronic component according to the present embodiment is a multilayer ceramic capacitor, but the electronic component according to the present embodiment is not limited to a multilayer ceramic capacitor and may be any electronic component that includes a dielectric layer having the above-mentioned dielectric composition and an electrode. It may also be a dielectric element that includes the above-mentioned dielectric composition.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments and may be modified in various ways within the scope of the present invention.

The present invention will be described in more detail below using examples and comparative examples. However, the present invention is not limited to the following examples.

(Experiment 1)
First, the following powders with an average particle size of 1.0 μm or less were prepared as starting materials for the main components. Carbonate powder was used as the raw material for the "A" element, hydroxide or oxide powder was used as the raw material for the "B" element, and oxide powder was used as the raw materials for Ge, "C" element, and "D" element.

For samples No. 1 to 51, _GeO2 was used as the Ge oxide powder. For samples No. 52, _{53, and 55, BaGeO4 was used as the Ge oxide powder. For sample No. 54, La2Ge3O9 was used as the Ge oxide powder. For samples No. 56 and 57, 9NbO5.GeO2 was used as the} Ge oxide powder.

These raw materials were weighed and mixed so that the composition ratio of each element in the composite oxide contained in the final dielectric composition was the ratio shown in Tables 1 and 2, and wet-mixed in a ball mill for 24 hours using ethanol as a dispersion medium. The resulting mixture was then dried to obtain a mixed raw material powder. For samples No. 50 and 51, raw materials other than the Ge oxide powder (GeO ₂ ) were mixed to obtain a mixed raw material powder.

Then, heat treatment was performed in air at a holding temperature of 1200°C for 2 hours to obtain the calcined powder of the main component.

The calcined powder of the main component obtained by the above method was crushed to obtain a dielectric composition raw material powder. Note that, for samples No. 50 and 51, after crushing the calcined powder of the main component obtained, a weighed amount of Ge oxide powder (GeO ₂ ) was mixed to obtain a dielectric composition raw material powder.

Next, 700 g of a solvent made by mixing a toluene + ethanol solution (toluene:ethanol = 50:50 (weight ratio)), a plasticizer (dioctyl phthalate (DOP) (manufactured by J-Plus)) and a dispersant (Marialim AKM-0531 (manufactured by NOF Corp.)) in a ratio of 90:6:4 (weight ratio) was added to 1000 g of the dielectric composition raw material powder to obtain a mixture. Next, the obtained mixture was dispersed for 2 hours using a basket mill to prepare a dielectric layer paste. Note that the viscosity of the dielectric layer paste was adjusted to approximately 200 cps for all samples. Specifically, the viscosity was adjusted by adding a small amount of a toluene + ethanol solution.

As raw materials for the internal electrode layer, Ni powder with an average particle size of 0.2 μm, Al oxide powder with an average particle size of 0.1 μm or less, and Si oxide powder with an average particle size of 0.1 μm or less were prepared. These powders were weighed and mixed so that the total of Al and Si was 5 mass% relative to Ni. Then, the powder was heat-treated at 1200 ° C or more in a mixed gas of humidified N ₂ and H _2. The powder after the heat treatment was crushed by a ball mill or the like to prepare raw material powder for the internal electrode layer with an average particle size of 0.20 μm.

100% by mass of the raw material powder for the internal electrode layer, 30% by mass of an organic vehicle (8% by mass of ethyl cellulose resin dissolved in 92% by mass of butyl carbitol), and 8% by mass of butyl carbitol were kneaded and made into a paste using a three-roll mill to obtain a paste for the internal electrode layer.

The prepared dielectric layer paste was then applied onto a PET film to form a green sheet. At this time, the thickness of the green sheet after drying was set to 10 μm. Next, a predetermined pattern of internal electrode layers was printed onto the green sheet using the internal electrode layer paste. The green sheet was then peeled off from the PET film to produce a green sheet on which the internal electrode layers were printed in the predetermined pattern. Next, multiple green sheets on which the internal electrode layers were printed in the predetermined pattern were stacked and pressure-bonded to form a green laminate. Furthermore, the green laminate was cut into a predetermined shape to obtain a green chip.

Then, the obtained green chip was subjected to a binder removal process, firing and annealing process to obtain a multilayer ceramic fired body (element body). The conditions for the binder removal process, firing and annealing are as shown below. In addition, a wetter was used to humidify the atmospheric gas during the binder removal process, firing and annealing processes.

(Debinding process)
Heating rate: 100°C/hour Holding temperature: 400°C
Temperature retention time: 8.0 hours Atmospheric gas: mixed gas of humidified _N2 and _H2

(Firing)
Heating rate: 500°C/hour Firing temperature: 1200°C to 1350°C
Temperature retention time: 0.5 hours Cooling rate: 100°C/hour Atmosphere gas: mixed gas of humidified _N2 and _H2 Oxygen partial pressure: ^10-5 to ^10-9 Pa

(Annealing treatment)
Holding temperature: 800°C to 1000°C
Temperature retention time: 2.0 hours Temperature increase and decrease rate: 200°C/hour Atmospheric gas: humidified _N2 gas

The dielectric layers (dielectric compositions) of each of the obtained fired laminated ceramic bodies were subjected to composition analysis using ICP emission spectroscopy, and it was confirmed that the compositions after analysis were the same as those shown in Tables 1 and 2. In addition, X-ray diffraction measurements were performed on the dielectric compositions, and it was confirmed from the obtained X-ray diffraction pattern that the dielectric composition of sample No. 21 did not have a tungsten bronze type crystal structure, and the dielectric compositions other than sample No. 21 had a tungsten bronze type crystal structure.

The end faces of the obtained fired laminated ceramic body were polished by sandblasting, and then an In-Ga eutectic alloy was applied as an external electrode to obtain each laminated ceramic capacitor sample having the same shape as the laminated ceramic capacitor shown in Figure 1. The size of each of the obtained laminated ceramic capacitor samples was 3.2 mm x 1.6 mm x 1.2 mm, with a dielectric layer thickness of 7 μm, an internal electrode layer thickness of 2 μm, and 50 dielectric layers sandwiched between the internal electrode layers.

A cross section of the dielectric layer (dielectric composition) along the lamination direction of each of the obtained multilayer ceramic capacitor samples was polished, and the polished cross section was observed at a magnification of 100,000 times using a scanning transmission electron microscope (STEM) to identify the dielectric particles composed of the main component composite oxide and the grain boundaries.

Next, a straight line 50 to 100 nm long was set that included the two dielectric particles and the grain boundary between them, and point analysis was performed at 1 to 2 nm intervals along the straight line using an energy dispersive X-ray spectrometer (EDS) attached to the STEM to measure the Ge concentration.

This measurement was performed 10 times, and the average Ge concentration in the dielectric particles was taken as C1, and the average Ge concentration in the grain boundaries was taken as C2. C1/C2 was calculated from the obtained C1 and C2. The results are shown in Tables 1 and 2.

Figure 2 shows the results of the point analysis performed on sample No. 38. Figure 2 shows a graph of the change in Ge concentration on a straight line L with a length of 50 nm that includes two dielectric particles 21, 22 and the grain boundary 25 that exists between them.

The dielectric constant and resistivity of the obtained multilayer ceramic capacitor samples were measured using the methods described below.

(Dielectric constant)
A signal with a frequency of 1 kHz and an input signal level (measurement voltage) of 1 Vrms was input to the multilayer ceramic capacitor sample at 25° C. using a digital LCR meter (4284A manufactured by YHP Corporation) to measure the capacitance. The dielectric constant (unitless) was calculated based on the thickness of the dielectric layer, the effective electrode area, and the capacitance obtained as a result of the measurement. A higher dielectric constant is preferable. In this example, samples with a dielectric constant of 400 or more were judged to be good, and samples with a dielectric constant of 500 or more were judged to be more preferable. The results are shown in Tables 1 and 2.

(resistivity)
The insulation resistance of the multilayer ceramic capacitor samples was measured at 175° C. using a digital resistance meter (R8340 manufactured by ADVANTEST) at a measurement voltage of 200 V and a measurement time of 60 seconds. The specific resistance was calculated from the measured insulation resistance value, the electrode area of the multilayer ceramic capacitor sample, and the thickness of the dielectric layer. A higher specific resistance is preferable. In this example, samples with a specific resistance of 5.0×10 ¹² Ωcm or more were judged to be good. The results are shown in Tables 1 and 2.

Figure 2 confirms that the Ge concentration is high in the dielectric particles and very low at the grain boundaries. In other words, it was confirmed that Ge is hardly present at the grain boundaries, but is present in the dielectric particles.

Furthermore, from Tables 1 and 2, it was confirmed that when the composite oxide has a tungsten bronze type crystal structure and the composition ratio of Ge is within the above-mentioned range, a multilayer ceramic capacitor having a high relative dielectric constant and a high specific resistance at 175°C can be obtained.

In contrast, it was confirmed that at least one of the dielectric constant and resistivity was low when the composite oxide did not have a tungsten bronze crystal structure, when the Ge composition ratio was outside the above-mentioned range, and when the total composition ratio of Ge and the "C" element was outside the above-mentioned range.

It was also confirmed that, among the Ge contained in the dielectric composition, the amount of Ge present within the dielectric particles is greater than the amount of Ge present at the grain boundaries, and C1/C2 is within the above-mentioned range, the relative dielectric constant is further improved. It was also confirmed that, when a composite oxide is used as the Ge oxide, the relative dielectric constant and resistivity are improved.

The dielectric composition according to this embodiment can exhibit a high relative dielectric constant and a high resistivity at high temperatures. Therefore, it can be suitably used for electronic components for automotive applications that require use at high temperatures of about 175°C.

Reference Signs List 1... Multilayer ceramic capacitor 10... Element body 2... Dielectric layer 3... Internal electrode layer 4... External electrode

Claims (4)

A dielectric composition containing, as a main component, a complex oxide having a tungsten bronze type crystal structure and represented by a chemical formula _{A6-xBx ( GeyC1 -y} ) _{x+ 2D8-} xO30 _+σ ,
A is at least one element selected from the group consisting of Ba, Ca and Sr;
B is at least one element selected from the group consisting of Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu;
C is at least one element selected from the group consisting of Zr and Ti;
D is at least one element selected from the group consisting of Nb and Ta;
A dielectric composition, wherein x and y satisfy the relationships: 0≦x≦3, 0.001≦y≦0.04. The dielectric composition has dielectric particles containing the composite oxide and grain boundaries present between the dielectric particles,
2. The dielectric composition according to claim 1, wherein when an average concentration of Ge in the dielectric particles is C1 mass % and an average concentration of Ge in the grain boundaries is C2 mass %, C1 and C2 satisfy a relationship of C1/C2>10. A dielectric element comprising the dielectric composition according to claim 1 or 2. An electronic component comprising a dielectric layer containing the dielectric composition according to claim 1 or 2 and an electrode.