JP3224578B2 - Manufacturing method of oxide superconductor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an oxide superconductor, and more particularly to a superconducting transition temperature (hereinafter referred to as Tc).
The present invention relates to a method for producing an oxide superconductor capable of increasing the temperature of a superconductor.

[0002]

2. Description of the Related Art Since it was revealed that La-Ba-Cu oxides exhibited superconducting properties, Y-Ba-Cu-based oxide superconductors (hereinafter sometimes abbreviated as Y-based), Bi -S
An r-Ca-Cu-based oxide superconductor (hereinafter sometimes abbreviated as Bi-based) and a Tl-Ba-Ca-Cu-based oxide superconductor (hereinafter sometimes abbreviated as Tl-based) are found one after another. Was done.

For example, the Bi system has a different Tc depending on the composition ratio of Bi, Sr, Ca, and Cu.
In the case of 2: 2: 3 (hereinafter referred to as high temperature phase), 105
Although Tc of about 110 K is shown, when the above composition ratio is, for example, 2: 2: 1: 2 (hereinafter referred to as a low temperature phase),
c is as high as 80K, and in some cases liquid nitrogen temperature (77K)
Is known to be much less than Also,
Under general manufacturing conditions, the high-temperature phase and the low-temperature phase are apt to coexist, and it is technically difficult to form a single-phase high-temperature phase.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and is intended to raise the Tc of an oxide superconductor to a high temperature.
An object of the present invention is to provide a method for producing a superconducting material capable of raising Tc to a temperature higher than the liquid nitrogen temperature even with the composition of c.

[0005]

Means for Solving the Problems A method for producing an oxide superconductor according to the present invention, which has achieved the above object, comprises an intermediate product in an oxide superconductor production process or a compound exhibiting superconductivity. Is to be immersed in an organic solvent at a temperature of 50 ° C. or higher.

As the organic solvent, aliphatic alcohols, aliphatic ketones, aliphatic aldehydes, aliphatic nitriles, and dimethyl sulfoxide are preferred. These organic solvents can obtain an optimum effect relatively stably. In addition, formamide, nitromethane and the like can be used.

[0007] The oxide superconductor that can be used in the manufacturing method of the present invention is not limited by the shape, and may be any of powder, bulk, wire, thin film and the like. Further, in producing a bulk oxide superconductor, the raw material powders are mixed, dried and molded, pre-sintered to obtain a precursor, and further sintered once or twice. Although a method for producing an oxide superconductor is generally used, an intermediate product after the above precursor may be applied to the production method of the present invention.

Hereinafter, the production method according to the present invention will be described with reference to a case where a bulk oxide superconductor is produced as a representative.

First, the metal element constituting the oxide superconductor preferably contains at least Bi, Sr, Ca and Cu, and a part of Bi is replaced by Pb and a part of Sr is replaced by La. Or the like. The raw material compound for supplying the metal element is not particularly limited. In addition to oxides, inorganic acid salts such as carbonates, nitrates and sulfates, acetates,
Organic acid salts such as oxalate, alkoxide compounds, complex compounds and the like are applicable.

The mixing method is not particularly limited.
For example, a known method such as mechanical mixing, a uniform solution method, and a coprecipitation method may be appropriately selected according to the type and physical properties of the compound.

The mixture comprising the starting compounds is dried if necessary and then fired. The firing is preferably performed at least twice with a pulverization molding step interposed therebetween, and the final firing temperature is preferably 800 ° C. or higher.

A production method characteristic of the present invention resides in that a baked molded article is immersed in an organic solvent at a temperature of 50 ° C. or higher. Even if the immersion treatment is performed at a temperature lower than 50 ° C., the effect of increasing the temperature of Tc is hardly observed. The high temperature side is not particularly limited as long as the organic solvent does not thermally decompose. In consideration of economy, it is usually sufficient to carry out at 250 ° C. or lower. In the case of an organic solvent having a boiling point of 50 ° C. or more, the method of immersion treatment under heating and reflux under normal pressure is the simplest. A method of immersion treatment by heating to 50 ° C. or more under pressure in a closed container may be used.

After the immersion treatment, the substrate is dried. Drying conditions are not particularly limited, but gentle drying by ventilation at a low temperature is preferable.

[0014]

The oxide superconductor manufactured through the above-described steps shows a change in that Tc is greatly improved as compared with the oxide superconductor manufactured by the conventional manufacturing method. It is considered that the mass transfer and the change in the electronic structure associated with the treatment resulted in an increase in Tc.

[0015]

EXAMPLES Example 1 and Comparative Example 1 Commercially available reagents of Bi ₂ O ₃ , PbO, SrCO ₃ , CaCO ₃ , and CuO (manufactured by Wako Pure Chemical Industries, purity 99.9%) were prepared using a metal atom ratio of Bi _1.8 Pb _0.2 Sr _2. Ca ₁ Cu
_The mixture was weighed to ₂ and mixed by a triturator, and then calcined in the air at 750 ° C. for 10 hours to obtain a precursor.
A powder obtained by pulverizing this precursor is applied to a powder having a diameter of about 15 mm and a thickness of about 2
It was press-formed into a disk having a diameter of mm and fired at 830 ° C. in the atmosphere for 24 hours. The molded product obtained at this stage is a conventional low-temperature phase B
It belongs to the i-based oxide superconductor. This was the test piece of Comparative Example 1.

The molded article was immersed in methanol for 28 hours under reflux with heating (65 ° C.), extruded, and dried at room temperature under ventilation to obtain a test piece of Example 1.

[0017] was measured superconducting transition initiation temperature (hereinafter referred to as Tc _onset) and zero resistance temperature (hereinafter referred to as Tc ₀₎ to the test strip by conventional four-terminal method. The results are shown in Table 1.

Example 2 Example 1 except that acetone was used instead of methanol.
A test piece was obtained in the same manner as described above. The temperature at the time of heating reflux is 57 ° C.
Met. Tc _onset of the resulting test piece was measured Tc _0. The results are shown in Table 1.

Example 3 The test piece of Comparative Example 1 was placed in a SUS pressure-resistant container, to which methanol was added, immersed and sealed. The vessel was heated and maintained at a liquid temperature of 180 ° C. for 3 hours. After the test piece was exposed, it was dried at room temperature under ventilation to give a test piece of Example 3.

Tc _onset and Tc ₀ of the obtained test piece were measured. The results are shown in Table 1.

Example 4 Example 3 except that acetone was used instead of methanol.
A test piece was obtained in the same manner as described above. Tc of the obtained test piece
_onset and Tc ₀ were measured. The results are shown in Table 1.

Example 5 Example 3 except that benzene was used instead of methanol.
A test piece was obtained in the same manner as described above. Tc of the obtained test piece
_onset and Tc ₀ were measured. The results are shown in Table 1.

Example 6 A test piece was obtained in the same manner as in Example 3 except that acetonitrile was used instead of methanol. T of the obtained test piece
C _onset and Tc ₀ were measured. The results are shown in Table 1.

Example 7 A test piece was obtained in the same manner as in Example 3 except that n-butyraldehyde was used instead of methanol. Tc _onset of the resulting test piece was measured Tc _0. The results are shown in Table 1.

Example 8 A test piece was obtained in the same manner as in Example 1 except that dimethyl sulfoxide was used instead of methanol and the immersion time was changed to 6 hours. The temperature at the time of heating to reflux was 189 ° C. Tc _onset of the resulting test piece was measured Tc _0. The results are shown in Table 1. Comparative Example 2 A test piece was obtained in the same manner as in Example 1 except that the immersion temperature was changed to 40 ° C. Tc _onset of the resulting test piece was measured Tc _0. The results are shown in Table 1.

Comparative Examples 3 to 7 Test pieces were obtained in the same manner as in Example 1 except that acetone, benzene, acetonitrile, n-butyraldehyde, and dimethyl sulfoxide were used instead of methanol, and the immersion temperature was 40 ° C. . Tc _{onset of} the obtained test piece,
Tc ₀ was measured. The results are shown in Table 1.

[0027]

[Table 1]

Example 9, Comparative Example 8 Bi ₂ O ₃ , SrCO ₃ , CaCO ₃ , and CuO commercially available reagents (purity 99.9%, manufactured by Wako Pure Chemical Industries) were mixed with Bi ₂ Sr ₂ Ca ₁ Cu ₂ having a metal atom ratio of The mixture was weighed so as to be mixed, mixed by a mill, and then calcined in the air at 750 ° C. for 10 hours to obtain a precursor. The powder obtained by pulverizing this precursor was pressed into a disk having a diameter of about 15 mm and a thickness of about 2 mm, and fired at 840 ° C. for 24 hours in the atmosphere.
The molded article obtained at this stage belongs to a conventional low-temperature phase Bi-based oxide superconductor. This was a test piece of Comparative Example 8.

The above-mentioned molded product was put in a SUS pressure-resistant container, methanol was added thereto, and the container was immersed and sealed. Heat the container,
The inside liquid temperature was kept at 180 ° C. for 3 hours. After the test piece was exposed, it was dried at room temperature under ventilation to give a test piece of Example 9.

The test pieces were measured for Tc _onset and Tc ₀ . The results are shown in Table 2.

[0031]

[Table 2]

[0032]

According to the production method of the present invention, the Tc of the oxide superconductor can be significantly increased, and especially in the Bi-based low-temperature phase composition, the Tc that reliably exceeds the liquid nitrogen temperature can be stably secured. .

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) C01G 1/00 C04B 41/82 CA (STN) JICST file (JOIS) WPI (DIALOG)

Claims (3)

(57) [Claims] 1. An oxide superconductor characterized by immersing an intermediate product or a material exhibiting superconductivity in a process of producing an oxide superconductor in an organic solvent at a temperature of 50 ° C. or higher. How to make the body. 2. The process for producing an oxide superconductor according to claim 1, wherein the intermediate product or the material exhibiting superconductivity is an oxide containing at least Bi, Sr, Ca and Cu. 3. The method for producing an oxide superconductor according to claim 1, wherein the organic solvent is a solvent selected from aliphatic alcohols, aliphatic ketones, aliphatic aldehydes, aliphatic nitriles, and dimethyl sulfoxide.