JP2806071B2 - 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 La-Ba-Cu oxides were found to exhibit superconducting properties, oxide superconductors have become Nb oxides.
Attention has been paid to the fact that Tc, which has been realized by an intermetallic compound superconductor represented by ₃ Sn, is drastically increased, and a Tc90K-class Y-Ba-Cu-based oxide superconductor (hereinafter referred to as Y System), Tc110K class B
i-Sr-Ca-Cu-based oxide superconductor (hereinafter sometimes abbreviated as Bi-based) or Tc120K-class Tl-Ba-Ca
-Cu-based oxide superconductors (hereinafter sometimes abbreviated as Tl-based) are known.

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),
It is said that c is about 75 to 80 K, and the high-temperature phase and the low-temperature phase are liable to coexist under general production conditions performed so far, and it is technically difficult to form a single-phase high-temperature phase.

It is known that substituting a part of Bi of a Bi-based oxide superconductor with Pb is effective in promoting the formation of a high-temperature phase, but does not act to improve Tc.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a method for producing a superconducting material capable of increasing the Tc of an oxide superconductor to a high temperature. Things.

[0006]

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 treated with a solution containing at least one of a compound having two or more enol hydroxyl groups, an alicyclic polyhydric alcohol compound, and an inorganic reducing compound.

[0007]

The oxide superconductor has a layered perovskite structure, and in some or some of the holes formed in the structure, electrons become carriers of superconductivity and dominate superconductivity. Is known to be.

[0008] The present inventors have determined that the superconducting carrier density and Tc
As a method of giving a change to the carrier density, the intermediate product in the oxide superconductor manufacturing process or one that has shown superconductivity has been particularly studied as one of the compounds having reducing properties. When treated with a solution containing one or more compounds having an enolic hydroxyl group, an alicyclic polyhydric alcohol compound or an inorganic reducing compound,
The present inventors have found that they effectively act on increasing the temperature of Tc, and have reached the present invention.

Although it has not been clarified sufficiently about the increase in the temperature of Tc, it is known that in the case of an oxide superconductor, the change in Tc is often correlated with the change in the C-axis length of the perovskite structure. The effect of the method of the present invention is clearly shown as a change in the C-axis length as described later. However, any compound having a reducing property is not applicable to the method of the present invention. If the reducing ability is too strong or too weak, it does not lead to an increase in the temperature of Tc, and an enol-based O having an appropriate reducing power is used.
It is limited to a compound having two or more H groups, an alicyclic polyhydric alcohol compound or an inorganic reducing compound.

The compounds having two or more enol hydroxyl groups include hydroquinone, hydrotoluquinone, catechol, pyrogallol, phloroglucinol,
Examples thereof include 2,4-benzenetriol, dihydroxynaphthalenes, and dihydroxyanthracenes.

The alicyclic polyhydric alcohol compounds include cyclopentanediol, cyclohexanediol, cyclohexadienediol and the like.

Examples of the inorganic reducing compound include metal hydride complex compounds such as sodium borohydride, lithium aluminum hydride and the like, hydrazine, diimide and the like. Sodium borohydride is NaBH ₄ , Na ₂ B ₂ H ₆ , Na ₂ B ₄ H ₁₀ , Na
It may be any of ₂ B ₅ H ₉ and the like related compounds.

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 typical case of producing a bulk oxide superconductor.

First, the metal element constituting the oxide superconductor preferably contains at least Bi, Sr, Ca, and Cu, and a part of Bi is replaced with Pb and a part of Sr is replaced with 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.

The production method characteristic of the present invention is to use a calcined molded product to reduce, among compounds having reducing properties, a compound having two or more enol hydroxyl groups, an alicyclic polyhydric alcohol compound or an inorganic compound. The treatment is to be performed with a solution containing any of the system-reducing compounds (hereinafter, also referred to as a treatment liquid), and then it may be dried. As the treatment method, a method of immersing the molded article in a treatment liquid is preferable,
In addition, a method of sprinkling the treatment liquid intermittently or continuously may be used.

The solvent constituting the treatment liquid is preferably a non-aqueous solvent in view of the stability of the superconductor, and examples thereof include methanol and toluene.

The production method of the present invention does not limit the concentration of the treatment solution, the treatment time and the temperature. However, in order to produce a homogeneous solution, the concentration of the treatment solution is set to 0.1 M or less and the treatment is carried out for a certain period of time. If the treatment is performed at room temperature, the treatment is preferably performed for 1 hour or more.
After the treatment, if necessary, washing is performed with a solvent such as methanol, and drying is performed. Drying conditions are not particularly limited, but gentle drying by ventilation at a low temperature is preferable.

The oxide superconductor manufactured through the above-described steps shows a change of a remarkable improvement in Tc as compared with the oxide superconductor manufactured by the conventional manufacturing method. Further, a clear change due to the manufacturing method of the present invention is that the length of the layered perovskite structure in the C-axis direction (hereinafter referred to as C
(Referred to as “axial length”), and it is considered that the change in the crystal structure and the electronic structure accompanying the treatment resulted in an improvement in Tc.

[0022]

EXAMPLE 1 and Comparative Examples _{1~3 Bi (NO 3) 3 ·} 5H 2 O, Sr (NO 3) 2, Ca (NO 3) 2 · 4H 2 O, Cu (NO 3) 2 · 3
Using commercially available H ₂ O reagent (Wako Pure Chemical Industries, purity 99.9%)
It was weighed so that the metal atom ratio became Bi ₂ Sr ₂ Ca ₁ Cu ₂ , mixed and stirred while heating, and the nitrate was gradually melted to form a uniform liquid. The uniform liquid was dried in a dryer at 230 ° C. for 20 hours, and then calcined in air at 800 ° C. for 10 hours to obtain a precursor. The powder obtained by pulverizing this precursor is approximately 15 m in diameter.
m, press molded into a disk shape of about 2mm thickness, 820 ℃ in air
For 20 hours. The molded product obtained at this stage was a conventional low-temperature phase Bi-based oxide superconductor, which was used as a test piece of Comparative Example 1.

The above molded product was immersed in a 0.1 M solution of hydroquinone in toluene at room temperature for 6 hours, and after leaching, washed with methanol for 1 hour and then dried at room temperature under ventilation to obtain a test piece of Example 1. Was.

Test pieces of Comparative Examples 2 and 3 were obtained in the same manner as in Example 1 except that toluene or methanol was used instead of the 0.1 M methanol solution of benzoquinone.

[0025] 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. Further, the C-axis length of the layered perovskite structure was determined by X-ray diffraction. The results are shown in Table 1.

[0026] Instead of Example 2 of hydroquinone, the resulting test pieces in the same manner as in Example 1 except for using the hydro Turki non, Tc _onset, T
c ₀ and C axis length were measured. The results are shown in Table 1.

Examples 3-6 Instead of a 0.1 M solution of hydroquinone in toluene, catechol, pyrogallol, 1,4-dihydroxynaphthalene or 3,5-cyclohexadiene-1,2-diol was used.
Except for using 0.1 M methanol solution to give a test piece in the same manner as in Example 1, Tc _onset, were measured Tc ₀ and C-axis length. The results are shown in Table 1.

Example 7 and Comparative Example 4 Bi (NO ₃ ) ₃ .5H ₂ O, Pb (NO ₃ ) ₂ , Sr (NO ₃ ) ₂ , Ca (NO ₃ ) ₂ .4H ₂ O, C
_{u (NO 3) 2 · 3H} 2 O commercial reagent (manufactured by Wako Pure Chemical Industries, Ltd., purity 99.5%) was used to weighed as ratio metal atom is _{Bi 1.5 Pb 0.5 Sr 2 Ca 2} Cu 3, heating While stirring, the nitrate was gradually melted to form a uniform liquid. The homogeneous liquid was dried in a dryer at 230 ° C for 20 hours, and then dried at 800 ° C in air for 10 hours.
After firing for a time, a precursor was obtained. The powder obtained by pulverizing this precursor is pressed into a disk having a diameter of about 15 mm and a thickness of about 2 mm,
It was calcined at 840 ° C. for 150 hours in an atmosphere having an oxygen partial pressure of 0.5 atm. The molded product obtained at this stage is a conventional high temperature phase Bi
This was a test piece of Comparative Example 4.

The molded article was immersed in a 0.1 M solution of hydroquinone in methanol for 6 hours at room temperature, extruded, washed with methanol for 1 hour, and then dried at room temperature under ventilation to obtain a test piece of Example 7. Was.

For the above two types of test pieces, _Tconset , T
c ₀ and C axis length were measured. The results are shown in Table 1.

[0031]

[Table 1]

Example 8 A molded article as a test piece of Comparative Example 1 was prepared by using 0.1% of hydroquinone.
Instead of immersing in M toluene solution for 6 hours, 0.1% NaBH ₄
Except that was immersed for 24 hours in M methanol solution to give a test piece in the same manner as in Example 1, Tc _onset, were measured Tc ₀ and C-axis length. The results are shown in Table 2.

Example 9 A molded article as a test piece of Comparative Example 1 was prepared by adding 0.1% of hydroquinone.
Instead of immersing in M toluene solution for 6 hours, use hydrazine
Except that was 0.01M in methanol solution soaking 6 hours (NH ₂ NH ₂₎ is to obtain a test piece in the same manner as in Example 1, Tc _onset, T
c ₀ and C axis length were measured. The results are shown in Table 2.

Example 10 A molded product as a test piece of Comparative Example 1 was prepared by adding 0.1% of hydroquinone.
Instead of immersing in a 6M toluene solution for 6 hours, LiAlH ₄
Except that 01MTHF solution was immersed 24 hours to obtain a test piece in the same manner as in Example 1, Tc _onset, were measured Tc ₀ and C-axis length. The results are shown in Table 2.

Example 11 Example 7 was repeated except that the molded article as a test piece of Comparative Example 4 was immersed in a 0.1 M methanol solution of NaBH ₄ for 24 hours instead of immersed in a 0.1 M solution of hydroquinone in toluene for 6 hours. Obtain a test piece in the same manner as
Tc _onset, it was measured tc ₀ and C-axis length. The results are shown in Table 2.

[0036]

[Table 2]

From the above results, according to the manufacturing method of the present invention, Tc is set to 10% for the Bi-based oxide superconductor in the low-temperature phase.
It is possible to raise the temperature to about K, and Bi
It can be seen that Tc can be raised to about 5K in the system oxide superconductor.

[0038]

As described above, according to the present invention, a method for increasing the Tc of an oxide superconductor can be provided.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) C01G 1/00-57/00 H01L 39/00-39/24 H01B 12/00

Claims (2)

(57) [Claims] 1. An intermediate product in a process for producing an oxide superconductor or a compound having superconducting properties, a compound having two or more enol hydroxyl groups, an alicyclic polyhydric alcohol compound or an inorganic reduction compound. A method for producing an oxide superconductor, comprising treating with a solution containing any of the reactive compounds. 2. The method for producing an oxide superconductor according to claim 1, wherein the intermediate product or an oxide having superconductivity is an oxide containing at least Bi, Sr, Ca and Cu.