JP2819883B2 - Method for producing thallium-based 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 superconducting material used in various superconducting applied devices and superconducting elements.

[0002]

2. Description of the Related Art At present, as a superconducting material, a metal / alloy superconducting material, a compound superconducting material and the like have already been put to practical use. Superconducting materials are used to make coils for superconducting magnets and electronic devices such as Josephson devices. In addition to the applications described above, applications to electronic computers that focus on the high-speed response and low power consumption of Josephson junctions are expected.

When considering the application of superconducting materials, it is desired that the superconducting transition temperature (Tc) be as high as possible. Metallic / alloy-based superconducting materials and compound superconducting materials must use expensive and rare liquid helium as a refrigerant, which is a factor that hinders the application of these superconductors to a wide range of fields. I have.

In this respect, copper oxide superconductors are far superior to conventional superconductors, and since the discovery of a Ba—La—Cu—O oxide superconductor having a Tc of 30 K,
90K class Y-Ba-Cu-O system, 110K class Bi-
Sr-Ca-Cu-O system, 120K class Tl-Ba-C
a-Cu-O system and the like have been discovered one after another. The discovery of a material having a Tc far above the temperature of liquid nitrogen has further increased expectations for a practical material.

[0005] Thallium-based superconductors have the highest Tc at present and are the most expected materials for practical use. In its application, it is desirable that the sample be homogeneous and free of foreign phases. In general, in order to obtain a homogeneous ceramic by the solid-phase reaction method, it is necessary to perform firing at a certain high temperature for a long time so that the raw materials react at a sufficient rate. However, in the Tl-based superconductor, since the constituent element Tl is very easily evaporated, the sample is wrapped in Au foil and fired to prevent the evaporation.

[0006]

If the firing time in the firing of the thallium-based superconductor becomes long, a reaction between the constituent element thallium and the Au foil starts to occur, so that it has been difficult to fire for a long time. . Therefore, an object of the present invention is to set T
An object of the present invention is to provide a method for producing a high-quality thallium-based superconductor that is homogeneous and does not contain a different phase by preventing a reaction between 1 and Au foil.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a method for manufacturing a thallium-based oxide superconductor, which comprises wrapping in a Ni-base heat-resistant alloy foil, wrapping in an Au foil and firing for a long time, and solid phase at a sufficient speed. It has been found that a high-quality sample can be obtained because the reaction between Tl and the Au foil is suppressed while the reaction proceeds.

[0008]

The examples EXAMPLES The following TlSr ₂ CaCu ₂ O _y in example illustrates the present invention.

As starting materials, thallium oxide (Tl ₂ O ₃ ) having a purity of 99% or more, strontium oxide (SrO),
Calcium oxide (CaO) and cupric oxide (CuO) were used, and each was weighed so as to have a predetermined compounding ratio. Next, the weighed ingredients are mixed well in a mortar and pressed to 10
A pressed body of mmφ × 1 mm was prepared. After wrapping this pressed body with a Ni-base heat-resistant alloy foil, further wrap it with Au foil,
Baking was performed at a temperature of 40 to 980 ° C for 30 minutes to 5 hours. The evaluation of the superconductivity was performed by a magnetic susceptibility measurement using a SQUID magnetometer and a normal DC four-terminal method. Powder X
The proportion and composition of the different phases were examined by line diffraction and EPMA.
Table 1 shows the ratio of the different phases of the obtained sample and the presence or absence of a reaction between Tl and the Au foil. For comparison, samples not wrapped with Ni-base heat-resistant alloy foil (sample numbers 4, 8, 9, 14, 15,
19, 20, 23) are also shown. It can be seen that by wrapping in a Ni-based heat-resistant alloy foil, the reaction between Tl and Au is suppressed, and the proportion of unreacted intermediate products is significantly reduced by firing for a long time. When the high-temperature baking is performed for 3 hours or more, the ratio of decomposition products from which Tl has escaped from the target composition increases. At a temperature of 940 ° C. or lower, the reaction rate is still slow, and at a temperature of 980 ° C. or higher, even a short time, the amount of scattered Tl cannot be ignored, which is not practical.

[0010]

[Table 1]

[0011]

According to the production method of the present invention, it is possible to obtain a Tl-based superconducting oxide which has been difficult to produce until now and has no heterogeneous phase, which is extremely useful for industrial applications of superconducting materials. .

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H01L 39/24 ZAA C04B 35/00 ZAAK

Claims (1)

(57) [Claims] 1. A method for producing a thallium-based oxide superconductor, comprising: wrapping in a Ni-base heat-resistant alloy foil, wrapping in an Au foil and firing.