JPH04164855A - Production of oxide superconductor - Google Patents

Abstract

PURPOSE:To obtain an oxide superconductor having a high superconducting transition temperature and excellent stability by subjecting a raw material powder mixture for producing a Y-Ca-Ba-Cu-O-based oxide superconductor to hot hydrostatic pressure treatment in a mixed atmosphere of an inert gas and an oxygen gas at a specific temperature. CONSTITUTION:Raw material powder for producing a Y-Ca-Ba-Cu-O-based oxide superconductor is mixed so as to give a composition shown by the formula (x is 0.001-0.5). Then the raw material powder mixture is subjected to hot hydrostatic pressure treatment in a mixed atmosphere of an inert gas and an oxygen gas at 850-1,100 deg.C to give an oxide superconductor containing the oxide shown by the formula. The prepared oxide superconductor has a superconducting transition temperature sufficiently higher than the temperature of liquid nitrogen and will not cause extraction of oxygen at a temperature during processing.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing a novel oxide superconductor,
Specifically, we manufacture oxide superconductors whose superconducting transition temperature (hereinafter sometimes simply referred to as Tc) sufficiently exceeds the liquid nitrogen temperature, and which has fewer problems such as fluctuations in Tc due to the release of oxygen during processing. It's about how to do it.

[Prior art] Three-layer perovskite RB is a typical oxide superconductor with Tc exceeding liquid nitrogen temperature (for example, 90 K).
a2CusOy (where R is one or more elements selected from the group consisting of Y or lanthanide series rare earth elements) has been discovered [^ppt, phys.

Lett, Vol. 51 (1987) P57].

However, the above-mentioned oxide superconductor has the property that the constituent oxygen atoms are easily extracted by the thermal influence during processing, and therefore the oxygen content changes depending on the heat treatment conditions during processing, etc. It is known that this phase transition causes an orthorhombic-tetragonal transition, and that Tc varies greatly in the range from OK to 90K [Phys,
Rev, B56 (19B?) P5719].

For example, RBa2Cu30. When a method (silver sheath wire method) is adopted in which powder is filled into a silver pipe, made into a wire by cold drawing, and then made into a superconducting wire by sintering heat treatment (800 to 900°C) of the powder part. However, there was a drawback that oxygen atoms were lost during the sintering heat treatment, resulting in deterioration of superconducting properties.

On the other hand, RB a 2Cu 40 s-type oxide is stable with no oxygen extraction even when heated to around 850°C, and its Tc is around 80, making it stable even when heated to around 850°C. It is attracting attention as an important substance from a practical point of view.

[Problems to be Solved by the Invention] By the way, the following two methods have been proposed as methods for manufacturing RBa2Cu40a type oxide superconductors.

(1) A method of heat-treating calcined powder in a high-pressure atmosphere of pure oxygen (for example, 930°C x 8 hours, oxygen pressure 100ate) [
Hyperbaric oxygen method; T c =81K.

Nature 33 [i (1988) P2S5-6
62 or Phys.

Rev, R39 (198B) P7347-7350
)1゜(2) A method of mixing calcined powder with a catalyst such as sodium carbonate and heat-treating it in an oxygen stream for a long time [normal pressure method;
T c =77K; Nature 338 (1
989) P32B-3301.

However, the inventors have confirmed through experiments that the methods (1) and (2) above have the following drawbacks.

In method (1), depending on the temperature and pressure conditions, RBaz
Cus 0t-6 phase or R2B a a Cu y O
It was found that the z phase etc. appeared, the amount of RBa2 Cu40a produced was extremely small, and the original characteristics of the RBaz Cua 06 phase were lost. In addition, method (2) tends to leave impurities in the product and requires a long time for heat treatment, making it unsuitable for practical application.

Not only that, but also RBazCu4OaBa Cu4O
Although it is said that a is higher than the liquid nitrogen temperature, the Tc is around 80 in both cases, and the liquid nitrogen temperature margin is too small, making it difficult to put it into practical use.Therefore, it is hoped that something with a higher Tc will be developed. ing.

The present invention was made in order to solve these technical problems, and its purpose is to provide a material that has a Tc sufficiently higher than the liquid nitrogen temperature and is stable enough to prevent oxygen from escaping at high temperatures during processing. The object of the present invention is to provide a method for manufacturing a superconductor.

[Means for Solving the Problems] The present invention that achieves the above object is defined as R (where R is 1 selected from the group consisting of Y and lanthanide series rare earth elements).
f! (the above elements), Ca, Ba.

A raw material powder mixture for producing an oxide superconductor consisting of Cu and O was heated to 850-1 in a mixed atmosphere of inert gas and oxygen gas.
By hot isostatic pressure treatment in a temperature range of 100°C, the oxidation represented by (R1-, ICa, l)B R2Cll4o8 (where, This is a method for manufacturing an oxide superconductor, the gist of which is to manufacture an oxide superconductor containing a substance.

[Function] The present inventors conducted studies from various angles in order to realize a stable electromotive conductor that has Tc sufficiently higher than the liquid nitrogen temperature and does not allow oxygen to escape even at high temperatures. Ta.

As a result, the three-layer perovskite RBa2Cu3Ot
In RBa, Cu4o, and type oxides in which the single curl in the type crystal structure becomes a double CuO chain, R of 0.
1 to 50 atom% was substituted with Ca (R1-1t Cax
) It has been found that the 882 C140B type oxide has a Tc sufficiently higher than the liquid nitrogen temperature and can be stably processed without oxygen extraction up to around 850°C. As a result of repeated studies on the specific manufacturing method, we found that R, Ca, Ba
.

A powder mixture consisting of Cu, O, etc. is subjected to hot isostatic pressing treatment (hereinafter sometimes referred to as HIP treatment) in a temperature range of 850 to 1100°C in a mixed atmosphere of inert gas and oxygen gas.
Then, the desired (Rs −* Ca, I) 11a2C
u40. They discovered that a type oxide superconductor could be obtained, and completed the present invention.

The HIP process in the present invention is a process in a mixed atmosphere of inert gas and oxygen gas, so if you want to achieve the same pressure (for example, 200 atm) with oxygen partial pressure as with pure oxygen, the total pressure as a mixed atmosphere For example, when the molar ratio of inert gas and oxygen is 1:1, the total pressure can be increased to 400 atm, and when it is 4:1, the total pressure can be increased to 1000 atm. Therefore, the diffusion of Cu atoms is further enhanced, and (R1-, Ca,) Ba2C
It is thought that the formation of u,06 type oxide superconductor is promoted. This is also a great advantage from the standpoint of operational safety, compared to increasing the total pressure with pure oxygen.

The temperature in the HIP treatment suppresses the formation of RBa2Cu30y type oxide, and (R1-X Caw )Ba2Cu
, from the viewpoint of promoting the production of 06 type oxide, it is necessary that the temperature is at least 850 ° C.
If the temperature exceeds 0°C, R2Ba4Cu and O□ are likely to be generated and miscible, so the upper temperature limit needs to be 1100°C.

- In the strength tree invention, (R1-*(:aJ BazCu
<The Oa type acid oxide Ca substitution amount (i.e. range of X) is 0.
The reason for setting it to 001 to 0.5 is as follows. That is, C
The effect of a substitution appears when X is 0.001 or more, and under the manufacturing conditions of the present invention, X is 0.5.
This is because it rarely exceeds. The preferred range is 0.001 to 0.2.

The composition of the raw material powder before HIP treatment of the present invention is not necessarily (
R+Ca): Ba: Cu=1:2:4 It is not necessary to set it to 4, and even if the composition deviates from this, it will be HI.
P treatment substantially reduces (tt+-xcax)tlar
It is sufficient if the cu406 phase is generated, but in order to stably generate this phase, the composition of the raw material powder must be changed (
R+Ca):Ba:Cu=1:2:4 is preferable.

Regarding the relationship between the HIP treatment process and the product forming process in the present invention, it is possible to (1) mix the raw material powder in advance, make it into a thin film or wire rod, and then perform HI Pfi to form a superconductor; After HIP treatment is performed to make a superconductor, it may be made into a thin film or a wire.

The present invention will be explained in more detail below with reference to examples, but the following examples are not intended to limit the present invention, and any design changes in accordance with the spirit of the preceding and following descriptions are within the scope of the present invention. It is included in the technical scope.

[Example] First, the basic structure of the oxide superconductor obtained by the method of the present invention, RBa, Cu40. The structure of is shown in Figure 1,
Conventional RBa, Cu30. The structure of the first
In the figure and FIG. 2, 1 is R, 2 is Ba, 3 is Cu,
4 indicates each 0 placed at the intersection of the line segments.

Oxide superconductor [(R+-
*Ca,)Ba2Cua 06 (x=0.o01
~o, s)] is RBa, in which a single CuO chain in the three-layer perovskite RBa2CusOy type crystal structure becomes a double CuO chain, as shown in Figure 1.
2CL1406 oxide in which 0.1 to 50 atomic % of R is replaced with Ca. In this structure with double CuO chains, a substance in which a part of R is replaced with Ca is subjected to HIPfi in a mixed atmosphere of inert gas and oxygen gas.
The greatest feature of the present invention is that it is manufactured by a process.

Example 1 Using each powder of Y2O,, Ho, Os, BaCO5゜CuQ, CaCo, with a purity of 99.9%, (R1-Ca,)
Ba2Cu40. (However, X in R=Y, H) is 0
,0.05.0.1 ,0.2 ,0.3 ,0.5
A raw material powder mixture was prepared and heated at 880℃ in air.
A calcination treatment was performed for 16 hours. After pulverizing the calcined powder, the total pressure was 1000 ats (oxygen partial pressure p02 = 200 atm) in a mixed gas atmosphere of Ar-80% and 0-20%.
at 830°C and 880°C.

HIP treatment was performed at each temperature of 930°C and 980°C for 10 hours.

The obtained powder was subjected to X-ray diffraction. Figures 3 and 4 show some of the results. Figure 3 shows Ya, e Caa,...
Bat Cu406 (980°C.

HIP), and Figure 4 shows H06,@@
Cao, osB az CL120g (930'C
.

HIP). The powder X-ray pattern in Figure 3 shows that the powder formation phase exhibits a YBa2Cu,O, type structure, and the powder X-ray pattern in Figure 4 shows that
The powder generation phase is YBaz Cu40. YBa with type structure
This shows that it contains a 2Cu307 type structure.

Further, the superconducting properties of the powder sample were measured using a vibrating sample magnetometer. Some of the results are shown in FIGS. 5 and 6. FIG. 5 shows Y, , Ca, .

It corresponds to Ba2 Cu4oa (980℃, HIP), and Figure 6 shows Hoo, esc ao, O5”
This corresponds to a2Cu4o6 (930°C, HIP). As is clear from these results, the (Rr-8Cax)Ba2Cu406 type oxide obtained in the present invention also exhibits a high Tc value.

Table 1 summarizes the results of powder X-ray diffraction and superconducting properties. In Table 1, RBa2 Cu40° type oxide [(Rr
-X Ca,) also includes Bat Cu406] to (1-2
-4) and can be considered from RBa2 Table 1 as follows. Although there are some differences depending on the type of R, the higher the HIP treatment temperature, the easier the formation of the (1-2-4) phase.
It can be seen that it is better to make the IP@embedding temperature as high as possible. Also, as the atomic ratio of Ca increases (1-2-4
) phase tends to be difficult to form, but as the atomic ratio increases, Tc also tends to increase.

[Effects of the Invention] As described above, according to the present invention, the superconducting transition temperature is sufficiently higher than the liquid nitrogen temperature, and oxygen does not escape at high temperatures during processing (R1-1t ea, )Baz
Cu4o6 type oxide superoxide superconductor.

[Brief explanation of the drawing]

Fig. 1 is a diagram for explaining the structure of RBaz Cu40g, Fig. 2 is a diagram for explaining the structure of RBaz Cu o7, and Fig. 3 is a diagram for explaining the structure of RBaz Cu40g.
(+, I A graph showing the powder X-ray diffraction pattern of Ba2Cu40a, FIG. 4 is a graph showing the powder X-ray diffraction pattern of HOo obtained by the present invention,
esCao, osBaz A graph showing the powder X-ray diffraction pattern of Cu406, Figure 5 is Yo, e Cao, +
Graph showing the superconducting properties of B R2Cua Oa, No. 6
The diagram shows HOo, *sCa o, osB a 2Cu4
2 is a graph showing the superconducting properties of No. 06. 1...R2...Ba 3...Cu 4...0 Applicant International Superconductivity Industrial Technology Research Center Figure 1 0-I YBa2Cu2O7 Figure 2 O discharge 1 YBa2Cu307

Claims (1)

[Claims] R (where R is one or more elements selected from the group consisting of Y and lanthanide series rare earth elements), Ca, Ba, Cu
A raw material powder mixture for producing an oxide superconductor consisting of ,O,
Under a mixed atmosphere of inert gas and oxygen gas, 850-110
By hot isostatic pressure treatment in the temperature range of 0℃, (R_1_-_xCa_x)Ba_2Cu_4O_8(
However, x is 0.001 to 0.5, and R has the same meaning as before.