JPH0465344A - Production of oxide superconductor - Google Patents

Abstract

PURPOSE:To obtain the superconductor having a high content of a high Tc phase and having high critical temp. and current density by forming a mixture of the sintered and crushed powder of specified composition having a low critical temp. and the powder having a high critical temp. in a specified manner and heat-treating the formed body. CONSTITUTION:The oxide-based raw material powders are mixed to obtain the composition of a Bi2Sr2Ca1Cu2Ox--based phase, sintered and crushed to prepare a first powder, and the oxide-based raw material powders are mixed to obtain the composition of a Bi2Sr2Ca2Cu3Oy-based phase for compensating the composition of the low-critical-temp. phase and sintered to prepared a second powder. The powders are then mixed, and the mixture is formed and sintered below the sintering temp. of the low-critical-temp. phase to obtain the desired Bi-based oxide superconductor contg. Pb.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a Bi Pb 5r-Ca-Cu-0 based oxide superconductor, specifically a Bi zsrz containing Pb.
ca, Cu: + Oy system, i.e. (Bi, Pb) 2
(Sr, Pb) B represented by zcazcus Oy
The present invention relates to a method for producing an i-based oxide superconductor.

(Prior art) Bi-Pb-5r-Ca-Cu-0 based oxide superconductor has a phase ((Bi, Pb)z(
Sr, Pb) zcalcu*o,, this (2223)
phase] and the low Tc phase ((Bi,Pb)z(Sr
, Pb)zCa+CuzOx - This is called the (2212) phase], and for high Tc, liquid nitrogen temperature (77K)
31. At a high value of 108, the resistance becomes 0Ω. On the other hand, in the low Tc phase, the resistance becomes 0Ω at 80Ω.

Therefore, the critical temperature changes depending on the mixing ratio of the high Tc phase and the low Tc phase, and the more the former is present, the higher the critical temperature becomes.

If a material with a high ratio for high Tc, for example, a material with a volume ratio of 95% or more, can be obtained, it can be put to practical use as a ring-shaped sintered body as a permanent magnet.

A conventional method for producing a Bi-Pb-5r-Ca-Cu-0 based oxide superconductor is as follows. That is, first ai, o,, Pbo, CaC0,,5rCO+, Cu2
Each powder of O (in the present invention, these are referred to as "oxide-based raw material powder") is Bi:Pb:Sr:Ca:Cu=0.8:
They are blended in a ratio of 0.2:0.8:1.0:1.4, and acetone is added as a grinding aid and mixed. The mixed powder is fired in the atmosphere at about 800° C. for about 110 hours, and the obtained powder is further pulverized. 5000 yen of this powder
It is molded into pellets at a pressure of about 8 kg/cm" and further
Sinter in air at 50-875°C for 10-50 hours. (For example, Japanese Journal
fApplied Physics, νol 28.
N (see 112, 1989, PP, L2182L2184) (Problem to be solved by the invention) B1-Pb-5r-Ca-Cu sintered by the above conventional method
In -0 series superconductors, the proportion for high Tc is around 80% by volume at most, and when examining temperature changes in resistance, the ratio for high Tc is around 80%.
It becomes 0Ω only around 4, and the superconducting transition width is wide. The reason for this is thought to be that the high Tc grains have not grown sufficiently.

An object of the present invention is to provide a method for producing a BiPb 5r-Ca-Cu-0 superconductor having a high ratio for high Tc and a high critical temperature.

(Means for solving problem i1) In the Bi-Pb-5r-Ca-Cu -0 based oxide superconductor, the reason why the volume ratio of high Tc does not exceed 95% is due to the formation temperature of high Tc. This is thought to be because the range is narrow and the production is anisotropic, resulting in a thin plate shape and a large amount of unreacted substances remaining.

When observing the MIG0 structure of a sample prepared using a conventional method,
Large particles of unreacted substances such as CazCuOff, CazPbOa, and CuO remain. As a result of examining the calcined powder and samples fired at various temperatures, it was found that there were no unreacted large particles in the calcined powder, but particles that grew and became larger during sintering. However, even if raw materials that have been blended at a composition ratio for high Tc from the beginning are sintered at a low temperature that does not cause grain growth of the unreacted phase, high Tc will not be produced. On the other hand, analysis of low-temperature sintered samples revealed that high Tc phase is low Tc phase (
2212) system and CazCuOz, CatPbOa, Cu
It was found that O etc. were generated by reaction.

Therefore, first, the raw materials blended to have a low Tc phase composition are sintered and pulverized at a relatively high temperature, and the remaining raw material (complemented with the low Tc phase composition) is added to the obtained low Tc phase powder to create a high Tc phase powder. It is expected that a high proportion of high Tc products will be produced if the raw materials (raw materials formulated to produce a high Tc content) are mixed and sintered at a relatively low temperature.

The present invention, which was made based on the above research results, is directed to a method for producing a high-ratio superconductor for high Tc, which is characterized by the following steps.

■ BizO,, Pbo, CaC01,5rC (h, C
Oxide-based raw material powders such as uO are mixed and sintered to have a (2212) phase composition to form a low Tc phase, that is, a (2212) phase.
) system oxide powder (this will be used as the first powder) is made.

■ Separately, the above-mentioned oxide-based raw material powder is blended with the above-mentioned first powder so as to have a composition for high Tc, that is, (2223), and fired. ).

■ The first powder and the second powder are mixed and molded, and the
Sinter at a temperature lower than the sintering temperature of

Through the above steps, a high ratio superconductor for high Tc can be efficiently obtained.

FIG. 1 is a process schematic diagram illustrating the method of the present invention. As shown in the figure, the method of the present invention involves manufacturing the first powder (low Tc phase powder) and the second powder separately. is a major feature.

Although the firing in (a) and the molding in (C) in the process shown in Figure 1 are not essential, it is necessary to increase the reactivity because carbonate is used as a raw material and a multi-component of four elements is used in the synthesis. It is desirable to carry out these steps as well. The firing temperature is preferably 700 to 800°C. A highly reactive low Tc phase is produced by the molding in (C) and the sintering in (d). The molding and sintering in (C) and (d) may be repeated two or more times with a pulverization step in between.

The firing in (b) is preferably carried out at 750 to 850'C.

If the temperature is lower than 150'C, carbonate will be difficult to decompose, and 85
At temperatures higher than 0°C, the particles become coarse and subsequent pulverization and mixing becomes difficult.

For example, the powders produced separately in the above steps are
: Mix at a ratio of 0.192 (IEI ratio).

This results in a composition ratio for high Tc (2223). This mixed powder is shaped (step (e)) and then sintered (
Step (f)).

Sintering in (f) is performed at 830-840'C. When sintering at 845°C, where the most (2223) phase is produced in the conventional method, the compounds in the second powder containing CazCu03 etc. become coarse.

(Function) In the normal sintering method in which oxide-based raw material powder is blended in a composition ratio that forms the (2223) phase from the beginning and then fired, the low Tc phase generated in the fired powder remains during the sintering process. (unreacted components) to form a light Tc phase.

However, at normal sintering temperatures, compounds consisting of unreacted components undergo grain growth, reducing the chance of reacting with the low Tc phase. This is the reason why the high Tc phase is difficult to generate.

However, if the low Tc phase is fired at the above temperature in advance, the low Tc phase will react more easily. Therefore, when the remaining components are mixed with this low Tc phase and sintered at a temperature lower than the normal temperature, grain growth of the compound consisting of the remaining components is suppressed and the high Tc phase is easily generated.

Below, a conventional method (comparative example) and an example of the present invention are shown,
The effects of the present invention will be specifically explained.

[Comparative example...conventional method] 8i, , +Pbo, axsr+, 7+caz,
+1Cux0,0)Bi2O3, so that Mi becomes
PbO, SrCO3, CaC0z, and CuO powders were blended and mixed. The blending ratio is shown in Table 1. This mixed powder was fired at 800'C in the air for 24 hours. 1 of this baked powder
It was compression molded to a size of 5 mmφ x 1 mmt and sintered at 845°C for 96 hours. As a result of X-ray diffraction, the amount of high Tc phase produced was 60
It was around % by volume. As a result of measuring the resistance-temperature characteristics of this sample using a four-terminal insect, it was found that the resistance was 0Ω at 104.

[Example 1] ■Preparation of first powder: BizOz, Pbo, 5rCO+, CaCO3, Cu
As shown in Table 1, O powder is Bi+, t+Pbo, iSr+, sCa+, 5Cu20
y (&[l composition I) and heated at 800'C.
After baking for 24 hours, it is crushed into 15mmφX1mmt
The samples were molded, sintered at various temperatures from 810 to 860°C for 24 hours, and pulverized as shown in Table 2. The first powder thus obtained was almost entirely a low Tc phase.

■Preparation of second powder: As shown in Table 1, the above raw material powder was converted into Pbo, +1Sro, z+cao, hacu+
Mix it so that it becomes Oy (!2) and heat it at 800°C.
A second powder was produced by firing for 4 hours and pulverizing. This powder was a mixture of CazPbO, CazCuO=, and CuO.

Table 2 ■ Production of sintered body The first powder obtained above and the second powder were mixed at a ratio of 1:0.192.
After mixing well at a weight ratio of , the mixture was molded into a size of 15 mm in diameter and 1 mm in length, and sintered at 835°C for 96 hours.

Table 2 shows the results of investigating the high Tc phase ratio and critical temperature of this sintered body.

From Table 2, the sintering temperature of the low Tc phase (!Ji formation 1) is 84
It can be seen that in the system at 0 to 860°C, the high Tc phase is 90% or more, and the Tc is 106.

(Margins below) Table 3 [Example 2] Using a powder obtained by sintering the first powder at 845°C for 24 hours with the same composition as in Example 1, it was mixed with the second powder and molded in the same manner as in Example 1. After that, sintering was carried out for 96 hours at various temperatures from 830 to 850'C as shown in Table 3. Table 3 shows the results of investigating the high Tc phase ratio and critical temperature of this sintered body. As a result, for samples fired at 830°C to 840°C, Tc =
IO2, which was found to be the ideal critical temperature for this material.

FIG. 2 is a temperature-electrical resistance curve of the comparative example, No. 3 of Example 1, and Nα3 of Example 2. The critical temperature of the comparative example is 104, while the critical temperature of the example is 106 and 107. Although this difference seems slight at first glance, there is a difference in the curve pattern as shown in FIG. 2, and this difference has a significant effect on the electrical characteristics.

The fact that the critical temperature is low and the rise of the curve is slow as in the comparative example confirms that the current path includes a phase other than the ideal superconducting phase.

(Effects of the Invention) According to the method of the present invention, a superconductor having a high proportion of Tc phase and a high critical temperature can be obtained. The method of the present invention can be widely applied to the production of various Bi-based oxide superconductors such as permanent magnets.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of the steps of the method of the invention. FIG. 2 shows temperature-electrical resistance curves of superconducting sintered bodies produced by the method of the present invention and the conventional method.

Claims (1)

[Claims] Oxide-based raw material powder is Bi_2Sr_2C with low critical temperature.
The first powder, which is blended, sintered and crushed to have a phase composition of a_lCu_2O_x system, and the same oxide-based raw material powder are used to supplement the composition of the phase with a low critical temperature to form a Bi_2Sr_2Ca_2Cu_3O_y system with a high critical temperature. A second powder is prepared separately, which is mixed and fired to have a phase composition of A method for producing a Bi-based oxide superconductor containing Pb, characterized in that the Pb-containing Bi-based oxide superconductor