JPS63295471A - Production of oxide superconducting material - Google Patents

Abstract

PURPOSE:To produce the title superconducting material having high density, uniform quality, and superior mechanical strength by molding a mixture of raw material oxides, sintering the molded product, then oxidizing the sintered product. CONSTITUTION:A molded body is obtd. by compacting a mixture of powder of raw material oxides with a press, etc. The molded body is calcined if necessary, and sintered at 950-1,100 deg.C, then oxidized at 800-920 deg.C to produce a laminar perovskite type oxide syperconducting material expressed by the formula: (A1-xBx)2CuO4 and (A1-yBy)6 Cu6O14 (wherein A is La, Y, Sc, or Yb; B is at least one kind selected from Ba, Sr, Ca, Pb, and Mg).

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing an oxide superconducting material exhibiting high-temperature superconducting properties useful for power transmission lines, magnet wires, and the like.

[Conventional technology]

Superconducting materials are obtained from various metals, alloys, compounds, oxides, etc., and are used or expected to be used in superconducting magnets, linear motor cars, power storage, etc. However, in these conventional superconducting materials, the critical temperature Tc at which electrical resistance becomes zero is low, and Nb3Ge, which is known to exhibit the highest Tc, has a temperature of only 23K (Kelvin), making it expensive to use liquid as a cooling medium. Due to problems such as the use of helium and the need for cryogenic equipment, development of its applications has been limited.

Recently, it has shown a high critical temperature of about 30 or higher (La+-x
5rx), which shows a high critical temperature of CuO4 system and about 90 (
A layered perovskite-type oxide superconducting material represented by the Y+-yBaV)bcuaO+n system was discovered, and theoretical analysis of its high critical temperature superconductivity phenomenon, crystallographic structural analysis, and its manufacturing method and application from a material standpoint. Research and development of laws and other fields is being actively carried out.

[Problem that the invention seeks to solve]

Regarding the oxide superconducting material, which is made of perovskite-type oxide and exhibits a high critical temperature, detailed studies have not yet been made on the specific heat treatment method used in the manufacturing method to obtain a compact with high density and uniform composition. . An object of the present invention is to provide a manufacturing method that solves the above problems.

[Means for solving problems]

The present invention provides the above-mentioned oxide superconducting molded body at temperatures ranging from 950°C to 110°C.
Sintering process at high temperature of 0°C and then 800°C
A two-stage heat treatment process including oxidation treatment at a temperature of ~920°C is characterized in that the oxide phase necessary to obtain high density and superconducting properties is obtained in the entire volume of the molded body. .

The present invention was achieved as a result of studies on various heat treatment methods in order to obtain the above-mentioned oxide superconducting material having high density and uniform composition. That is, the oxide raw material powder is prepared to have an appropriate composition, the molded body is compacted using a press, etc., and the molded body is heat-treated at various heating temperatures and heating atmospheres, and the phase state of the molded body is determined by superconducting properties and X-ray diffraction, etc. As a result of the investigation, some perovskites ((La10gSr6
．． +)zcuo4] and three-layer perovskite [represented by (Ye, 5sBao, 1s)icuaot] structures were found to be obtained in the temperature range between 800°C and 920°C. Ta.

Furthermore, in this case, only the very surface layer of the molded body becomes a layered perovskite type oxide during heat treatment in the normal atmosphere.
In order to form a layered perovskite oxide phase that is uniform throughout the inside of the molded product, long-term heat treatment of several tens of hours was required. By performing oxidation heat treatment inside
This made it possible to form a layered perovskite-type oxide phase to the inside of the molded body in a short period of time, within several hours.

Here, the oxidation treatment at 800°C or less requires a long treatment time to obtain the desired phase inside the molded body, and
Because the desired phase cannot be obtained at temperatures above 20°C,
Superconducting properties cannot be obtained. However, this 800℃
With oxidation heat treatment at ~920°C, sufficient sintering reaction does not occur and the density of the compact is low, resulting in insufficient mechanical strength.On the other hand, at temperatures above 950°C, atomic diffusion is promoted and sintering While the reaction occurs quickly, 1000
Partial liquid phase sintering also occurs from around 'C, resulting in a dense sintered body with sufficient strength. However, as mentioned above, 92
At temperatures above 0°C, a layered perovskite oxide phase exhibiting superconducting properties cannot be obtained.

Based on the above study results, the method for obtaining a high-density and uniform layered perovskite oxide superconducting material is to sinter the powder compact at a temperature range of 950°C to 1100°C, and then
It has been found that a heat treatment method in which oxidation treatment is performed in a temperature range of 0°C to 920°C is suitable. Here, the sintering temperature range of the first stage was limited to 950°C to 1100°C.
This is because the sintering reaction does not proceed sufficiently at temperatures below 1100°C, requiring a long treatment time, and at temperatures above 1100°C, complete melting occurs, damaging the shape of the compact. .

In the present invention, an oxide is used as the raw material powder for obtaining a molded body, but it is not necessarily limited to an oxide, and even if it is a carbonate compound, an aquatic compound, etc., the effect will not change in any way.

The details of the present invention will be explained based on the following examples [Example 1] Each powder of 101.6 g of yttrium oxide, 356.3 g of barium carbonate, and 215.3 g of cupric oxide as raw materials was weighed and placed in a ball mill. The mixture was milled, ground and mixed. This mixed powder was put into a mold and pressed to form a green compact, which was then heat treated in air at 900°C for 5 hours to undergo temporary sintering to decompose the barium carbonate.

Next, this pre-sintered body was crushed again in a ball mill and then press-molded to produce a molded body having a diameter of 301 m1φ and a height of 10 mm. This molded body was heat-treated in an oxygen atmosphere at a temperature of 600°C to 1150°C for 5 hours, then rapidly cooled to room temperature by blowing nitrogen gas, and the temperature dependence of electrical resistance, density, and X-ray diffraction measurements were performed. went. The results are shown in Table 1.

As is known from Table 1, the critical temperature T at which the electrical resistance becomes almost zero
c is observed when the oxidation treatment is performed at a temperature between 800° C. and 920° C. (Reference Examples 2, 3, and 4° 5), and is not observed at other treatment temperatures. Reference example 2 where Tc was observed,
3 and 4.5, it can be seen that most of them have a three-layer peropskite structure.

However, the density of the molded bodies of Reference Examples 1.2, 3, and 4.5 is low, and the value is almost the same as the density of the molded state, 2.7. On the other hand, Reference Example 6.7 treated at a temperature of 950°C or higher
In the case of , it can be seen that the density is high and sintering has progressed sufficiently.

In Example 1, after sintering heat treatment at 1000'C for 3 hours,
This is an example of the present invention in which oxidation heat treatment was further performed at 900° C. for 5 hours. It can be seen that in Example 1, a Tc of 91 was observed and at the same time a high density of 5.5 g/d was obtained. Note that Example 1 is an example in which the two-stage treatment of the present invention was performed on the compact after pre-sintering, but when the same two-stage treatment as in the example was performed on the green compact before pre-sintering. Also, Tc and 4 in 92
．． An oxide superconducting compact with a high density of 9 g/cd was obtained. However, higher densities can be obtained with compacts that have been pre-sintered.

In addition, in order to compare whether or not the three-layer perovskite phase is uniformly formed inside the compact, the compact after pre-sintering was
Heated in oxygen for 5 hours at 0°C, then 2° to room temperature.
Cooling was performed at a cooling rate of C/min.

The critical temperature of this reference example 9 is 91, and the density is 5.3 g/c.
d showed the same characteristics as Example 1, but as is clear from the X-ray diffraction diagram in Figure 1, the molded product of Example was a single phase, whereas the molded product of Example 1 was only slowly cooled from 1000°C. During processing, many different phases are present in the molded body. In other words, the surface of the compact is almost a three-layer perovskite phase, but the closer you get to the center, the more different phases there are, indicating that the oxidation reaction has not progressed sufficiently. The two-step heat treatment of treatment and oxidation treatment has high density and is suitable as a method for uniformly obtaining a three-layer perovskite phase to the inside of the molded body.

[Example 2] Lanthanum (La), yttrium (Y), scandium (Sc), yttrium (Yb), lead (pb),
CLa was prepared using copper (Cu) oxide powder and barium (Ba), strontium (Sr), calcium (Ca), and magnesium (Mg) carbonate powder.
o, qzsSro, ots) tcuOa (Example 2
), (Lag, qsro, oscao, as) g
cuon (Example 3), (Yo, 3Sco, +Bao
, 1) hc+Jio+4 (Example 4), (Yo, zYb
o, Jao, 1) icLliO+4 (Example 5), (Y
o, Jao, nPbo, x) icukOz (Example 6), (Yo, Jao, sMgo, +) hcuhO+4
(Example 7) were mixed to have the respective compositions, pre-sintered in the same manner as in Example 1, and then pulverized and press-molded to obtain a molded body. 5 hours,
Sintering was performed in air, and then at 900°C for 5 hours.
Oxidation treatment was performed in oxygen.

Table 2 shows the critical temperatures obtained for these molded bodies.

Sufficient density and high critical temperature were obtained even in the center of the compact.

Table 2 [Effects of the Invention] As explained above, the present invention has a two-step heat treatment process of sintering the molded body and oxidation treatment, thereby producing a high-density and uniform superconducting oxide phase. This method is suitable as a method for producing high critical temperature oxide superconducting materials with excellent mechanical strength.

[Brief explanation of drawings]

FIG. 1 is an X-ray diffraction diagram of the molded bodies obtained in Example 1 and Reference Example 9.

Claims (1)

[Claims] General formulas (A_1_-_xB_x)_2CuO_4 and (A_1_-_yB_y)_6Cu_6O_1_4 (where A is La, Y, Sc, Yb, and B is Ba, Sr,
In a method for manufacturing a layered perovskite-type oxide superconducting material represented by at least one selected from Ca, Pb, and Mg, raw material oxide powders are mixed, and after press molding, as it is, or after calcination, A method for producing a layered perovskite-type oxide superconducting material, which comprises performing a sintering treatment at a high temperature of 800 to 920°C, and then performing an oxidation treatment at a temperature of 800 to 920°C.