JPH01164798A - Oxide superconductor and its production - Google Patents

Abstract

PURPOSE:To obtain the title superconductor having improved critical current density and causing no deterioration of critical temp. by calcining a powder mixture prepd. from starting materials weighed to provide a desired compsn. and then cooling the calcined powder mixture. CONSTITUTION:A material expressed by formula I obtd. from specified amts. of starting materials comprising an oxide of a rare earth element(abbreviated to RE bereunder) (e.g., Y2O3), BaCO3, CuO, etc., is mixed with a material expressed by formula II obtd. from starting materials comprising an oxide of the abovedescribed rare earth element, BaF2, and CuO, etc., in a proportion so as to provide a compsn. expressed by formula III (wherein 0.05<=x<=0.95), to obtain a powder mixture (wherein the content of S in the CuO to be used as a primary starting material of the powder mixture is regulated to 0.001-1%). The powder mixture is molded. After calcining the molded product at 925-980 deg.C for about 1-2hr, the product is cooled and then annealed appropriately, and cooled to about 200 deg.C. Thus, the title superconductor having a crystal structure combining many densely laminated blocks comprising plate single crystals expressed by formula IV, having >=1.1X10<3> A/cm<2> critical current density(at 0.15T) is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an oxide superconductor used, for example, in magnetic coil parts of magnetic levitation trains and particle accelerators, electronic devices, circuit boards of Josephson computers, etc. It is something.

[Prior art]

Currently, metallic superconductors such as Nb3Ge and Nb:+Sn are in practical use, but their critical temperature (Tc) is at most 23.2.

However, it has recently been announced that oxide-based superconductors made of a mixture of rare earth elements, alkaline earth elements, and copper oxide have significantly higher critical temperatures than metal-based superconductors (for example, a group from the University of Tokyo Faculty of Engineering It was announced at the American Physical Society that the temperature had been achieved at 90K), and it became possible to use inexpensive liquid nitrogen as a refrigerant instead of the expensive and cryogenic liquid helium (4,2 = -268,8 degrees Celsius). Therefore, great progress has been made in the prospect of practical application of this oxide-based superconductor in various application fields. Along with these publications, research is being actively conducted to further raise the critical temperature (Tc) of bulk or thin film oxide superconductors in the above-mentioned fields of application to room temperature.

[Problem that the invention seeks to solve]

In response to the demand for such oxide superconductors, improvements in their performance are required. In particular, in electronic applications and transportation systems, a high critical temperature (Tc, ) and a high critical current density (Jc) are required. However,
The current density of current oxide superconductors does not reach the level of current density required for electronics applications and transportation systems because the critical current density is lower than that of metal-based superconductors. Therefore, in order to utilize oxide superconductors in electronics, transportation systems, etc., there has been a problem in that the critical current density of oxide superconductors must be improved.

[Purpose of the invention]

The present invention aims to improve the critical current density (Jc) of the RE+BazCu:+07-♂-based oxide superconductor without deteriorating its critical temperature.

[Means for solving problems]

According to the present invention, RE+Ba2C113(1+-/ (
The critical current density Jc (0,15T) is 1.1 xlo'A/cm2, which has a crystal structure in which many blocks of densely laminated plate-like single crystals of RE=rare earth elements) are combined.
The above oxide superconductor is provided.

Further, according to the present invention, RIEIB82Cu3FX07-
/ (RE=rare earth element) system composition: 0.05≦x≦0
．． After firing the mixed powder which can be 95°C at 925-1050°C, preferably at 925-980°C for about 1-2 hours,
A method for producing an oxide superconductor is provided, which is characterized by rapid cooling.

That is, on the fracture surface of a sintered body with the composition RE1BazCu3Fx Or-/, crystals have grown into many densely stacked blocks, and fluorine compounds that are thought to exist in the grain boundary phase are pinning near the interface. It is thought that this plays an important role and contributes to improving the critical current density. And R
The sintered body having the composition of IK+BazC113F, 107-1' has a crystalline Mi texture in which densely laminated blocks are combined, so that the current density of the entire superconductor (bulk) is that of a general RE1 BazCu307-/ superconductor' (bulk) current density.

The smaller the size of the plate crystal, the better, but about 20 x 30
It is considered that the thickness is 6 μm or less, more preferably 4 μm or less.

Further, the density of the sintered body is preferably 4.5 g/cm'' or more.

A manufacturing method for obtaining such a superconductor (bulk) includes, for example, REJazCu307-/' + consisting of RE2O3+BaCO3, CuO as raw material powder, and REzO
:++ RE1BazCu+ consisting of BaFz and CuO
Ft07-/z are prepared and calcined at 850 to 950 degrees, respectively.

At this time, the sulfur in CuO of the raw material powder is 0.001
It is preferable that it is within the range of ~1χ. If the sulfur content in CuO is less than 0.0 prior χ, a block structure in which plate-like single crystals are densely stacked cannot be obtained, and if it exceeds 1χ, many impurities will precipitate in the crystal.

After that, RE+Ba2Cu3077 and RE1BazCu
3F407-/2 and RE+BazCusFo,
It is mixed and molded so that it becomes os~o, qs' 07-/. This molded body is fired in air at 925 to 1050°C, preferably 925 to 980°C, for a relatively short period of time, ie, 1 to 2 hours, then cooled, and then appropriately annealed and cooled to about 200°C. By such operations, R
E1BazCu30. -/A dense laminate of plate-like single crystals is produced. At this time, F (fluorine) is RE, Bazcu30
It has an auxiliary effect to make 7-/ into a plate-like single crystal,
It is thought that in the laminate, it is unevenly distributed at the grain boundaries of plate-like single crystals. Therefore, if F (fluorine) is less than 0.05, the plate-like single crystal will not grow in layers, and the normal RE+Ba
The critical current density is about the same as that of zCu307-/. F
If the (fluorine) content is more than 0.95, a large amount of BaF2 will precipitate, making it difficult to form a crystal structure of only the RE+BazCu+Ot-/composition, and the critical current density will deteriorate.

Also, if the calcination temperature is lower than 850℃, RE1BazCu+
Ot-/composition is not formed and the calcined powder does not become a superconductor.

When the temperature rises above 950°C, the solid solution progresses and the raw materials are eluted and RE+
The crystal structure of BazCu307-/composition mixture does not exist.

If the main firing temperature is lower than 925°C, the critical temperature will not become high. If the temperature is higher than 1050"C, it becomes completely in a solution state and is eluted, resulting in the formation of a RE+Ba2Cuz07-/composition mixture, which does not result in a superconductor. Furthermore, the superconductor phase can be stabilized by cooling after main firing.

Furthermore, further stabilization can be achieved by annealing during cooling after main firing.

In addition, in RE+BazCu307-/, RE, which is a rare earth element, includes Y (yttrium), Sc, La,
Ce, Pr+ Nd+Pm+Sm+Eu, Gd, T
b+Dy, Ilo, Er, Tm, Yb, Lu, and actinide elements are included.

〔Example〕

From Y2O39,09 mole χ, BaCO336,36 mole χ, and Cu054.55 mole χ (however, sulfur content is 0.015χ, purity 97.5χ), Y + BazC
While creating u307-/I, y2oi 9.0
9 mol χ, BaFz 36.36 mol χ and Cu0 5
4.55 mol χ (However, sulfur content 0.015'A
, purity 97.5X) and from Y1BazCIJ3Fa0
7-/'z was created.

These two reference raw materials Y, B'a2Cu307- /
After crushing r and Y, BazCu:+F407-/2, they were placed in an alumina or mullite ball and calcined in air at 900'C for 18 hours. Each calcined body was pulverized and mixed in a ratio of YlBazCuJO, 507-/, and formed into a pellet shape of 15 mmφ.

This molded body is fired in air at 925 to 1050°C, preferably 925 to 980°C, for 11 to 2 hours, then cooled and further heated in air at 580'C for 7 hours for 5 hours, and then heated to 200°C. Cool slowly, 7X4.5Xo
, 5 mm samples were obtained.

The change in resistance of this sample with respect to temperature was investigated using the four-terminal method, and the onceso ML degree (Tco) was 91K, and the offset temperature (Tce) was 87.5. Also, the density (
Archimedes method) was 5.2 g/cm3.

In addition, the M-11 hysteresis curve at 11K of the sample was determined using a vibrating sample break saw. These results are shown in FIG. Now, in the M-11 hysteresis curve, the difference in magnetization between the magnetization curve 1 and the demagnetization curve 2 (△
Formerly expressed as an expression; %expression%(). Here, μ0 is the magnetic permeability of vacuum, d is 1/2 of the thickness of the plate-shaped sample, and Jc is the critical current density. From the hysteresis curve in Figure 1, using the above formula, the difference in magnetization △H and νn The critical current density c was determined. As a result, the magnetization difference ΔM (0,15T) is 3°40 (
mT), and the critical current density Jc (0,15T) is 1.1
Xl0-'(8/cm").

Furthermore, the crystal structure of the sample was observed using an electron microscope, and a schematic diagram thereof is shown in FIG. As can be understood from FIG. 2, the crystal structure was such that a large number of blocks 8, in which plate-shaped single crystals a were densely stacked, were assembled in close contact with each other.

[Comparative Example 1] Y+Ba2Cu30□-/ with the same molar ratio as in the above example
After pulverizing only 1, it was placed in an alumina or mullite board and calcined, pulverized, molded and fired under the same conditions as in the previous example to obtain a sample of 11 x 11 x 1.3 mm.

This sample was similarly examined for resistance change with respect to temperature using the four-terminal method, and as a result, the on-cent temperature (Tco) was 91.5 and the off-cent temperature (Tce) was 89. Further, the density was 4.5 g/cm3. Furthermore, the M-11 hysteresis curve of the sample at 77K was determined using a vibrating sample magnetometer. These results are shown in FIG. From this hysteresis curve in FIG. 3, the magnetization difference ΔN and the critical current Jc were determined using the equations of the above embodiment. As a result, the magnetization difference ΔM(0,157) is 1.83 (mT),
The critical current density Jc(0,157) is 2.2Xl02(
8/cm2), which is understood to be significantly smaller than the above-mentioned embodiments of the present invention.

Furthermore, the crystal structure of the sample of the comparative example was observed using an electron microscope, and a schematic diagram thereof is shown in FIG. As can be understood from Fig. 4, the plate-like single crystal a ... is separated into pieces by 110
or have large grain boundaries G and are scattered in the structure,
Block 8 of the above embodiment is not configured. Therefore, it is thought that the current flow per unit area is small and the critical current density Jc is also small.

[Comparative Example 2] Same molar ratio of YBaCuO and YBaCuF as in the above example
I created O. However, the purity of CuO used in these was 99.9χ, and the sulfur content was 0.001% or less.

After pulverizing these two standard raw materials, they were placed in an alumina or mullite ball and calcined under the same conditions as in the previous example.
Grind, mold, and bake to 11 x 11 x 1.1mm
samples were obtained.

Similarly, this sample was examined for resistance change with respect to temperature using the four-terminal method, and as a result, the onset temperature (Tco) was 91 and the offset temperature (Tce) was 88. Also, the density is 5
．． It was 1 g/cm3. Furthermore, the 11 hysteresis curve of the sample at 77K was determined using a vibrating sample type force meter. These results are shown in FIG. From this hysteresis curve in FIG. 5, the magnetization difference ΔN and critical current density Jc were determined using the equations of the above embodiment. These results
The magnetization difference ΔM (0,15T) is 2.9 (mT), and the critical current density Jc (0,15T) is 4.2×102 (A/
cm2), which is understood to be significantly smaller than the above embodiments of the present invention.

〔Effect of the invention〕

In the present invention, the critical current density Jc can be improved without deteriorating the critical temperature of the RE+Ba2CuaO7-/based oxide superconductor.

[Brief explanation of the drawing]

Figure 1 shows Y1Ba2Cu3O7 in an embodiment of the present invention.
- / magnetization characteristic diagram, Figure 2 is the crystal structure diagram of the example sample, Figure 3 is the comparative example Y+BazCu:+Fo,
507-/, FIG. 4 is a single crystal structure diagram of the sample of Comparative Example 1, and FIG. 5 is a diagram of the magnetization characteristic of the sample of Comparative Example 2.

Claims (2)

[Claims] (1) RE_1Ba_2Cu_3O_7_-_δ(RE
= critical current density J that has a crystal structure in which a large number of densely laminated plate-like single crystals of rare earth elements) are combined.
An oxide superconductor whose c(0.15T) is 1.1×10^3A/cm^2 or more. (2) RE_1Ba_2Cu_3F_xO by calcination
＿7＿−＿δ (RE=rare earth element) based composition 0.05≦
A mixed powder that can satisfy x≦0.95 (however, 1 of the mixed powder
The sulfur content in CuO used as the next raw material is 0.001~
1%) is fired at 925 to 980°C for about 1 to 2 hours, and then cooled.