JPH01219057A - Oxide superconductor and its production - Google Patents

Abstract

PURPOSE:To obtain the subject superconductor with increased relative density and improved mechanical strength and critical current density by calcining a raw material contg. a rare-earth element and having a specified composition, and sintering the secondary raw material wherein the powder X-ray diffraction intensity ratio of the unreacted product is controlled to a specified value. CONSTITUTION:The raw powder or synthetic raw material having a composition shown by the formula (RE = rare-earth element) is calcined at 800-920 deg.C in the atmosphere or in oxygen, and the secondary raw material, wherein the powder X-ray diffraction intensity ratio of the unreacted product is controlled to 0.03<=I/I0<=3.0, is sintered to obtain the sintered superconductor. Since the plate crystal of the formula (preferably >=5mu) and crystallites of <=1mu size are mixed in the superconductor, the space between the plate crystals are filled with the crystallites, and a structure having a small number of pores is obtained. In addition, although the structure is densified, oxygen diffuses through the many grain boundaries consisting of crystallites, and hence the excellent characteristics of the superconductor reaches the inside of the sintered body.

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, and circuit boards of Josephson computers. It is something.

[Prior art and problems to be solved by the invention] Examples of oxide superconductors that are high-density bodies and exhibit a critical current density (Jc) of 103 A/co+2 or more include ATT, BE, etc.
L Laboratory is “Melt-Textured Grout”
Relative density 100χ obtained by h” (MTG) method
There are reports that superconductors with high critical current density (JC) were obtained using the MTG method, but in the MTG method, the sintered sample is melted at 1300°C in oxygen gas, then slowly cooled to room temperature, and then further heated to 900°C. This was not practical as it required an extremely complicated process of heating until temperature and then slowly cooling it overnight.

Therefore, efforts have been made to improve the relative density and critical current density by adjusting the powder and improving the calcination and main sintering conditions, but sufficient characteristics have not yet been obtained.

In view of the above points, the inventors of the present invention have conducted extensive research, and have developed a method for manufacturing ceramic materials, such as calcination and final firing, by controlling unreacted substances after calcination and optimizing the firing conditions. The relative density is easily over 95% and 1. I
X 10'A/cm" or more, preferably 1.6 X 1
It has been found that a critical current density of 0'A/cm'' or more can be obtained.

In the present invention, RE-Ba-Cu-0 system composition (RE
= rare earth elements), which are obtained by normal ceramic firing methods such as calcination and final firing, and their manufacturing method, which improves mechanical strength (three-point bending strength) and criticality by increasing its relative density. The purpose is to improve the current density Uc).

[Means for solving problems]

According to the present invention, REt Baz Cu5O4-/ (
It exhibits a crystal structure in which a plate-like single crystal of RE== rare earth element) and a minute single crystal of 1 μm or less are mixed, and if the plate-like single crystal is X and the minute single crystal is Y, the The area ratio of X and Y is X/Y≧0.05, the relative density is 95% or more, and the critical current density (Jc) is 1. lX10
An oxide superconductor is provided that is 3 A/cm2.

Also, REI Bag Cu, 0. - / (RE = rare earth element) mixed powder or synthetic raw material with a composition of 800 to 9
Calcined in air or oxygen at a temperature of 20°C, the unreacted product has a powder X-ray diffraction intensity ratio of 0.03≦I/Io≦3
．． A method for producing an oxide superconductor is provided, which is characterized by firing a secondary raw material kept in a range of zero.

That is, REI Baz Cu30? -/ (RE: rare earth element) plate-shaped crystal (preferably 5 μm or more) and 1 μm
Since microcrystals with a size of m or less are mixed, the microcrystals fill the spaces between the grains of the plate-like single crystals, resulting in a structure with few pores. As a result, the contact area between grains increases, and the critical current that can be passed per unit cross-sectional area, that is, the critical current density (Jc), increases. In addition, although this structure is dense, oxygen is diffused through many grain boundaries made of microcrystals, so that good superconducting properties can be obtained to the inside of the sintered body. When the plate-shaped single crystal is X and the minute single crystal is V, the area ratio of X and Y per unit area is X/Y≧0.05.
It is necessary that If X/Y <0.05, the above effect cannot be obtained. The manufacturing method for obtaining such a superconductor (bulk) is, for example, using REJs+ as a raw material powder.
BaCO3, CuO, etc. REt Baz Cu3
RE by powder mixed with 07-l, coprecipitation method, or sol-gel method.

A powder synthesized to have a composition ratio of Bag Cu1Ot−/
Calcinate 1 to 10 times in air or oxygen for 0 hours,
Maximum peak by powder X-ray diffraction of unreacted products such as BaC0:1 and CuO (1) and RFi+ Bat Cu
30. It is necessary to control the amount of unreacted products so that the intensity ratio of −/ to the peak (■.) of the (1,1,0) plane is in the range of 0.03≦I/Io≦3.0. be. I/Io
< 0.03, the REt Bat Cu1OyJ formation is sufficiently reacted and aggregated, and has grown to some extent after firing, so that fine particles as shown above cannot be obtained. Further, when I/Io > 3.0, the effect of calcination disappears. Also, if the calcination temperature is lower than 800℃, REI
Baz C1+30? -/The reaction of the composition hardly progresses, and when the temperature exceeds 920°C, CuO5YJaCu05 etc. Ejection occurs. Further, the calcination time is preferably 1 to 10 hours,
If the reaction time is shorter than 1 hour, the reaction will be insufficient, and if the reaction time is 10 hours or more, aggregation will begin to occur. The number of times of calcination may be any number of times, but 1
If the value is 0 to 1 or more, the effect will hardly change. In addition, in the main firing of the compact obtained by processing the powder produced by this calcination method, the initial set temperature (T) is set to 820, for example.
After raising the temperature to ~940°C, the density is further increased by raising the temperature to a maximum temperature (Tz) of 860~1020°C in air or oxygen at a heating rate of 0.1~4.0°C/hour. It becomes possible to further improve the critical current density (Jc). That is, in the firing pattern of constant temperature rise as described above, although some grain growth is promoted, the growth rate of fine grains is slow and they are left as they are to fill the air bubbles between the grains, resulting in densification.

Here, if the initial set temperature (T1) is lower than 820°C, the reaction will not occur and there will be no effect, and if it is higher than 940°C, the fine particles will grow larger than 1 μm and will not be densified, so the temperature increase rate will be 4.0°C. Preferably up to ℃/hour. Furthermore, if the maximum temperature (T2) is less than 860°C, sintering will be insufficient, and if it is higher than 1020°C, elution will occur.
A range of 1020°C is desirable.

〔Example〕

A mixed powder containing about 15% by weight of Y2O3, about 53% by weight of BaC0, and about 32% by weight of CuO was mixed in a wet rotary ball mill for about 24 hours, and this mixed powder was calcined in the air and dried in a mortar. The process of crushing was repeated several times.

This calcined powder was pulverized for about 50 hours in a wet rotary ball mill using an organic solvent (ethanol), and a molding binder (polyvinyl alcohol) was uniformly mixed with the resulting fine powder, and the powder was mixed with a molding binder (polyvinyl alcohol) at a concentration of about 1,000 g per 1 cm. The molded body was press-molded at a pressure of about 600 mm after main firing.
Heat treatment was performed in oxygen at ℃ to obtain sample pieces for each measurement shown in Table 1. Powder X-ray analysis was performed using the crushed powder after the final calcination, and comparisons were made at diffraction angles of 2θ: 20 to 60°. At this time, I/I. is the highest peak intensity of unreacted substances appearing in the powder X-ray diffraction pattern/RE+ Baz
This is the (1,1,O) main peak intensity of Cu307-/. The calcination conditions and main calcination conditions for obtaining the above sample pieces are shown in Table 2.

(Hereafter, blank) Table 1 Relative density (χ), critical current density (Jc), weather resistance, and bending strength were measured for each sample piece shown in Table 1 obtained above. Shown in the evaluation column of the table. The relative density is the bulk specific gravity/theoretical density by the Archimedes method, and the critical current density (Jc) is the actual value (0,047
(in a magnetic field), weather resistance was tested in a wet test (40°C
room temperature resistance ρ and bending strength (Mp
For a), the three-point bending strength was measured. In addition, the sample surface of each sample number was observed using a metallurgical microscope at a magnification of 800 times to observe the morphology of the structure and the area ratio of plate-like single crystals X and minute single crystals Y per unit area.

(Hereinafter, blank) As understood from Table 2, sample numbers 1 and 11 are outside the scope of the present invention, and both are calcined powder powder
Peak intensity ratio (I/I) in line diffraction.

) is out of the range of 0.03 to 3.0, the relative density is low, and the critical current density, resistivity, and bending strength are all poor. On the other hand, sample number 2-10.12-2
3 are within the scope of the present invention, and the relative density is 94.
% or more, critical current density (Jc) is 1110 or more, bending strength (Mpa) is 45 Mpa or more, especially sample number 2.
~10.14.16~21 Relative density is 95%
As mentioned above, the critical current density (Uc) is 1620 or more, the room temperature resistance value is 4.6 mΩ-cm or less, and the bending strength is 52.3 Mpa or more, which are excellent.

In addition, FIGS. 1 and 2 are reproductions of Mi weave photographs obtained by observing the sample surfaces of sample numbers 1 and 20 with a metallurgical microscope at a magnification of 800 times, and are within the scope of the present invention. As shown in Part 1, the structure is one around a plate-like single crystal.
It is surrounded by micro crystals of μm or less, exhibiting a dense structure with few pores, and the area ratio of plate-like single crystals X and micro single crystals Y per unit area is X/Y ≧ 0.05. Sample number 2-10.12-19.21-2 in Table 2
3 also has a similar crystal structure. On the other hand, the structure of sample number 1, which is outside the scope of the present invention, exhibits a structure consisting of uniformly grown grains V as shown in FIG.
The area ratio per unit area is X/Y<0.0
5, and there are many pores Z and it is not dense. Sample number 1
The same applies to 1.

〔Effect of the invention〕

As detailed above, the oxide superconductor of the present invention has RE+
The structure of the Bag Cu+07-/based oxide superconductor can be densified and the critical current density and bending strength can be improved, and the manufacturing method of the present superconductor is relatively easily reproducible and practical. .

[Brief explanation of the drawing]

Figure 1 is a replica of a metallurgical microscopic photograph of the surface of sample No. 20 in an example of the present invention magnified 800 times, and Figure 2 is a photograph of the same structure as in Figure 1 of sample No. 1 in an example. This is a copy of the figure.

Claims (2)

[Claims] (1) RE_1Ba_2Cu_3O_7_-_δ(RE
= rare earth element) exhibits a crystal structure in which a plate-like single crystal and a minute single crystal of 1 μm or less are mixed, and if the plate-like single crystal is X and the minute single crystal is Y, the X occupied per unit area is
, the relative density where the area ratio of Y is X/Y≧0.05 is 9
5% or more, critical current density (Jc) is 1.1×10^3A
/cm^2 oxide superconductor. (2) RE_1Ba_2Cu_3O_7_-_δ(RE
= rare earth elements) mixed powder or synthetic raw material with a composition of 8
Calcined in air or oxygen at a temperature of 00 to 920°C,
The powder X-ray diffraction intensity ratio of unreacted products is 0.03≦I/I
A method for producing an oxide superconductor, characterized by firing a secondary raw material kept in the range of _o≦3.0.