JPH11322340A - Oxide superconductor and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce an oxide superconductor that contains the bismuth 2223 phase in a large proportion and can be produced in a short heat treatment time. SOLUTION: In the oxide superconductor that contains the bismuth 2223 phase including Bi, Pb, Sr, Ca and Cu as at least superconductive phase, the superconductive phase includes Ir. Or, in the oxide superconductor that contains the bismuth 2223 phase including Bi, Pb, Sr, Ca and Cu as at least superconductive phase and the non-superconductive phase, the superconductive phase or the non-superconductive phase includes Ir.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an oxide superconductor and a method for producing the same, and more particularly, to a superconductor containing a bismuth-based 2223 phase as a superconducting phase and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, an oxide superconductor containing Bi-Sr-Ca-Cu as a main component has a composition formula of Bi ₂ Sr ₂
A superconducting phase (bismuth-based 2223 phase) represented by Ca ₂ Cu ₃ O _M (M is a number close to 10) and a composition formula of Bi ₂ S
_{r 2 Ca 1 Cu 2 O N} (N is a number close to 8) superconducting phase represented by (bismuth-based 2212 phase) is known.

[0003] Among these phases, the bismuth-based 2223 phase has a high critical temperature and critical current density, and is considered to be the most suitable superconducting material for practical use among many oxide superconductors. R & D is underway.

When manufacturing an oxide superconductor containing a superconducting phase called bismuth-based 2223 phase, first, B
An oxide or carbonate of i, Sr, Ca, Cu is prepared. Next, this oxide or carbonate is powdered and mixed at a predetermined ratio to prepare a mixed powder. By heat-treating the mixed powder, an oxide superconductor containing a bismuth-based 2223 phase and a bismuth-based 2212 phase is obtained.

[0005]

In the conventional manufacturing method as described above, in addition to the bismuth-based 2223 phase, a bismuth-based 2212 phase having a low critical temperature and a low critical current density is also generated. There was a request to reduce the amount to increase the amount of bismuth-based 2223 phase formed.

[0006] To meet this demand, for example,
Zawa et al., “Formation of 2223 Phase and Variation in
 Composition of Bi (Pb) -Sr-Ca-Cu-O Superconductor
s ", Proceedings of the 2nd International Symposium
 on Superconductivity (ISS'89) pp.145-148,
By substituting a part of Bi with Pb, the composition formula becomes (Bi, Pb)
_TwoSr_TwoCa_TwoCu_ThreeO_MBismuth as represented by
A method for obtaining the system 2223 phase is described. using this method
Means that the ratio of bismuth-based 2223 phase is about 53% of the whole
There were few. Also, the sintering time was long.

Also, Nishida, "Formation behavior of high-temperature phase of Bi-based oxide superconductor", Sumitomo Metal Vol. 43-4 (1991) pp. 92-96
Also, the composition formula is (Bi, Pb) ₂ Sr ₂ Ca ₂ C
Another method for obtaining the bismuth-based 2223 phase represented by u ₃ O _M is described. Even in the method described in this document, the ratio of the bismuth-based 2223 phase was as low as about 30% of the whole. Further, the heat treatment time was also 100 hours, and a long heat treatment was required.

As described above, in the conventional method, the Bi system 22
There is a problem that the ratio of the 23 phases is small and a long heat treatment is required. Therefore, the present invention has been made to solve the above-described problem, and has been made in consideration of
It is an object of the present invention to provide an oxide superconductor having a high ratio of 23 phases and capable of being manufactured in a short heat treatment time.

[0009]

The present inventors conducted various experiments to increase the ratio of the bismuth-based 2223 phase and further shorten the heat treatment time. As a result, it was found that the presence of iridium (Ir) in either or both of the superconducting phase and the non-superconducting phase of the oxide superconductor increased the proportion of the bismuth-based 2223 phase and that the oxide superconductor could be manufactured in a short heat treatment time.

[0010] The reason is that iridium enters at least one of a superconducting phase or a non-superconducting phase such as a bismuth-based 2223 phase, stabilizes the bismuth-based 2223 phase, increases the proportion of the bismuth-based 2223 phase, and increases the heat treatment. It is considered that the time is shortened.

As a result of various experiments, it has been found that a part of iridium may be finely dispersed as a non-superconducting phase in the oxide superconductor, and may become a pinning center (pinning point) of the oxide superconductor. Was. Based on these findings, the oxide superconductor of the present invention provides an oxide superconductor containing at least a bismuth-based 2223 phase containing Bi, Pb, Sr, Ca, and Cu as a superconducting phase, wherein the superconducting phase contains Ir. It is characterized by the following.

Further, the oxide superconductor of the present invention is an oxide superconductor containing at least a bismuth-based 2223 phase containing Bi, Pb, Sr, Ca and Cu as a superconducting phase and a non-superconducting phase. The non-superconducting phase is Ir
It is characterized by including.

Further, the composition ratio (atomic ratio) of Bi in the bismuth-based 2223 phase is B, and the composition ratio (atomic ratio) of Pb is P
Assuming that the composition ratio (atomic ratio) of Ir is X, 0.023 ≦ X / (B + P + X) ≦ 0.0 between B, P, and X.
It is preferable that the relational expression represented by 68 be established.

Further, Ir is preferably present as an oxide. The composition formula of the oxide of Ir is Sr ₂ CaCuIr
It is preferably represented by O _Z (Z is a number greater than 0). Further, Z is preferably from 4 to 7, and more preferably Z is a number close to 5.

The average particle size of the Ir oxide is preferably 1.0 μm or less, more preferably 0.1 μm or less.

The method for producing an oxide superconductor according to the present invention is characterized in that at least Bi, Pb, Sr and C
In a method for producing an oxide superconductor containing a bismuth-based 2223 phase containing a and Cu and a non-superconducting phase, a raw material containing Bi, Pb, Sr, Ca, Cu, and Ir as starting materials It is characterized by using powder.

The composition ratio (atomic ratio) of Bi in the raw material powder is B, the composition ratio (atomic ratio) of Pb is P, and Ir
Assuming that the composition ratio (atomic ratio) of X is X, it is preferable that a relational expression represented by 0.023 ≦ X / (B + P + X) ≦ 0.068 is established between B, P, and X.

Preferably, Ir in the raw material powder exists as an Ir compound. Further, bismuth-based 222
Preferably, the Ir oxide is formed during the heat treatment to form or combine the three phases.

[0019]

A powder of Example (Example 1) Bi ₂ O _3, a powder of PbO, and the powder of SrCO _3, a powder of CaCO _3, C
A powder of uO and a powder of IrO ₂ were prepared. Bi and P
The composition ratio (atomic ratio) of b, Ir, Sr, Ca, and Cu is B
i: Pb: Ir: Sr: Ca: Cu = 1.8: (0.4
-X): The above-mentioned powder was mixed so that X: 2.1: 2.0: 3.0. At this time, the atomic ratio of Ir, that is, the Ir compounding amount (X) was set as shown in Table 1, and four kinds of mixed powders (Samples 1 to 4) were prepared as starting materials. For samples 1 to 4, the ratio of the atomic ratio of Ir (X) to the sum of the atomic ratio of Bi (B), the atomic ratio of Pb (P), and the atomic ratio of Ir (X) ｛X / (B + P
+ X)｝ was calculated.

[0020]

[Table 1]

In Table 1, "B" represents the atomic ratio of Bi (=
1.8), and “P” indicates the atomic ratio of Pb (= 0.4−
X).

For each of the samples 1 to 4, the mixed powder was sintered at a temperature of 780 to 790 ° C. and then pulverized by a ball mill. This powder was sintered at a temperature of 780 to 790 ° C. and then pulverized by a ball mill. Further, the powder was heat-treated at 820 ° C. for 20 hours in oxygen in order to reduce the amount of residual carbon in the powder. Thereafter, this powder was pulverized with a ball mill. Further, this powder was formed into a pellet having a diameter of 10 mmφ, and sintered in air at 835 ° C. for 80 hours.

The amount of bismuth-based 2223 phase formed in the oxide superconductor thus obtained was determined by a powder X-ray diffraction method. Specifically, the X-ray diffraction intensity I ₂₂₂₃ (115) of the (115) plane of the bismuth-based 2223 phase and the (11
5) The X-ray diffraction intensity I ₂₂₁₂ (115) of the plane was determined, and these values were substituted into the following equation to determine the amount V _H of formation of the bismuth-based 2223 phase.

[0024]

(Equation 1)

Atomic ratio X of Ir for samples 1 to 4
FIG. 1 shows the relationship between the amount of generated bismuth-based 2223 phase V _H
Shown in

"V _H " on the vertical axis in FIG. 1 is the amount of bismuth-based 2223 phase produced by the powder X-ray diffraction method.
It is almost equal to the volume ratio of the bismuth-based 2223 phase to the whole volume of the obtained oxide superconductor. That is, "V
If " _H " is 0.6, it indicates that the bismuth-based 2223 phase occupies 60% by volume of the oxide superconductor.

FIG. 1 shows that if the atomic ratio of Ir is increased, 80
It can be seen that a bismuth-based 2223 phase of 50% by volume or more was obtained in a short heat treatment time of as short as time. for that reason,
According to this method, it is found that an oxide superconductor having a high ratio of the bismuth-based 2223 phase and capable of being manufactured in a short heat treatment time can be obtained.

(Example 2) Sample 1 was prepared in the same manner as in Example 1.
A mixed powder as a starting material indicated by Nos. To 4 was prepared. The mixed powder was heated at a temperature of 780 to 7 for each of the samples 1 to 4.
After sintering at 90 ° C., it was pulverized with a ball mill. This powder was sintered at a temperature of 780 to 790 ° C. and then pulverized by a ball mill. This powder was heat-treated in oxygen at a temperature of 820 ° C. for 20 hours to reduce the amount of residual carbon, and then pulverized by a ball mill.

Further, each of the powders had an outer diameter of 8 m.
A silver pipe having a diameter of mφ and an inner diameter of 6 mmφ was filled and subjected to wire drawing until the outer diameter of the silver pipe became 1 mmφ. The drawn silver pipe was rolled to obtain a tape-shaped wire having a thickness of 0.2 mm. Each of the obtained tape-shaped wires was heat-treated at 830 ° C. for 60 hours in the air, and further subjected to press working at 830 ° C. for 30 hours. Each of the tape-shaped wires after the heat treatment was pressed and heat-treated at a temperature of 830 ° C. for 30 hours, and further pressed and heat-treated at a temperature of 830 ° C. for 30 hours to produce a superconducting wire including each of Samples 1 to 4.

In the obtained superconducting wire, the silver covering the oxide superconductor was peeled off, and the structure of the internal oxide superconductor was observed with a scanning electron microscope.

As a result of the observation, except for the oxide superconductor manufactured using Sample 1, bismuth-based 2223
Ir is dissolved in the crystal of the phase,
It was confirmed that oxide particles were scattered. 2223
Pb in the phase may be replaced by Ir.

As a result of analyzing the Ir oxide, the composition formula of the oxide was Sr ₂ CaCuIrO _Z (Z is a number exceeding 0), the maximum particle size of the Ir oxide was 0.5 μm, and the average The particle size was 0.1 μm or less. In addition, since Ir oxide is a non-superconducting phase, it may be a pinning center.

[0033]

According to the present invention, bismuth-based 2223
It is possible to obtain an oxide superconductor that has a large proportion of a phase and can be manufactured in a short heat treatment time.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between an atomic ratio X of Ir and a production amount V _H of a bismuth-based 2223 phase.

Continued on the front page (72) Inventor Kazuhiko Hayashi 1-3-1 Shimaya, Konohana-ku, Osaka-shi Sumitomo Electric Industries, Ltd. Osaka Works (72) Inventor Katsumi Kakimoto 2-37 Yagimotoyama-cho, Taishiro-ku, Sendai City, Miyagi Prefecture -7 Maison Alpha 103 (72) Inventor Hiroshi Maeda 35 Kawasaki Moto-Hasekura, Aoba-ku, Sendai City, Miyagi Prefecture 1-201 Kawauchi Residence

Claims (11)

[Claims] 1. An oxide superconductor containing at least a bismuth-based 2223 phase containing Bi, Pb, Sr, Ca and Cu as a superconducting phase, wherein the superconducting phase contains Ir. body. 2. An oxide superconductor containing at least a bismuth-based 2223 phase containing Bi, Pb, Sr, Ca and Cu as a superconducting phase and a non-superconducting phase, wherein the superconducting phase or the non-superconducting phase contains Ir. An oxide superconductor characterized by including. 3. The composition ratio (atomic ratio) of Bi in the bismuth-based 2223 phase is B, and the composition ratio (atomic ratio) of Pb is P.
Assuming that the composition ratio (atomic ratio) of Ir is X, 0.023 ≦ X / (B + P +) between B, P, and X.
The oxide superconductor according to claim 1, wherein a relational expression represented by X) ≦ 0.068 is satisfied. 4. The oxide superconductor according to claim 2, wherein Ir exists as an oxide. 5. The composition formula of an oxide of Ir is Sr ₂ CaCu.
The oxide superconductor according to claim 4, wherein the oxide superconductor is represented by IrO _Z (Z is a number exceeding 0). 6. The oxide superconductor according to claim 4, wherein the average particle diameter of the oxide of Ir is 1.0 μm or less. 7. The oxide superconductor according to claim 6, wherein the average particle diameter of the Ir oxide is 0.1 μm or less. 8. A method for producing an oxide superconductor containing at least a bismuth-based 2223 phase containing Bi, Pb, Sr, Ca and Cu as a superconducting phase and a non-superconducting phase, wherein Bi, Pb and Sr are used as starting materials. And Ca and Cu
And a raw material powder further containing Ir. 9. The composition ratio (atomic ratio) of Bi in the raw material powder is B, the composition ratio (atomic ratio) of Pb is P, and Ir
Assuming that the composition ratio (atomic ratio) of X is X, 0.023 ≦ X / (B + P + X) ≦ 0.
The method for producing an oxide superconductor according to claim 8, wherein a relational expression represented by 068 is satisfied. 10. The method for producing an oxide superconductor according to claim 8, wherein Ir in the raw material powder exists as an Ir compound. 11. The oxide superconductor according to claim 8, wherein an oxide of Ir is formed during the heat treatment for forming or bonding the bismuth-based 2223 phase. Manufacturing method.