JPH06107497A - Superconducting fibrous crystal, single crystal and production thereof - Google Patents

Abstract

PURPOSE:To obtain a superconducting fibrous crystal of Bi2Sr2Ca2Cu3O10 having high critical temp. by burying the fibrous crystal of Bi2Sr2CaCu2O8 structure or the like into an oxide powder having a specific composition containing Li and heat treating. CONSTITUTION:A fibrous crystal composed of Bi, Sr, Ca, Cu and O and having Bi2Sr2CaCu2O8 structure (2212 phase) or a fibrous crystal composed of Bi, Sr, Cu and O and having Bi2Sr2CuO6 structure (2201 phase) is prepared. Next, the fibrous crystal is buried into the oxide power having the atomic composition ratio of Bi=1, Sr=0.5-1.5, Ca=1-3, Cu=1-5, Pb=0.2-1 and Li=0.05-0.25. Next, by heat-treating at 833-845 deg.C, the superconducting fibrous crystal having the atomic composition ratio expressed by the formula (wherein 0<x<0.4, 1.4<=y<=2, 0.01<z<0.1, 1.9<w<11) and Bi2Sr2Ca2Cu3O10 structure (2223 phase) is obtained.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a superconducting fibrous crystal, a single crystal and a method for producing the same.

[0002]

2. Description of the Related Art When the critical temperature (Tc) of a superconductor exceeds the temperature of liquid nitrogen, it has great significance in reducing cooling costs. Examples of the oxide superconductor whose critical temperature exceeds the liquid nitrogen temperature include Y-based, Bi-based, and Tl-based superconductors. Among these, in the Bi system, Bi ₂ Sr ₂ Cu
O ₆ phase (2201 phase), Bi ₂ Sr ₂ CaCu ₂ O ₈ phase (2212 phase) and Bi ₂ Sr ₂ Ca ₂ Cu ₃ O ₁₀ (2
223 phase), which are different from each other, and are also called 20K phase, 80K phase, and 110K phase, depending on the critical temperature of each. Of these, the 2223 phase with the highest critical temperature is
It is considered to be the most promising material for practical application of superconducting fibrous crystals and single crystals because of its low toxicity compared to Tl system and large temperature margin with liquid nitrogen temperature.

[0003]

The production conditions of the 2223 phase are very delicate, and there is a drawback that a mixed phase of 2223 phase and 2201 phase or 2212 phase is produced due to a slight change in the production conditions.

Therefore, the present inventor has developed a method for producing large single crystals of 2223 phase and fibrous crystals, and announced the method (Matsubara et al., Appl. Phys. Let.
t. , 58, 409 (1991)). This method is
P method (Conversion by Annealing)
In Powder), the method is called 220
1 phase or 2212 phase single crystal or fibrous crystal B
The single crystal or the fibrous crystal is crystallized while maintaining its original shape by embedding it in an oxide powder having an appropriate composition containing i, Sr, Ca, Cu and Pb and heat-treating the oxide powder at an appropriate temperature. This is a method in which the structure changes from 2201 phase or 2212 phase to 2223 phase, and large-sized 2223 phase single crystals and fibrous crystals can be produced.

However, 22 obtained using the CAP method described above
The critical temperature of the 23-phase single crystal or fibrous crystal was not yet sufficiently higher than the liquid nitrogen temperature.

It is an object of the present invention to provide a 2223 phase superconducting fibrous crystal and a single crystal which have a higher critical temperature and can be put to practical use.

[0007]

The present inventors have conducted various studies in order to achieve such an object, and as a result, increased the critical temperature by adding Li to a 2223 phase single crystal or fibrous crystal. The present invention has been completed by finding that the above can be achieved.

That is, according to the present invention, Bi, Sr, Ca,
Cu, Pb, consists Li and O, the composition ratio of the atoms _{Bi 2-x Pb x Sr y} Ca y Cu 3 Li z O w (0 <
x <0.4, 1.4 ≦ y ≦ 2.0, 0.01 <z <0.
1 and 9.0 <w <11.0), and Bi ₂
The present invention provides a superconducting fibrous crystal having a Sr ₂ Ca ₂ Cu ₃ O ₁₀ structure (2223 phase).

The present invention is also based on Bi, Sr, Ca, C.
It consists of u, Pb, Li and O, and the composition ratio of the atoms is Bi _2-x Pb _x Sr _y Ca _y Cu ₃ Li _z O _w (0 <x
<0.4, 1.4 ≦ y ≦ 2.0, 0.01 <z <0.
1 and 9.0 <w <11.0), and Bi ₂
The present invention provides a superconducting single crystal having a Sr ₂ Ca ₂ Cu ₃ O ₁₀ structure (2223 phase).

Further, the present invention provides (a) Bi, Sr, C
a, Cu and O, Bi ₂ Sr ₂ CaCu ₂ O
Fibrous crystals having ₈ structures (2212 phases), or B
i ₂ Sr ₂ CuO consisting of i, Sr, Cu and O
A fibrous crystal having ₆ structures (2201 phase) was used, and the composition ratio of (b) atoms was Bi = 1.0 Sr = 0.5 to 1.5 Ca = 1.0 to 3.0 Cu = 1.0 to 5.0 Pb = 0.2 to 1.0 Li = 0.05 to 0.25 embedded in oxide powder and heat treated at 833 ° C. to 845 ° C., atomic composition ratio Bi _{2-x
Pb x Sr y Ca y Cu 3} Li z O w (0 <x <0.
4, 1.4 ≦ y ≦ 2.0, 0.01 <z <0.1, and 9.0 <w <11.0), and Bi ₂ Sr ₂ C
The present invention provides a method for producing a superconducting fibrous crystal having an a ₂ Cu ₃ O ₁₀ structure (2223 phase).

Furthermore, the present invention provides (a) Bi, S
consisting of r, Ca, Cu and O, Bi ₂ Sr ₂ CaC
Single crystal having u ₂ O ₈ structure (2212 phase), or B
i ₂ Sr ₂ CuO consisting of i, Sr, Cu and O
A single crystal having ₆ structures (2201 phase) was prepared by using (b) atom composition ratio Bi = 1.0 Sr = 0.5 to 1.5 Ca = 1.0 to 3.0 Cu = 1.0 to 5 0.0 Pb = 0.2 to 1.0 Li = 0.05 to 0.25 embedded in an oxide powder and heat treated at 833 ° C. to 845 ° C., the atomic composition ratio is Bi _{2 -x
Pb x Sr y Ca y Cu 3} Li z O w (0 <x <0.
4, 1.4 ≦ y ≦ 2.0, 0.01 <z <0.1, and 9.0 <w <11.0), and Bi ₂ Sr ₂ Ca.
_{The present} invention provides a method for producing a superconducting single crystal having a ₂ Cu ₃ O ₁₀ structure (2223 phase).

A fibrous crystal and a single crystal composed of Bi, Sr, Ca, Cu and O and having a Bi ₂ Sr ₂ CaCu ₂ O ₈ structure (2212 phase), which are used for producing the superconducting fibrous crystal and the single crystal of the present invention. Crystals, Bi, Sr, C
It consists of u and O and has a Bi ₂ Sr ₂ CuO ₆ structure (22
The fibrous crystal and the single crystal having the (01 phase) can be produced by the method described in the following Document 1, Document 2 or Document 3.

Reference 1: Matsubara et al., Jpn. J. Appl.
Phys. , 28 , L1121 (1989) Reference 2: Matsubara et al. Cryst. Growth, 11
0 , 973 (1991) Reference 3: Kishida et al., J. Am. Cryst. Growth, 9
9 , 937 (1990) The length of the 2212 phase or 2201 phase fibrous crystal used in the present invention is about 3 to 15 mm, and the size of the single crystal is about 2 × 2 mm ² .

The powder for embedding the 2212 phase or 2201 phase fibrous crystal or single crystal has an atomic composition ratio of Bi = 1.0, Sr = 0.5 to 1.5,
Ca = 1.0 to 3.0, Cu = 1.0 to 5.0, Pb =
It is manufactured by mixing the raw materials so that 0.2 to 1.0 and Li = 0.05 to 0.25 and then firing. The raw material is not particularly limited as long as it can form an oxide by firing, and simple metals, oxides, various compounds (carbonates, etc.) can be used. As a raw material,
A compound containing two or more of the above atoms may be used. When firing is performed in an oxygen atmosphere such as in the air, or when the raw material itself contains a sufficient amount of oxygen, it is not necessary to use the raw material that serves as an oxygen source. The firing temperature and time are usually 800 to 860 ° C. and 5 to 100 hours, for example, 840 ° C. and 20 hours, although the firing temperature and time vary depending on the type of raw material used and the composition ratio. The firing means is also not particularly limited, and any means such as an electric heating furnace, a gas heating furnace, and a light heating furnace can be adopted. The fired product thus formed is sufficiently pulverized into powder. Next, this powder is embedded with a fibrous crystal or single crystal of 2212 phase or 2201 phase obtained by the method described in the above-mentioned literature and heat-treated. The heat treatment temperature and time differ depending on the composition ratio of the powder used, the size of the fibrous crystals and single crystals to be embedded, etc.
It is in the range of about 0 to 200 hours, and as an example, 84
150 hours at 0 ° C. The heat treatment means is also not particularly limited, and any means such as an electric heating furnace, a gas heating furnace, and a light heating furnace can be adopted. After the heat treatment is completed, the fibrous crystals or single crystals are separated and taken out from the powder to obtain Bi _{2-x.
Pb x Sr y Ca y Cu 3} Li z O w (0 <x <0.
4, 1.4 ≦ y ≦ 2.0, 0.01 <z <0.1, and 9.0 <w <11.0), and Bi ₂
Superconducting fibrous crystals and single crystals having the Sr ₂ Ca ₂ Cu ₃ O ₁₀ structure (2223 phase) can be obtained.

As will be described in detail in the following Examples, the 2223 phase superconducting fibrous crystals and single crystals of the present invention containing Li are 2223 phase superconducting fibrous crystals produced by the same method. The critical temperature rises by about 1K as compared with a single crystal. That is, it became clear that the addition of Li is effective in improving the critical temperature of the Bi-based 2223 phase.

In the manufacturing method of the present invention, it is essential to satisfy the following conditions (a) and (b).

(A) Use a powder having a composition ratio within a specific composition range; if even one composition ratio is out of the specified range, a 2223 phase fibrous crystal and a single crystal containing Li are added. Generation is difficult.

(B) heat treatment at a temperature within a specific range;
Even if all the compositions of the fired powder were within the specified range, if the heat treatment temperature was out of the specified range, Li was added.
The production of phase superconducting fibrous crystals and single crystals becomes extremely difficult.

The cause of the increase in the critical temperature due to the addition of Li in the present invention has not been fully clarified yet, but the following two possibilities are conceivable.

One possibility is the optimization of hole concentration. It is generally known that the critical temperature of an oxide superconductor has a correlation with the concentration of holes that are carriers.
That is, there is an optimum hole concentration that maximizes the critical temperature, and if the hole concentration is over or under the optimum value, the critical temperature decreases. Li addition 2 produced by CAP method
The reason why the 223 phase fibrous crystal and the single crystal have a higher critical temperature than the 2223 phase fibrous crystal and the single crystal not containing Li is that Li is useful for optimizing the hole concentration. To be

Another possibility is that the ratio of alkaline earth metals (Sr, Ca) has changed. In Bi-based superconductors, it is known that the ratio of Sr to Ca affects the critical temperature. The critical temperature tends to increase as the ratio of Sr having a large ionic radius increases. When converting from the 2212 phase or 2201 phase to the 2223 phase in the CAP method, it is also considered that the presence or absence of Li affects the ratio of Sr and Ca and the critical temperature rises.

[0022]

According to the present invention, Bi, Sr, Ca, C
It consists of u, Pb, Li and O, and the composition ratio of the atoms is Bi _2-x Pb _x Sr _y Ca _y Cu ₃ Li _z O _w (0 <x
<0.4, 1.4 ≦ y ≦ 2.0, 0.01 <z <0.
1, 9.0 <w <11.0) and Bi ₂ Sr ₂
Superconducting fibrous crystals and single crystals having a Ca ₂ Cu ₃ O ₁₀ structure (2223 phase) are obtained.

In the present invention, the addition of Li is based on Bi type 2223.
It has been revealed that it is effective in improving the critical temperature of the phase.
Considering the application in liquid nitrogen, a larger temperature margin can be taken, and thus a high critical current density can be achieved. Therefore, it is expected to be useful for improving the characteristics of magnetic field generating magnet materials that can be used in liquid nitrogen, and electric wire for electric power storage and electric power transportation.

[0024]

EXAMPLES Examples will be shown below to further clarify the features of the present invention.

The raw materials used as the respective atom sources used to prepare the powder for embedding in the CAP method in the following examples were as follows.

* Bi source Bismuth oxide (Bi ₂ O ₃ ) * Sr source Strontium carbonate (SrCO ₃ ) * Ca source Calcium carbonate (CaCO ₃ ) * Cu source Copper oxide (CuO) * Pb source Lead oxide (PbO) * Li Source Lithium carbonate (Li ₂ CO ₃ )

[0027]

Example 1 Bi ₂ Sr ₂ Ca ₄ Cu ₆ Pb _0.5 Li
After thoroughly mixing the raw materials to be the respective atomic sources so that the atomic composition ratio was _0.2 O _x , 15 g of the raw materials were placed in an alumina crucible and fired at 840 ° C. for 20 hours in an electric furnace. After crushing, it was baked again at 840 ° C. for 20 hours, and then the baked product was sufficiently crushed to obtain a powder for embedding in the CAP method.

Next, dozens of fibrous crystals having a 2212 structure were embedded in the above powder, and 830 each was placed in an electric furnace.
℃, 835 ℃, 838 ℃, 840 ℃, 843 ℃, 845
It heat-processed at 150 degreeC for 150 hours, and measured the transition of the magnetic susceptibility at each temperature. The results are shown in Fig. 1. In addition, each plot in FIG. 1 means the following samples.

 indicates the result of the sample in the above powder which was not heat-treated.

∘ indicates the result of the sample which was heat-treated at 830 ° C. in the above powder.

Δ is the result of the sample which was heat-treated in the above powder at 835 ° C.

▴ represents the results of a sample in the above powder which was heat-treated at 838 ° C.

□ represents the result of the sample which was heat-treated in the above powder at 840 ° C.

(3) is the result of a sample which was heat-treated at 843 ° C. in the above powder.

From the results shown in FIG. 1, the heat treatment temperature is 840 ° C.
It was confirmed that at 843 ° C., almost completely converted to 2223 phase. Moreover, when the heat treatment temperature is 845 ° C., the fibrous crystals cannot be separated from the powder. This is considered to be because as the heat treatment temperature increases, the liquid phase due to partial melting in the embedded powder increases and corrodes the fibrous crystals.

FIG. 2 shows changes in magnetic susceptibility with temperature near the critical temperature.

In FIG. 2, the black circles 22 do not contain Li.
23 shows a sample of structure 23.

◯ indicates a sample having a 2223 structure containing Li.

The sample (◯) to which Li was added was heat-treated at 840 ° C. For comparison, a sample not containing Li (●) is shown. This was created by the CAP method,
The embedded powder does not contain Li. Li
The critical temperature of the sample (◯) added with is 108.1K, and the critical temperature (10) of the sample without addition of Li (10) is
1.1K higher than 7.0K).

The relationship between the electric resistance of this fibrous crystal and the absolute temperature was measured by the DC four-terminal method. The results are shown in Fig. 3. As is clear from FIG. 3, the temperature at which the electric resistance became zero was 107.5K.

[0041]

[Example 2] The composition of the powder for embedding was set to Bi ₂ Sr ₂ Ca.
A fibrous crystal having a 2212 structure was heat-treated according to the method of Example 1 except that ₄ Cu ₆ Pb _0.5 Li _0.3 O _x was changed, and then this crystal was separated from the powder. In this case, at the heat treatment temperature of 838 to 840 ° C., almost 2
A sample converted to the 223 phase was obtained. Compared to Example 1,
The optimum heat treatment temperature decreased by about 3 ° C. Obtained Li addition 2
The critical temperature of the 223 phase fibrous crystal was 108.1 K, which was the same as in Example 1.

[0042]

Example 3 The composition of the embedding powder was Bi ₂ Sr ₂ Ca.
A fibrous crystal having a 2212 structure was heat treated according to the method of Example 1 except that ₄ Cu ₆ Pb _0.5 Li _0.4 O _x was changed, and then this crystal was separated from the powder. In this case, at the heat treatment temperature of 836 to 838 ° C., almost 2
A sample converted to the 223 phase was obtained. Compared to Example 1,
The optimum heat treatment temperature decreased by about 5 ° C. Obtained Li addition 2
The critical temperature of the 223 phase fibrous crystal was 108.2K, which was almost the same as in the case of Example 1.

[0043]

[Embodiment 4] The composition of the embedding powder was set to Bi ₂ Sr ₂ Ca.
A fibrous crystal having a 2212 structure was heat-treated in the same manner as in Example 1 except that ₄ Cu ₆ Pb _0.5 Li _0.5 O _x was used, and then this crystal was separated from the powder. In this case, at the heat treatment temperature of 833 to 835 ° C., almost 2
A sample converted to the 223 phase was obtained. Compared to Example 1,
The optimum heat treatment temperature dropped by about 8 ° C. Obtained Li addition 2
The critical temperature of the 223 phase fibrous crystal is 108.2K,
It was almost the same as in the case of Example 1.

[0044]

[Embodiment 5] The composition of the powder for embedding was set to Bi ₂ Sr ₂ Ca.
A fibrous crystal having a 2212 structure was heat treated according to the method of Example 1 except that ₄ Cu ₆ Pb _0.5 Li _0.1 O _x was changed, and then this crystal was separated from the powder. In this case, at the heat treatment temperature of 843 to 845 ° C., almost 2
A sample converted to the 223 phase was obtained. Compared to Example 1,
The optimum heat treatment temperature increased by about 2 ° C. Obtained Li addition 2
The critical temperature of the 223 phase fibrous crystal was 108.0 K, which was almost the same as in the case of Example 1.

[0045]

[Embodiment 6] The composition of the powder for embedding was set to Bi ₂ Sr ₂ Ca.
A fibrous crystal having a 2201 structure was heat-treated according to the method of Example 1 except that ₄ Cu ₆ Pb _0.5 Li _0.3 O _x was used, and then this crystal was separated from the powder. In this case, at the heat treatment temperature of 838 to 840 ° C., almost 2
A sample converted to the 223 phase was obtained. The critical temperature of the obtained Li-added 2223 phase fibrous crystal is 108.1K.
Was almost the same as the case of Example 1.

[0046]

[Embodiment 7] The composition of the powder for embedding is Bi ₂ Sr ₂ Ca.
A fibrous crystal having a 2201 structure was heat-treated according to the method of Example 1 except that ₄ Cu ₆ Pb _0.5 Li _0.4 O _x was changed, and then this crystal was separated from the powder. In this case, at the heat treatment temperature of 836 to 838 ° C., almost 2
A sample converted to the 223 phase was obtained. The critical temperature of the obtained Li-added 2223 phase fibrous crystal is 108.1K.
Was almost the same as the case of Example 1.

[0047]

[Embodiment 8] The composition of the powder for embedding was set to Bi ₂ Sr ₂ Ca.
A fibrous crystal having a 2201 structure was heat-treated in the same manner as in Example 1 except that ₄ Cu ₆ Pb _0.5 Li _0.1 O _x was used, and then this crystal was separated from the powder. In this case, at the heat treatment temperature of 843 to 845 ° C., almost 2
A sample converted to the 223 phase was obtained. The critical temperature of the obtained Li-added 2223 phase fibrous crystal is 108.0K.
Was almost the same as the case of Example 1.

[0048]

Example 9 A single crystal having a 2212 structure was heat-treated according to the method of Example 1, and then this crystal was separated from powder. In this case, at the heat treatment temperature of 840 to 843 ° C., a sample that was almost completely converted to the 2223 phase was obtained. The critical temperature of the obtained Li-added 2223 phase single crystal was 108.
1K was almost the same as in the case of Example 1.

[0049]

[Embodiment 10] The composition of the powder for embedding is Bi ₂ Sr ₂ C.
A single crystal having a 2212 structure was heat treated according to the method of Example 1 except that it was changed to a ₄ Cu ₆ Pb _0.5 Li _0.3 O _x , and then this crystal was separated from the powder. in this case,
222 at the heat treatment temperature of 838 to 840 ° C. almost completely
A sample converted into three phases was obtained. Obtained Li addition 22
The critical temperature of the 23-phase single crystal was 108.2K, which was almost the same as in the case of Example 1.

[0050]

Example 11 A single crystal having a 2201 structure was heat-treated according to the method of Example 1, and then this crystal was separated from powder. In this case, at the heat treatment temperature of 840 to 843 ° C., a sample that was almost completely converted to the 2223 phase was obtained. The critical temperature of the obtained Li-added 2223 phase single crystal was 10
The value was 8.1K, which was almost the same as in the case of Example 1.

[0051]

[Embodiment 12] The composition of the powder for embedding is Bi ₂ Sr ₂ C.
except changing the _{a 4 Cu 6 Pb 0.5 Li 0.3} O x was heat-treated single crystal having a 2201 structure in accordance with the procedure of Example 1, followed by separating the crystals and powders. in this case,
222 at the heat treatment temperature of 838 to 840 ° C. almost completely
A sample converted into three phases was obtained. Obtained Li addition 22
The critical temperature of the 23-phase single crystal was 108.2K, which was almost the same as in the case of Example 1.

[Brief description of drawings]

FIG. 1 is a diagram showing temperature dependence of magnetic susceptibility of a sample obtained at each heat treatment temperature.

FIG. 2 shows the temperature dependence of the magnetic susceptibility of a 2223 fibrous crystal added with Li in the vicinity of the critical temperature when 2223 without Li is included.
It is a figure compared with a fibrous crystal.

FIG. 3 is a diagram showing the relationship between the absolute temperature and the electrical resistance of the Li-added 2223 fibrous crystal obtained in the present invention.

Claims (4)

[Claims] 1. A composition comprising Bi, Sr, Ca, Cu, Pb, Li and O, the atomic composition ratio of which is Bi _2-x Pb _x Sr.
_y Ca _y Cu ₃ Li _z O _w (0 <x <0.4, 1.4 ≦
y ≦ 2.0, 0.01 <z <0.1, and 9.0 <w
<11.0) and Bi ₂ Sr ₂ Ca ₂ Cu ₃ O
A superconducting fibrous crystal having ₁₀ structures (2223 phases). 2. Composition of Bi, Sr, Ca, Cu, Pb, Li and O, the composition ratio of the atoms of which is Bi _2-x Pb _x Sr.
_y Ca _y Cu ₃ Li _z O _w (0 <x <0.4, 1.4 ≦
y ≦ 2.0, 0.01 <z <0.1, and 9.0 <w
<11.0) and Bi ₂ Sr ₂ Ca ₂ Cu ₃ O
A superconducting single crystal having ₁₀ structures (2223 phases). 3. A (2) Bi ₂ Sr ₂ CaCu ₂ O ₈ structure (2212) comprising Bi, Sr, Ca, Cu and O.
Phase) or a Bi ₂ Sr ₂ CuO ₆ structure (2201) composed of Bi, Sr, Cu and O.
(B) the composition ratio of atoms is Bi = 1.0 Sr = 0.5 to 1.5 Ca = 1.0 to 3.0 Cu = 1.0 to 5.0 Pb = 0.2-1.0 Li = 0.05-0.25 embedded in an oxide powder and heat-treated at 833 [deg.] C.-845 [deg.] C., wherein the atomic composition ratio is Bi2 _{-x.
Pb x Sr y Ca y Cu 3} Li z O w (0 <x <0.
4, 1.4 ≦ y ≦ 2.0, 0.01 <z <0.1, and 9.0 <w <11.0), and Bi ₂ Sr ₂ Ca.
_A method for producing a superconducting fibrous crystal having a ₂ Cu ₃ O ₁₀ structure (2223 phase). 4. A structure comprising (a) Bi, Sr, Ca, Cu and O, and having a Bi ₂ Sr ₂ CaCu ₂ O ₈ structure (2212).
Phase), or Bi, Sr, Cu and O
A single crystal having a Bi ₂ Sr ₂ CuO ₆ structure (2201 phase), the composition ratio of (b) atoms is Bi = 1.0 Sr = 0.5 to 1.5 Ca = 1.0 to 3. 0 Cu = 1.0 to 5.0 Pb = 0.2 to 1.0 Li = 0.05 to 0.25 embedded in an oxide powder and heat treated at 833 ° C. to 845 ° C. , The atomic composition ratio is Bi _{2-x
Pb x Sr y Ca y Cu 3} Li z O w (0 <x <0.
4, 1.4 ≦ y ≦ 2.0, 0.01 <z <0.1, and 9.0 <w <11.0), and Bi ₂ Sr ₂ Ca.
_A method for producing a superconducting single crystal having a ₂ Cu ₃ O ₁₀ structure (2223 phase).