JPH0745357B2 - Superconducting fibrous single crystal and method for producing the same - Google Patents

Description

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

2. Description of the Related Art Since the discovery of high-temperature oxide superconductors in recent years, research and development for practical application have been actively conducted in various application fields.

More specifically, for example, SQUID (Superconducting Qua
For devices and devices such as computers using ntum interference devices) or Josephson devices, technology for thinning oxide superconducting materials is required.
Regarding this thinning, sputtering method, vapor deposition method, CV
It is reported that by the method D or the like, it is possible to manufacture a single crystal thin film having no grain boundary and having a characteristic that the critical current density exceeds 10 ⁶ A / cm ² and can be sufficiently put to practical use.

On the other hand, in order to apply it to electric power storage, electric power transportation, generation of strong magnetic field, etc., which takes advantage of the characteristics of oxide superconductor, it is necessary to convert it into a wire material. Method of filling in and re-heat treatment, sol-gel method,
Attempts have been made to suspend a powder of an oxide superconductor in a polymer solution and draw the wire, or to draw a wire from a melt of the oxide superconductor. However, since the wire rods obtained by these methods are all polycrystalline and have a low density and have grain boundaries, a wire rod having a practical level of properties has not been obtained. Further, such a wire has drawbacks such as brittleness, poor workability, and low bending strength, which are also characteristics of a polycrystalline body.

In addition, it has been reported that the critical temperature of some oxide superconductors exceeds the liquid nitrogen temperature, which has great significance in connection with cooling cost. Examples of such oxide superconductors having a critical temperature higher than the liquid nitrogen temperature include Bi type, Y type, and Tl type.

Bi system includes Bi ₂ Sr ₂ Cu ₁ O ₆ phase (2201 phase), Bi ₂ Sr ₂ CaCu ₂
There are three kinds of phases, O ₈ phase (2212 phase) and Bi ₂ Sr ₂ Ca ₂ Cu ₃ O ₁₀ phase (2223 phase).
Also known as K phase, 80K phase and 110K phase. In particular, the 2223 phase, which has the highest critical temperature, is considered to be the most suitable material for practical use because it has a large temperature margin with the liquid nitrogen temperature. However, there is a problem in that it is difficult to convert it into a mixed phase with the 2212 phase or 2201 phase. According to the solid reaction method, although a single phase of 2223 phase is achieved under strict composition control and firing atmosphere control, what is obtained is a powder or a polycrystalline sintered body, which has a low density. , Has many grain boundaries. Therefore, as in the case of 2201 phase and 2212 phase where large single crystals and single crystalline fibrous crystals have already been obtained, large single crystals of 2223 phase, single crystalline fibrous crystals, etc. are obtained. If so, it is extremely useful.

Means for Solving Problems As a result of various studies in view of the current state of the art, the present inventors have found that the Si ₂ Sr ₂ Cu ₁ O ₆ structure or the Bi ₂ Sr ₂ Ca ₁ Cu ₂ O ₈ structure is obtained. When fibrous single crystal having, Bi, Sr, Ca, when heat-treated under specific conditions in an oxide powder of a specific composition containing Cu and Pb, in the state of maintaining the initial fibrous crystal morphology, It was found that the crystal structure changed to Bi ₂ Sr ₂ Ca ₂ Cu ₃ O ₁₀ structure and the critical temperature rose above the liquid oxygen temperature.

That is, the present invention provides the following superconducting fibrous single crystal and a method for producing the same.

(1) Bi, becomes Sr, Ca, Cu, Pb, and O, the composition ratio of the _{atoms, Bi 2-x Pb x Sr} 1.9~2.1 Ca 1.9~2.1 Cu 3 O y (0 <x <0.4,10.0 <Y <11.0) and a superconducting fibrous single crystal having a Bi ₂ Sr ₂ Ca ₂ Cu ₃ O ₁₀ structure (2223 phase).

(2) Bi ₂ Sr ₂ Ca ₁ Cu ₂ consisting of Bi, Sr, Ca, Cu and O
A fibrous single crystal having an O ₈ structure (2212 phase), or composed of Bi, Sr, Cu and O, and having a Bi ₂ Sr ₂ Cu ₁ O ₆ structure (2201
A fibrous single crystal having a phase) is embedded in an oxide powder having 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 = 0.2 to 1.0, 830 to 860 The atomic composition ratio is characterized by being heat-treated at ℃, Bi _2−x Pb _x Sr _{1.9 to 2.1} Ca _{1.9 to 2.1} Cu ₃ O _y (0 <x <0.4, 10.0 <y <11.0), A method for producing a superconducting fibrous single crystal having a Bi ₂ Sr ₂ Ca ₂ Cu ₃ O ₁₀ structure (2223 phase).

The materials to be heat treated in the present invention are (a) Bi, Sr, C
a, Cu and O, and has a Bi ₂ Sr ₂ Ca ₁ Cu ₂ O ₈ structure (2212
(B) a fibrous single crystal having a phase) and (b) a fibrous single crystal composed of Bi, Sr, Cu and O and having a Bi ₂ Sr ₂ CuO ₆ structure (2201 phase). In the fibrous single crystals of (a) and (b), the Bi sites of the 2212 phase and 2201 phase may be partially replaced with Pb. These fibrous single crystals of (a) and (b) are both known and have a Bi ₂ Sr ₂ Ca ₁ Cu ₂ O ₈ structure (2212 phase) of (a).
The fibrous single crystal having
Ournal of Applied Physics Vol.28 (1989) L1121. The ( ₂ ) Bi ₂ Sr ₂ Cu ₁ O ₆ structure (2201
A fibrous single crystal having a phase) is disclosed by the present inventor on page 443 of the proceedings of the 1990 meeting of the Ceramic Society of Japan.

In producing the superconducting fibrous single crystal of the present invention, first,
As for atomic composition ratio, Bi = 1.00, Sr = 0.5 to 1.5, Ca = 1.
The raw materials are mixed so that 0 to 3.0, Cu = 1.0 to 5.0, and Pb = 0.2 to 1.0, and then baked. 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 the raw material, a compound containing two or more of the above atoms may be used. When the melting is carried out 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 as the oxygen source. The firing temperature and time vary depending on the type of raw material used, composition ratio, etc., but are usually in the range of about 800 to 860 ° C. and in the range of about 5 to 100 hours.
It is about 20 hours at ℃. The firing means is not particularly limited, and any means such as an electric heating furnace and a gas heating furnace can be adopted. Next, the formed fired product is sufficiently crushed and pulverized.

Then, the fibrous single crystal of (a) or (b) is embedded in the oxide powder (hereinafter sometimes referred to as an embedding powder) obtained above and heat-treated. The heat treatment temperature and time vary depending on the composition ratio of the embedding powder used, the size of the fibrous single crystal to be heat treated, etc., but are usually within the range of about 830 to 860 ° C. for about 50 to 200 hours, and as an example, 840
It is about 120 hours at ℃. The heat treatment means is also not particularly limited, and an arbitrary one such as an electric heating furnace, a gas heating furnace, a light heating furnace or the like can be adopted.

After the heat treatment is completed, the composition to be Bi _2-x Pb _x Sr _{1.9 to 2.1} Ca _{1.9 to 2.1} Cu ₃ O _y (0 <x <0.4, 10.0 <y <11.0) is obtained by taking out the object to be heated from the embedded powder. A superconducting fibrous single crystal having a Bi ₂ Sr ₂ Ca ₂ Cu ₃ O ₁₀ structure (2223 phase) is obtained. The length and shape of this fibrous single crystal are the same as those before the heat treatment.

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

(A) Use an embedding powder having a component ratio in a specific composition range; if the composition of the oxide powder used for embedding is out of the specified range, even if one kind of oxide powder is used, a fibrous single crystal
2223 phase conversion becomes difficult or impossible.

(B) heat treatment within a specific temperature range; even if all the compositions of the fibrous single crystal and the embedding powder are within the specified range, if the heat treatment temperature is outside the specified range, the fibrous single crystal Phase conversion of 2223 is still difficult or impossible.

In the method of the present invention, the mechanism by which the 2201 phase fibrous single crystal or the 2212 phase fibrous single crystal becomes the 2223 phase has not been fully clarified yet, but it is presumed to be as follows. 2201 phase fibrous single crystal or 2212 phase fibrous single crystal 22
The 23-phase formation requires the supply of Ca and Cu (and Pb when these fibrous single crystals do not contain Pb). In the method of the present invention, the heat treatment temperature (830 to 860 ° C.) of the fibrous single crystal in the oxide powder used for embedding corresponds to the partial melting temperature of the powder. If the heat treatment temperature is too high, the liquid phase portion of the oxide powder increases and the fibrous single crystal and the oxide powder are fused, so the fibrous single crystal should be separated from the oxide powder and taken out. Will be difficult. On the other hand, when the heat treatment temperature is lower than the partial melting temperature of the oxide powder, the interaction between the fibrous single crystal and the oxide powder does not occur, and thus the 2223 phase conversion is not achieved. However, when performing heat treatment in the above temperature range, a suitable liquid phase exists in the vicinity of the fibrous single crystal, and Ca and Cu from the oxide powder for embedding to the fibrous single crystal through this liquid phase. Is supplied,
It is thought that 2223 phase conversion will be achieved.

EFFECTS OF THE INVENTION According to the present invention, the composition is Bi _2−x Pb _x Sr _{1.9 to 2.1} Ca _{1.9 to 2.1} Cu ₃ O _y (0 <x <0.4, 10.0 <y <11.0), and Bi ₂ Sr ₂ A superconducting fibrous single crystal having a Ca ₂ Cu ₃ O ₁₀ structure (2223 phase) is obtained.

Since the superconducting fibrous single crystal of the present invention has a critical temperature of more than 100K, it can be used in liquid nitrogen. It also has the characteristic of being bendable. Therefore, by forming a wire by spot welding using laser light, etc., as a high-temperature superconducting material that can be used in liquid nitrogen, it is applied to a magnetic material generating magnetic material, a wire storage material for power storage and power transportation, and Is expected to be used in a wide range of fields such as point contact Josephson device materials using the tip shape.

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

Example 1 After sufficiently mixing the starting materials so that the atomic composition ratios shown in Table 1 below were obtained, 15 g of the starting materials were placed in an alumina crucible and fired at 840 ° C. for 20 hours in an electric furnace to obtain a fired product. Was sufficiently pulverized to obtain an oxide powder for embedding.

Then, as shown as a schematic cross-sectional view in FIG. _1, Bi ₂ Sr ₂ Ca ₁ Cu prepared in advance in the oxide powder for embedding (2) placed on an alumina boat (3). ₂ O ₈ structure (22
50 fibrous single crystals (1) having 12 phases) were embedded and heat-treated in an electric furnace at 840 ° C for 120 hours.

After the heat treatment was completed, the fibrous single crystal and the embedded powder were separated.

The X-ray diffraction pattern of the recovered fibrous single crystal is shown in FIG. From this X-ray diffraction pattern, it was confirmed that the fibrous single crystal after the heat treatment had the Bi ₂ Sr ₂ Ca ₂ Cu ₃ O ₁₀ structure (2223 phase).

Further, the relationship between the electric resistance and the absolute temperature of this fibrous single crystal measured by the DC four-terminal method was as shown in FIG. The temperature at which the electric resistance became zero was 107K.

The raw materials for manufacturing the oxide powder for embedding used in this example and 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 ... oxide cylinder (CuO) * Pb source ... lead oxide (PbO) Examples 2 to 6 According to the method of Example 1, fibrous single crystals having a 2212 phase structure or a 2201 phase structure shown in Table 1 were embedded in oxide powder and heat-treated at a predetermined temperature for 120 hours in an electric furnace.

It was confirmed that each of these fibrous single crystals after the heat treatment had the same crystal structure and superconductivity as those of Example 1.

Regarding Examples 1 to 6, Table 1 shows the phase structure of the fibrous single crystal before the heat treatment and the composition of the oxide powder, and Table 2 shows the heat treatment temperature, the structure of the fibrous single crystal after the heat treatment, and the critical temperature. Show.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an outline of heat treatment of a fibrous single crystal in the present invention. FIG. 2 is a drawing showing an example of the X-ray diffraction pattern of the fibrous single crystal obtained by the present invention. FIG. 3 is a drawing showing the relationship between the absolute temperature and the electric resistance of the fibrous single crystal obtained by the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Tomoji Kawai 5-26-15-615 Onohara East, Minoh City, Osaka Prefecture (56) References JP-A-4-46050 (JP, A) JP-A-3-150208 (JP, A) JP-A-3-12313 (JP, A) JP-A-63-307115 (JP, A)

Claims (2)

[Claims] 1. Composition of Bi, Sr, Ca, Cu, Pb and O, the atomic composition ratio of which is Bi _2-x Pb _x Sr _{1.9 to 2.1} Ca _{1.9 to 2.1} Cu ₃ O _y (0 <x <0.4. , 10.0 <y <11.0), and a superconducting fibrous single crystal having a Bi ₂ Sr ₂ Ca ₂ Cu ₃ O ₁₀ structure (2223 phase). 2. Bi ₂ Sr ₂ consisting of Bi, Sr, Ca, Cu and O.
A fibrous single crystal having a Ca ₁ Cu ₂ O ₈ structure (2212 phase) or composed of Bi, Sr, Cu and O, and having a Bi ₂ Sr ₂ Cu ₁ O ₆ structure (2201
A fibrous single crystal having a phase) is embedded in an oxide powder having 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 = 0.2 to 1.0, 830 to 860 characterized by a heat treatment at ° C., the composition ratio of atoms, a _{Bi 2-x Pb x Sr 1.9~2.1} Ca 1.9~2.1 Cu 3 O y (0 <x <0.4,10.0 <y <11.0), A method for producing a superconducting fibrous single crystal having a Bi ₂ Sr ₂ Ca ₂ Cu ₃ O ₁₀ structure (2223 phase).