CN1036099A - Oxide high-temperature superconducting material and preparation method thereof - Google Patents

Abstract

A high-temperature oxide superconducting material with a higher critical temperature, containing preferred orientation grains or non-altered grains, including LnR ₂ Cu ₃ O _X phase, in single crystal or polycrystalline form, wherein Ln is yttrium or a One (or more) rare earth metals, R is at least one selected from barium. The elements of calcium and strontium, X being 6.5 to 7, are obtained by synthesis in the presence of at least one element selected from alkali metals and bismuth.

Description

The present invention relates to an oxide high-temperature superconducting material, more precisely, relates to an oxide high-temperature superconducting powder, or a crystalline material with good orientation, and a kind of powder or crystalline material with high Superconducting wires of critical current density, and methods of making such materials and wires.

The application of superconducting materials is generally divided into two fields, the field of strong electric engineering suitable for large current and strong magnetic field, and the field of weak electric engineering suitable for small current or low voltage.

Most of the existing superconductors cannot be practically applied. It is known that materials that can be made into superconducting wires are intermetallic compounds such as _Nb3Sn , _Nb3Go , _Nb -Ti alloys and the like. The temperature at which superconductivity occurs in these alloys, known as the critical temperature Tc, is relatively low. The critical temperature of N _b3 Ge is the highest, which is 23K. N _b3 Go must be cooled with liquid helium.

Oxide superconducting materials with higher critical temperatures have recently been discovered, such as a La-Sr-Cu oxide (35-40K). and Y-Ba-Cu oxide (90-100K). The critical temperature of this Y-Ba-Cu oxide is much higher than the liquid nitrogen temperature (77K). Therefore, cooling Y-Ba-Cu oxides does not require the expensive liquid helium used to cool existing intermetallic compounds. That is, the Y-BaCu oxide can exhibit superconductivity by using cheap liquid nitrogen. Therefore, this Y-Ba-Cu oxide is regarded as a practical superconducting material and is required to be put into practical use.

Dr. J.G.Bodnorz and Dr. K.A.Mullor discovered a high-temperature superconducting material with a superconducting transition temperature much higher than that of existing superconducting materials in early 1986, that is, a lanthanum-barium-copper oxide (see Z.Pnys.BConderced Matter64 , 1986, PP.189-193), then, Dr. Zhu of the University of Houston in the United States discovered a yttrium-barium-copper oxide (referred to as Y-Ba-Cu oxide) in the spring of 1987 (see Physical Review Letters, Vol. 58, No.9, 1987, PP.908-910), and this Y-Ba-Cu oxide was also found in Japan (see Japanese, Journal of Applied Physics, Vol, 26 No.4, 1987, PP. L314-L315) are now in basic science concerning composition, crystal structure, properties and theory of superconducting materials, in the synthesis of superconducting materials and their applications in the fields of strong and weak electricity engineering, and in exploring more Much research and progress has been made on materials that are superconducting at high temperatures, such as room temperature.

Among the technologies to be researched and developed, the technology of making wires from superconducting materials is important as a basic technology in high-voltage engineering applications such as superconducting magnets.

In one of the most general methods of using Y-Ba-Cu oxides to make wires or strips, a metal sleeve is filled with Y-Ba-Cu oxide powder and processed into wires by swaging or wire drawing machines, Or processed into strip by rolling mill. The wire or strip is fired at about 900°C for several hours to sinter the Y-Ba-Cu oxide powder, so that the particles diffuse each other to form a superconducting path, otherwise there is no superconducting path.

The superconductor thus obtained has a perovskite-type layered crystal structure. The structure of the Y-Ba-Cu oxide superconductor is schematically shown in FIG. 2 . In Fig. 2, 1 represents yttrium, 2 represents Ba, 3 represents copper, 4 represents oxygen, and 5 represents oxygen (vacancy). The current flows on the crystal layer, that is, the current can easily flow on the axis plane of the axis b of the crystal (see Journal of the Japan Metal Society, Vol, 26, No, 10, 1987, P, 971). It is therefore important to orient the axis plane of the crystal axis -b in the longitudinal direction of the wire.

From the viewpoint of orientation, the melting-quenching method (see Symposium of Superconducting Substance Chemistry, Oct, 1987), and the compound vapor deposition method (see Japanese Patent Application No, 57-118002) have been studied. For example, superconducting thin films with excellent orientation have been obtained by chemical vapor deposition. This superconducting thin film has a high critical current density Jc, 10 ³ A/cm ² . However, this method cannot form long films or strands.

Metal superconducting materials are relatively easy to draw into wires, but oxide superconducting materials have poor ductility and are difficult to form wires. Therefore, to make a wire from an oxide superconductor, it is necessary to fill a metal tube with powder of the oxide superconductor, draw the tube, and heat-treat the drawn tube to sinter the oxide superconductor material. However, as described above, such an oxide superconducting material having a perovskite-type crystal structure is anisotropic in the direction of electric current. Moreover, because this material has a layered structure and the grains are in the form of sheets, it is difficult to plant them along the thin film of iliac rocks. improve. In addition, crystal orientation was not considered in the prior art. Therefore, the Y-Ba-Cu oxide crystals grow randomly and have no preferred orientation, so the obtained critical current density is low.

The critical current density at liquid nitrogen temperature (77K) of Y-Ba-Cu oxide prepared by the known method is about 2000 A/ ^cm² , as reported in Nikkan Kngyo Shimbun, October 7, 1987.

Generally, this oxide superconducting material can be obtained by mixing Y ₂ O ₃ (yttrium oxide), BaCO ₃ (barium carbonate) and CuO (copper oxide) so that Y:Ba:Cu is 1:2:3, at 900 These powders are calcined at around 950 °C, the calcined powder is ground and pressed, and the compacts are fired at around 950 °C for several hours. The critical temperature of the superconducting material obtained in this way can reach 90K, its grain size is several microns, and it includes a large number of <110> twins. This is because this material undergoes a phase transition between a high-temperature phase of a tetragonal structure and a low-temperature phase of an orthorhombic structure at around 650°C. Therefore, when the material changes from the high temperature region to the temperature region of this phase transition, twin crystals will be introduced to compensate for the volume change between the two lattice structures.

Such superconducting materials are being put into use as wire rods, but have the following problems.

(1). The critical current density Jc, that is, the upper critical current density required to maintain the superconducting state is lower, and (2). The critical magnetic field Hc, that is, the upper critical magnetic field temperature required to eliminate the superconducting state is lower.

The main reason for the low Jc is that there is a region with lower superconductivity (Tc) than that of the bulk of the grain in the non-uniform region such as the grain boundary. The reason for the low Hc is that the crystal anisotropy of Hc is high, and when a magnetic field is applied along the axial plane (plane) perpendicular to the axis b, Hc is one-fifth (1/5) of that when a magnetic field is applied parallel to the plane . The Hc of the whole polycrystal in which the grains are randomly arranged depends only on the Hc of the grains whose C-plane is oriented parallel to the applied magnetic field. Therefore, one solution to these concerns about Jc and Hc is to grow crystals along the axis plane (C plane) of the axis b, and another solution is to form a single crystal.

So far, one method of preparing single crystals of this superconducting material is a fusion method using CuO as a flux, see Japanese Journal of Applied Physics, Vol. 26, 1987, P.L1645. In this method, CuO and Ln Ba ₂ Cu ₃ Ox, (wherein Ln is Y or -rare earth element) are mixed according to the CuO:LnBa ₂ Cu ₃ Ox mole ratio of about 1:3, then heated to 1200 ° C, and then 5 °C/hr, and finally a single crystal with a size of about 1 square millimeter is obtained. Using CuO as a flux (if necessary, BaO can be added), the size of the single crystal obtained is about 1 mm ² and contains a large number of <110> twins.

In this fusion method, single crystals are grown in a CuO flux, making it difficult to remove from the flux. In addition, this melting method has the disadvantage that it cannot be used in general methods, namely, the Bridgeman method or the suspension zone melting method (FZ method), because these methods use stoichiometric raw materials.

Generally, when an oxide superconducting material having a stoichiometric ratio of LnBa ₂ Cu ₃ Ox is heated to 1200°C to melt, it decomposes into a liquid phase and a solid phase L Ln ₂ Ba ₁ Cu ₁ Ox. Even if the melt is cooled at a rate of 5°C/hr, only a small amount of the superconducting phase (denoted as (123) structure) with an oxygen-deficient three-layer perovskite structure in which the composition of LnBa ₂ Cu ₃ O _x is located can be obtained. Crystals, the majority of the crystals formed are insulating phases (denoted as (211), structure), also known as non-co-component materials. In this way, only about 10% of the superconducting phase can be obtained in the entire crystal phase. In addition, the resulting grain size is also very small, only about 50um at maximum.

_So just melting, cooling the raw material with the chemical _composition of _{LnB2Cu3Ox gives} only _small crystals and no _{crystals of LnBa2Cu3Ox} can be formed.

In the above-mentioned prior art, CuO is used as a flux to grow crystals, but the crystal size is only 1mm, and it also includes numerous twins with a pitch of 0.2um, so no real single crystal can be obtained. In addition, the Bridgeman method and the FZ method are not suitable, because they only get a small amount of superconducting phase.

The first object of the present invention is to provide a high-temperature oxide superconducting crystal with improved orientation and thus a higher critical current density Jc.

The second object of the present invention is to provide a powder raw material of a high temperature oxide superconducting material.

A third object of the present invention is to provide a superconducting oxide single crystal free of <110> twins.

A fourth object of the present invention is to provide methods for preparing the above-mentioned articles, powder raw materials and single crystals.

The fifth purpose of the present invention is to improve quality hook, quality hook, good grouper, and animal husbandry system.

Figs. 1(a) and 1(b) are electron micrographs showing particle shapes of an article made of a high temperature oxide superconducting powder material according to an embodiment of the present invention and a comparative example thereof.

Figure 2 is a schematic diagram of the oxygen-deficient three-layer perovskite structure of YBa ₂ Cu ₃ O _y .

Figures 3(a) and 3(b) are X-ray diffraction patterns of a product made of oxide superconducting powder material in one embodiment of the present invention and its comparative example, respectively.

4(a) and 4(b) are X-ray diffraction patterns of the oxide superconducting powder material in another example of the present invention and its comparative example.

Figures 5(a) and 5(b) are electron micrographs showing particle shapes of a product made of a high temperature oxide superconducting powder material in another example of the present invention and a comparative example, respectively.

6 and 8 are electron micrographs showing particle shapes in oxide superconducting materials in Example 1 and Example 3 according to the present invention, respectively.

7 and 9 are X-ray diffraction patterns of the oxide superconducting materials in FIGS. 6 and 8, respectively.

10(a), 10(b) and 10(c) are electron micrographs showing particle shapes in shaped articles made of oxide superconducting materials according to Example 7 of the present invention.

FIG. 11 is a graph showing the relationship between the heating temperature and the (002)/(200) diffraction intensity ratio in the X-ray diffraction diagram.

Figure 12 is a front view of a device used in one embodiment of the invention.

FIG. 13 is a schematic diagram illustrating the cross-sectional structure of Sample A in Example 9. FIG.

Fig. 14 is a schematic diagram illustrating a cross-sectional structure of Sample B in Example 6 as a comparison.

Figures 15 and 16 are X-ray images of samples obtained by the fusion method according to the present invention.

In order to achieve the above purpose, the present inventors considered that the oxide superconducting powder material filled in the metal sleeve should have good orientation along the longitudinal direction of the wire or strip when it is drawn or rolled into wire or strip. They have found through research that preferred orientation of crystals is easily achieved by heat treatment in the presence of at least one element selected from the group consisting of alkali metals and bismuth.

In the present invention, the desired high critical current density cannot be obtained only by improving the orientation of the crystals in the oxide superconducting material, but also by solidification with L _n Ba ₂ Cu ₃ O _x (where L _n is Y or a rare earth Elements) The melt of the oxide superconducting material with a stoichiometric ratio is obtained by a single crystal method, where the melt contains at least one element selected from the group consisting of alkali metals and bismuth.

Also, in another embodiment, the objects of the present invention are achieved by passing the oxide superconducting material through a region comprising a high temperature region and a low temperature region, in a direction from the high temperature region to the low temperature region.

According to the present invention, a high-temperature oxide superconducting material with L _n Ba ₂ Cu ₃ O _x composition, wherein L _n is yttrium or a rare earth element, and x is 6.5 to 7, such as YBa ₂ Cu ₃ O _7-δ in the presence of At least one element selected from alkali metals and bismuth is synthesized to promote grain growth. To mix alkali metal or bismuth with high-temperature mixed superconducting materials, an effective method is to use alkali metal or bismuth salt and keep the temperature above its melting point.

That is, for example, potassium, potassium carbonate has a melting point of 891°C. Effective grain growth can be obtained when the raw material of Y-Ba-Cu oxide superconducting material is synthesized in potassium carbonate above 891°C. There are two methods in the actual process, in the first one, the raw material of the oxide superconducting material undergoes solid-phase diffusion at a temperature lower than the melting point of the raw material in the presence of alkali metals and/or bismuth, in the second In , the raw material is first completely melted and then solidified or followed by heat treatment to grow crystals under the influence of alkali metals and/or bismuth. The role of alkali metals and bismuth is the same in both methods. That is, in both methods, crystal growth is significantly promoted. Because solid phase diffusion takes longer, the resulting material tends to contain less alkali metal than in the fusion process.

The above-mentioned first method will be explained below with an example of a potassium-containing YBa ₂ Cu ₃ O _7-δ material having an oxygen-deficient three-layer perovskite structure. The addition of potassium to the raw material or oxide Y·Ba ₂ Cu ₃ O _7-δ is done by powder mixing method, impregnation method or eutectoid method. Potassium is added in the form of compounds such as potassium nitrate or potassium carbonate. Then, the potassium-containing ┍ bosom is still in danger, but it is still in danger?

Powder raw materials (Y ₂ O ₃ for Y, BaCO ₃ for Ba, CuO for Cu, K ₂ CO ₃ for K) were processed as described above for the preparation of compacts. The blank was observed with an electron microscope (SEM). Figure 1(a) shows the observations. As a comparison, Fig. 1(b) shows the observation results for the K-free raw material body. It can be seen that the potassium-containing feedstock contains better-grown crystals than the potassium-free feedstock. The X-ray diffraction patterns of the surfaces of these formed blanks are shown in Fig. 3(a) and Fig. 3(b), respectively. The X-ray diffraction pattern of the potassium-containing billet in the (oon) plane is stronger. Potassium content is a few percent of the original comprehensive ingredients. This shows that the existence of potassium makes the flaky grains of YB ₂ Cu ₃ O _7-δ grow along a crystal direction (a-axis b-axis plane) where the current is easy to flow, while potassium itself disappears.

When it is split by mechanical grinding, the billet becomes small flakes, as shown in Figure 4(a), the enhanced X-ray diffraction pattern on the (oon) plane, and the SEM electron display shown in Figure 5(a) micro photo. As a control, the X-ray diffraction patterns and SEM photographs of the blanks without potassium are given in Fig. 4(b) and Fig. 5(b), respectively. As can be seen in Figures 4(b) and 5(b), the K-free billet contains smaller platelet grains that are aggregated together. The above-mentioned grinding can be accomplished by various methods, for example, a grinder (mortar and mill) or a ball mill. The degree of grinding is preferably such that the diffraction of the (oon) plane of the X-ray diffraction pattern is enhanced.

When making superconducting material, e.g., wire or tape, from the powdered material thus obtained, a metal tube is used which is filled with the powdered material, (i.e., containing a) grown crystals and b) potassium superconducting powder), the tube is drawn and/or rolled into wire or strip. Alternatively, the powder material is applied to a strip-shaped film on a substrate, and by applying a force to the film in a rolling direction in a direction perpendicular to the film, the sheet-like grains of the material are aligned longitudinally parallel to the strip-shaped film, thereby Increase the critical current density of the membrane.

The above explanation refers to potassium, but the same applies to lithium, sodium, rubidium, cesium and bismuth. The heat treatment temperature may be not lower than the temperature for decomposing the compounds of the above elements, but lower than the temperature for decomposing the oxygen-deficient layered perovskite structure, that is, in the temperature range of 400 to 1000°C, preferably in the range of 850 to 1000°C.

The above method has the following advantages:

(1). The presence of at least one element selected from the group consisting of alkali metals and bismuth contributes to the axial plane of the tabular grains in oxide superconductors such as YBa ₂ Cu ₃ O _7-δ , LaSrCuO or BiSrCa BiSrCaCu ₂ O along an axis b grow.

(2). The mechanical grinding of the superconducting material makes the flaky particles split on the (oon) plane well aligned along the preset direction; and

(3) A superconductor with good orientation and high critical current density can be obtained.

As described above, according to the present invention, the oxide superconducting material containing crystals grown in the direction in which current easily flows, and the oxide superconducting material can be made into tabular particles which can be easily aligned in a predetermined direction by grinding. Therefore, an oxide superconductor having a high critical current density can be obtained from the oxide superconducting material. For this superconducting material, existing wire or strip technology can be used.

On the other hand, the present inventors found that the orientation of the axial plane of one axis b of the crystal of a high temperature oxide superconductor can be set in the longitudinal direction of the superconducting article by heating the material under certain conditions.

In this method, an oxide superconductor _LnBa2Cu3Ox is heated through a _region containing a high-temperature zone and _a low-temperature zone, and the direction of material _travel is from the low temperature zone to the high temperature zone.

The high temperature is within the range of 850°C to the melting point of the oxide superconductor, and the low temperature is within the range of no more than 150°C. The distance from the highest temperature in the high temperature zone to the lowest temperature in the low temperature zone shall not exceed 80 mm. It is heat treated while passing through this zone at a rate of 0.2mm/hr to 50mm/hr.

After heat treatment, the material is preferably heated and annealed at 950° or lower in an oxygen atmosphere. Thereby further improving superconducting properties, such as critical temperature Tc and critical current density Jc.

The oxide superconducting material L _n Ba ₂ Cu ₃ O _x can be used alone or together with the metal casing. Best used with metal sleeves where the material is required to be in the form of wire.

When the grains are heated, diffusion initially occurs between the particles in contact, causing the particles to stick together at their contact surfaces. Then, the crystals start to grow while the diffusion continues. In the prior art, the entire mass of particles is heated to the same temperature. Therefore, the diffusion occurs in the whole particle, thus, the grain growth in the heated particle changes with the heating temperature and time. In this case, each grain grows unrestrictedly in any direction, so that the orientation of adjacent grains is completely random.

According to the present invention, the oxide superconducting material passes through a region containing a high temperature zone and a low temperature zone at a low speed; the distance between the two zones is relatively short and the temperature gradient is large, and the direction of travel of the material is from the low temperature zone to the high temperature zone. While the particles are calcined in the high temperature zone, the grains continue to grow in the direction of travel. As a result, grain orientation is preferred.

The temperature of the high-temperature zone and the low-temperature zone, the traveling speed and the distance between the two zones all have an effect on the crystal growth. In the high temperature zone, the particles interdiffuse, requiring higher temperatures to facilitate diffusion. Its temperature ranges from 850°C to the melting point of the superconducting material. In the low temperature zone, the diffusion rate is required to be very low. The maximum temperature is 150°C, the lower the better. Travel speed is an important factor to ensure the heating process and crystal growth. If the velocity is too large, there will be no continuous crystal growth. Therefore, the maximum speed cannot exceed 50mm/hr, but the minimum speed should not be lower than 0.2mm/hr. If the speed is lower than 0.2mm/hr, it will cause saturation. The distance between the two belts should not exceed 80mm to ensure continuous crystal growth.

Depending on the cooling rate, the resulting crystals can be tetragonal. In this case, to make it rhombic, the crystal needs to be heat-treated in oxygen at 950°C or lower to absorb enough oxygen into the crystal to make it superconductive.

In another approach to improving superconductivity, the inventors made single crystals that were planarly grown along the -axis and the b-axis.

In order to improve the superconducting properties, _part of Ba in _the stoichiometric _LnBa2Cu3Ox can be effectively replaced by 0.01 to 1 mole _of alkali metal or bismuth.

Incorporating 0.01 to 10 moles of an alkali metal salt AB (A represents an alkali metal, and AB represents a salt) into 1 mole of an oxide superconducting raw material with an idealized monoproportional ratio L _n Ba ₂ Cu ₃ O _x also Can improve superconducting properties.

0.01 to 10 moles of a mixture of CuO and BaCO ₃ can be added to 1 mole of the oxide superconducting raw material in which part of Ba is replaced by 0.01 to 1 mole of alkali metal, with an ideal stoichiometric ratio of L _n Ba ₂ Cu ₃ O _x , CuO/ The BaCO ₃ molar ratio is 5/95 to 100/0.

In addition, 0.01 to 10 moles of CuO, BaCO ₃ and a mixture of alkali metal salts AB can be added to 1 mole of oxide superconducting raw materials with an idealized monoproportion ratio L _n Ba ₂ Cu ₃ O _x , where CuO/BaCO ₃ The molar ratio is in the range of 5/95 to 100/0. The (CuO+BaCO ₃ )/AB molar ratio ranges from 99.99/0.01 to 50/50.

According to the method of the present invention, as prepared above, the oxide _{superconducting} raw material with an idealized single-proportion ratio _LnBa2Cu3Ox , ( _{wherein Ln} is at _least one selected from Y and rare earth metals and at least one added to the Elements selected from alkali metals and bismuth in the raw material) are heated into a molten body and then solidified.

The melt is effectively solidified in one direction.

When the melt is solidified, it can be made into a wire or a film. The film is formed on the substrate by immersing a substrate having a melting point higher than the temperature of the melt and having low reactivity with the melt into the melt.

The above-mentioned alkali metal or bismuth-containing oxide superconducting material is heated to a temperature in the range of 1050 to 1500°C to form a melt, which is effectively cooled at a rate of 1 to 300°C/hr.

The composition of the melt is, for example, L _n Ba _2-x A _x Cu ₃ O _x , where A is an alkali metal, and part of the added alkali metal replaces Ba in the (123) structure to stabilize the superconducting The formation of orthorhombic single crystals, and promote crystal growth. Solidification further promotes crystal growth.

Part of Ba in the idealized single ratio L _n Ba ₂ Cu ₃ O _x is preferably replaced by 0.01 to 1 mole of alkali metal. If the amount of substituting alkali metal is less than 0.01 mole, the superconducting (123) structure phase accounts for only a small part, while the (211) insulating structure phase accounts for the majority. If the amount of the alkali metal exceeds 1 mole, the critical temperature (onset Tc) is significantly lowered, and the obtained crystal is not a single crystal, and the alkali metal is precipitated alone or in the form of a compound.

0.01 to 10 moles of alkali metal salts can be added to 1 mole of the oxide superconducting material with an idealized monoproportional ratio of L _n Ba ₂ Cu ₃ O _x . If the amount added is less than 0.01 moles, no suitable material can be obtained, that is In other words, no superconducting single crystals are formed. If the amount added is more than 10 moles, the proportion of (123) structure in the melt is too small to obtain large-sized single crystals, and the diffusion length allowing the superconducting material to pass through the melt is too long to obtain large single crystals .

In order to obtain an oxide _{superconducting} raw material with _an idealized monoproportional ratio _LnBa2Cu3Ox , in which part of Ba is replaced by 0.01 _to 1 mole of alkali metal, 0.01 to 10 The mole can be a mixture of CuO and BaCO ₃ , the CuO/BaCO ₃ molar ratio is in the range of 5/95 to 100/0. If this molar ratio is out of this range. The L _n Ba ₂ Cu ₃ O _x component in which part of Ba is replaced by 0.01 to 10 moles of alkali metal is difficult to form.

A combination of 0.01 to 10 moles of CuO and BaCO ₃ , and a mixture of alkali metal salts AB can be added to 1 mole of the oxide superconducting material with an idealized monoproportion ratio L _n Ba ₂ Cu ₃ O _x , where CuO/BaCO ₃ The molar ratio is in the range of 5/95 to 100/0 (CuO+BaCO ₃ )/AB mixing ratio is 99.99/0.01 to 50/50. If the mixing ratio exceeds this range, it is difficult to replace Ba in the ideal stoichiometric ratio L _n Ba ₂ Cu ₃ O _x with alkali metal, and superconducting single crystal cannot be obtained.

In the _method according to the present invention, an oxide superconducting raw material having an ideal stoichiometric composition of _LnBa2Cu3Ox and containing at _{least one} element selected from alkali metals is heated and melted to form a melt. This melt _consists of _{a LnBaxCu3Ox} component in which part of Ba _is replaced by alkali metal. When the melt is solidified, part of the added alkali metal replaces part of Ba in the (123) structure to stabilize the formation of superconducting single crystal and promote the growth of single crystal.

On the other hand, grains preferentially oriented in one direction can be formed by establishing a temperature gradient in one direction in the melt and cooling it in that direction.

The melt may be cooled in a wire to form a wire from the melt.

A thin film of oxide superconducting material can be formed by immersing a substrate whose melting point is higher than the temperature of the melt and has low reactivity with the melt into the melt.

The melting point temperature of the oxide superconducting material is required to be in the range of 1,050 to 1,500°C. If the temperature is lower than 1,050°C, only part of the raw material is melted, and the molten volume is insufficient to grow crystals. If the temperature exceeds 1,500°C, CuO and BaO are decomposed and gasified violently, causing the composition to deviate from the predetermined value. The melt cooling rate is preferably 1 to 300°C/hr. If the cooling rate exceeds 300°C/hr, the crystal size is very small, only tens of microns. If the cooling rate is lower than 1° C./hr, it takes too much time and is not suitable for industrial use.

The oxide superconducting material prepared by the above method according to the present invention is a large-sized single crystal without twins with high critical current density.

The alkali metals mentioned here refer to lithium, sodium, potassium, rubidium and cesium.

A feedstock of composition _YBa2Cu3Ox is heated to a temperature below 1,050°C, _at which _the feedstock is not completely melted, where it does not contain alkali metals, and then cooled. The material thus obtained was analyzed by X-ray diffraction method. The results are given in Figure 16. It can be seen from Figure 16 that the material contains a large amount of (211) structural insulating phase Y ₂ BaCuO ₅ and a small amount of (123) structural superconducting phase. On the other hand, the raw material _{YBa1.8Na0.2Cu3Ox} was heated to 1,170°C where the raw material _was completely melted, and then _cooled at a rate of 6°C/ _hr . The resulting material was analyzed by X-ray diffraction method. The results are given in Figure 15. The X-ray diffraction pattern in FIG. 15 is completely different from that in FIG. 16 . That is, the X-ray diffraction pattern in Fig. 15 shows that the material includes only one superconducting phase, YBa ₂ Cu ₃ O _x (low temperature orthorhombic phase), and suitable materials can be obtained from alkali metal-containing raw materials. In addition, the obtained material was single crystal without any twinning. This is believed to be due to the fact that alkali metals stabilize the presence of the low-temperature orthorhombic phase even at temperatures close to the melting point.

The sources of alkali metals used herein are preferably oxides, chlorides, fluorides, nitrates, carbonates and the like.

The oxide superconducting materials prepared according to the present invention can have various applications. For example, a large-size single crystal can be formed on a thin sheet, and a high-density heat flow can be applied to the thin sheet to remove part of the thin sheet, thereby forming a linear pattern on the thin sheet.

In addition, single crystals according to the invention can be placed in a magnetic field, causing a transition from superconducting to normal, resulting in switching action of high currents.

The present invention will be described below with reference to examples and comparative examples.

But the present invention is not limited to these examples.

example 1.

Dissolve 16.5 grams of yttrium nitrate and 26.1 grams of barium nitrate in 2 liters of filtered water. To this solution, add a solution obtained by dissolving 100 g of ammonium carbonate in 1 liter of water with a micropump at a rate of 1 liter/hour, stirring properly while adding. Solid-liquid separation of the obtained precipitate was made in a grinder - a solution containing 1.02 g of potassium nitrate and 36.3 g of copper nitrate in 00 ml. The mixture was heated with stirring for about 1 hour. Concentrated, the stirred solid was recovered and dried at 130°C. Then, decompose part of the nitrate at 350 to 400°C, press the mixture into a size of 30mm in diameter and 3mm in thickness, pre-fire at 900°C for 3 hours, and then grind it. This process was repeated twice to obtain a black powder, hereinafter referred to as powder A. Press powder A with a pressure of 10 tons to make a briquette with a diameter of 30 mm and a thickness of 3 mm. The compact was then sintered at 920°C for 5 hours in oxygen. These briquettes (hereinafter referred to as briquette A) were ground by an agate mortar to obtain a powder, hereinafter referred to as powder A'. The SEM observation results of compact A are shown in FIG. 6 . SEM observation shows that there are 30 μm or longer long-shaped particles formed in the longitudinal direction. The results of X-ray diffraction analysis of powder A' are shown in Fig. 7. It can be seen that the peak of the (oon) plane is enhanced; indicating that the crystal has a preferred orientation. Chemical analysis indicated that the potassium content in powder A' was below quantifiable levels. This indicates that potassium promotes the crystalline growth of the particles.

Example 2.

5.7 grams of yttrium oxide, 11.9 grams of copper oxide, 1.1 grams of potassium oxide and 19.7 grams of barium carbonate were thoroughly mixed in an agate mixer (mortar and pestle), compacted in the same manner as in Example 1, and heated at 900 ° C for 3 hours , then grind. This process was repeated twice to obtain powder B. Powder B was pressed in the same manner as in Example 1, and heated at 950° C. for 5 hours in oxygen to obtain compacts B. These compacts were ground in the manner shown in FIG. 1 to obtain powder B'. The results of SEM observation of compact B and X-ray diffraction analysis of powder B' are given in Figs. 1(a) and 4(a), respectively. It can be seen from these figures that crystals are formed, and the X-ray diffraction peaks of the (oon) plane are enhanced.

Example 3

The potassium-free powder raw material was heat-treated at 900°C for 3 hours. Repeat this process two more times. The same procedure as in Example 1 was carried out to obtain powder C. Then, use 10 tons of pressure to press the powder into a size of 30mm in diameter and 3mm in thickness. These briquettes were placed under vacuum in a solution of 1 g of sodium nitrate dissolved in 10 ml of water for 1 minute so that the briquettes were saturated with the solution. After drying, these compacts were fired in oxygen at 920° C. for 5 hours to obtain a sintered compact C. These briquettes were ground in the same manner as in Example 1 to obtain powder C'. The results of SEM observation and X-ray diffraction analysis are given in Figs. 8 and 9, and it can be seen that there is crystal growth and (oon) planes are invented.

Example 4.

The potassium-free powder material was heat-treated in the manner of Example 3 to obtain powder D, and then 1.1 g of potassium nitrate was added to the mixture. Part of the mixture was pressed into a compact with a diameter of 30 mm and a thickness of 3 mm with a pressure of 10 tons. The compact was fired in oxygen at 920° C. for 10 hours to obtain a sintered compact D. These briquettes were ground as in Example 3 to obtain powder D'. The results of SEM observation and X-ray diffraction analysis indicated that crystals were formed and (oon) faces developed.

Comparative example 1

A potassium-free feedstock was treated in the manner of Example 1 to obtain briquette E and powder E'. In addition, another kind of potassium-free raw material is also processed in the manner of Example 1 to obtain compact F and powder F'. The results of SEM analysis on compact F are given in Fig. 1(6). Visible crystal growth is less. The results of the X-ray diffraction analysis of the powder F are shown in Fig. 4(a), and it can be seen that there are no (oon) plane peaks. In addition, the same SEM observation results and X-ray diffraction patterns were obtained for the compact E and the powder E'.

Example 5

The same process as in Example 2 was carried out, except that the potassium-free raw material was fired at 900° C. for 3 hours, and pressed in powder form to obtain Powder B. Then, a part of the powder was pressed into a briquette with a diameter of 30 mm and a thickness of 3 mm with a pressure of 10 tons. The briquettes were immersed in a solution obtained by dissolving 2 g of potassium carbonate in 10 ml of water for 1 hour to fully soak the briquettes. After drying, these compacts were fired in oxygen at 950° C. for 10 hours to obtain sintered compact G. SEM observation and X-ray diffraction analysis of powder E' in the same manner as in Example 2 showed that crystals were grown on the (oon) plane.

Example 6

Powder B was obtained in the manner of Example 5. Add 1.1 g of potassium carbonate to Powder B and mix well. The powder was then pressed into compacts with a diameter of 30 mm and a thickness of 3 mm. These compacts were fired in oxygen at 950°C for 10 hours to obtain a sintered compact H. SEM observation and X-ray diffraction analysis of powder H' in the same manner as in Example 2 showed that crystals had grown on the (oon) plane.

Example 7

The procedure of Example 2 was repeated except that lithium, rubidium, and cesium carbonates were used instead of potassium carbonate to obtain sintered compacts I, J, and K, respectively. The SEM micrographs of these compacts I, J and K are given in Fig. 10(a), 10(b) and 10(c), respectively. It can be seen that the crystal growth conditions are better than those in Comparative Example 1.

Example 8

The briquette A, briquette B, briquette C, briquette D, briquette E, briquette F, briquette G, and briquette H were all cut into a size of 2 mm x 20 mm x 1 mm. The initial critical temperature and the critical current density at 77K are determined by the usual four-junction resistance method. The results are shown in Table 1

Table 1

Sample Tc (starting) Jc (at 77K)

Briquettes A 94K 1, 610A/cm ²

Briquette B 93K 1,400A/cm ²

Briquette C 94K 1,750A/cm ²

Briquette D 94K 1, 680A/cm ²

Briquette E 93K 330A/cm ²

Briquette F 94K 430A/cm ²

Briquette G 94K 1,700A/cm ²

Briquettes H 94K 1, 690A/cm ²

Example 9

A silver tube with an inner diameter of 6 mm was filled with powder A' and drawn into a wire with a diameter of 1.2 mm. The drawn wire rod was cold rolled to form a strip wire having a thickness of 0.2 mm. The tape was burned in oxygen at 925°F for 20 hours, and then slowly cooled to room temperature to obtain a superconducting wire. The critical current density was measured at 77K, O Tesla magnetic field, and the Jc was 15,000A/cm ² .

Example 10

The procedure of Example 9 was repeated except that Powder C' and Powder D' were used. Wires were made from these powders and their Jc determined. For powder C', Jc was 14,500 A/cm ² , and for powder D', Jc was 17,500 A/cm ² .

Powder A', powder C' and powder D' were pressed into a compact having a diameter of 30 mm and a thickness of 3 mm. Each briquette was immersed in a 20 wt% potassium carbonate aqueous solution under vacuum. After it was dried, it was fired at 500° C. for 1 hour. These briquettes were then ground in a grinder (mortar and pestle) to obtain powder A", powder C" and powder D". Using powder A", powder C" and powder D" to make wires in the manner of Example 9, and to measure their Jc. The Jc of the wires using powder A", powder C" and powder D" were 30, 100 A/cm ² , 331,000 A/cm ² , and 29,800 A/cm ² , respectively.

Example 12.

Using the powder B' and the silver-palladium alloy tube as in Example 9, a ribbon-shaped wire was obtained. The wire was then fired at 950°C for 20 hours in oxygen and cooled to room temperature. According to the method of Example 8, the Jc of the wire rod was determined to be 20,700A/cm ² .

Example 13.

Repeat the process of Example 12, except that powder G' and powder H' are used to prepare wires and measure their Jc. For powder G', Jc was 21,500 A/cm ² , and for powder H', Jc was 19,900 A/cm ² .

Example 14.

With powder B ', powder G ' and powder H ', obtain powder B ", powder G " and powder H " in the manner of example 11 ". Use these powders to make strip-shaped wire rod and determine its Jc. To powder G ", Jc is 32,000A/cm ² , for powder H″, Jc is 31,000A/cm ²

Example 15.

In the manner of Example 12, use the powder B″, powder G″ and powder H″ of Example 14 to make ribbon-shaped wires and determine their Jc. For powder B″, Jc is 35,000A/cm ² , and for powder G″, Jc is 34 , 500A/cm ² , for powder H″, Jc is 35,500A/cm ² .

Comparative example 2

In the same manner as in Example 9, powders E' and F' were used to produce superconducting wires and their Jc was determined. Jc was 2,600 A/cm ² for powder E' and 3,300 A/cm ² for powder F'.

Comparative example 3

In the same manner as in Example 9, the powder F' was used to make a wire, and its Jc was measured to be 3,600 A/cm ² .

Example 16

Sintered compacts were obtained in the same manner as in Example 1, except that the heating temperatures in oxygen were 800, 850, 900, 920, 950 and 1,000°C. These briquettes were ground up for X-ray diffraction analysis. Calculate the (002)/(200) intensity ratio of the X-ray diffraction pattern. In FIG. 11 , the peak of the (002) plane and the peak of the (200) plane do not cover the peaks of other planes. The higher the (002)/(200) ratio, the better the orientation of the crystal. The relationship between the (002)/(200) ratio and the sintering temperature is represented by curve (a) in Figure 11. It can be seen that when sintered at 850 to 1000 ° C, the c of the pastoral series sodium osprey agent, Hai Piao Lu, is 90 ° K or higher.

Comparative example 4.

The same experiment as in Example 16 was carried out with respect to the components of Comparative Example 1 (excluding potassium). The result is represented by curve (b) in Fig. 11 . It can be seen that when sintered at 850 to 950°C, the initial Tc of the material is 91K or higher.

Example 17.

5.7 g of yttrium oxide, 11.9 g of copper oxide, 19.7 g of barium carbonate and 5.5 g of bismuth oxide were mixed in a grinder (mortar and pestle) and pressed into a compact 30 mm in diameter and 3 mm thick. These compacts were presintered at 900°C for 3 hours and ground. The resulting powder was compacted and fired at 930°C for 5 hours. These compacts were ground in the same manner as in Example 1, and they were subjected to SEM observation and X-ray diffraction analysis. It was found that crystals were formed, and the round shape of the (00n) plane was enhanced.

A sample of size 2 mm x 20 mm x 1 mm was cut from the billet. Using the conventional four-junction resistance method, the critical current density and critical temperature of the sample at 77K. The initial Tc is 94K, and the Jc is 1,580A/cm ² .

Example 18

5.7 g of yttrium oxide, 11.9 g of copper oxide, 19.7 g of barium carbonate, 2.7 g of bismuth oxide and 0.8 g of potassium carbonate were mixed and pressed as in Example 17, fired at 900°C for 3 hours and ground. The resulting powder was compacted as in Example 17 and fired at 930°C for 5 hours. The resulting compact was ground as in Example 17. SEM observation and X-ray diffraction analysis were performed on the obtained powder. It is found that there is crystal formation, and the pattern of (00n) plane is enhanced. Determine the superconducting properties according to Figure 17. The initial Tc is 93K, and at 77K, the Jc is 1.720A/cm ² .

Example 19

This example will be described with reference to Figs.

Fig. 12 shows a front cross-sectional view of an apparatus for preparing a high temperature oxide superconducting material with preferred orientation crystals. In this figure, 11 is a high temperature oxide superconducting material, 12 is a metal sleeve, 15 and 16 are the inlet and outlet of cooling water, and 17 is a thermal insulator. A is the highest temperature zone and B is the lowest temperature zone. The distance between A and B is about 80mm or less.

The high temperature oxide superconducting material 11 was prepared in the following manner. The raw material adjusted to YBa ₂ Cu ₃ O _7-δ composition by solid phase reaction was milled with a centrifugal ball mill for 24 hours to obtain a powder with an average particle size of 1.2 μm. This powder was filled into a silver tube with an outer diameter of 6 mm and a thickness of 0.5 mm so that the density of the filled powder was 2.7 g/cm3. Both ends of the tube were sealed, drawn into a wire with a diameter of 2.8 mm by a wire drawing machine, and rolled into a strip with a thickness of 0.05 mm by a rolling mill. Using the apparatus shown in Fig. 1, the ribbon was subjected to crystal orientation treatment under the following conditions. That is, the temperature in the high temperature zone is 920°C, and the temperature in the low temperature zone is 80°C. The sample travel speed was 10 mm/hr. The distance between the two temperature zones is 70mm. The sample thus obtained was fired in oxygen at 920°C for 20 hours and then cooled at a heating rate of 200°C/hr and a cooling rate of 200°C/hr. This sample is referred to as sample I hereinafter.

Comparative Example 5

On the other hand, a comparative sample was prepared by the known method. That is, the powder of Example 19 was used to form a tape having a thickness of 0.05 mm. The tape was heat-treated at 920°C for 20 hours in oxygen at a heating rate of 200°C/hr and a cooling rate of 200°C/hr without crystal orientation treatment. The sample thus obtained is referred to as Sample J.

13 and 14 are schematic diagrams showing the cross-sectional structures of samples I and J, respectively. It can be seen that the sample I made according to the present invention contains crystal grains oriented along the traveling direction of the sample, while the crystal orientation of sample J made by the prior art is disordered and random. In addition, the crystal grains in Sample I are larger than those in Sample J.

The fracture surfaces of samples I and J were observed by SEM. In the grains of sample I, lath-shaped deformation crystals were observed, which were generated when the tetragonal system transformed from the tetragonal system to the orthorhombic system after heat treatment at 920°C for 20 hours. However, in Sample I, the metamorphic crystals were generated in the same direction between adjacent grains. On the other hand, in Sample J, such lath-shaped crystals were not observed.

The critical current density was determined in liquid nitrogen by the common four-junction resistance method. The distance between voltage contacts is 10mm. When the voltage between the contacts reaches 1μv, measure the current value. The current value is divided by the surface area of the sample perpendicular to the current direction to obtain the critical current density. Determine the cross-sectional area with an optical microscope. Table 2 gives the critical current densities of samples I and J.

Table 2

Sample critical current density (A/cm ² )

I 8,300

J 2,500

It can be seen from Table 2 that the Jc of sample I is as high as 8,300A/cm ² , while samples J and J are 2,500A/cm, which is only one-third of the Jc of sample I.

Example 20

Yttrium oxide (Y ₂ O ₃ ) with a purity of 99.9%, barium carbonate (BaCO ₃ ) with a purity of 99.5%, copper oxide (CuO) and sodium carbonate (NaCO ₃ ) were used. As raw materials, these powders were weighed and mixed to have a _composition of _LnBa2Cu3Ox , where X _ranges from 0 to 1.2. These mixtures are designated as Sample Nos. 1 to 5, as shown in Table 3. Grind and mix with a grinder (mortar and pestle) for 30 minutes. Then, put the mixed powder into the crucible of an electric furnace, heat it in oxygen at a rate of 400 °C/hr to 1,200 °C and maintain this temperature for 10 hours, and then cool it to 900 °C at a rate of 6 °C/hr. °, and then cooled to room temperature at a cooling rate of 100°C/hr. Take out the crucible from the electric furnace, break the crucible with a hammer to get a single crystal, and observe the size of the single crystal and the existence of bent crystal by differential interference microscope. The crystal phase was determined by X-ray diffraction method. The superconducting properties were determined by the usual four-junction method. The results are shown in Table 3

table 3

Compound Measurement Results

Sample No. YBa _2-x Nax Average crystalline metamorphic crystal structure Superconductivity

Cu ₃ Oy size starting Tc

1 X＝0 5μm Yes 211+123 Undeterminable

2 X＝0.01 2.1mm None 123 96K

3 X＝0.1 2.4mm None 123 95K

4 X＝1.0 3.1mm None 123 92K

5 X＝1.2 1.0mm No 123+ impurity 78K

Note: Samples 1 and 5 are comparative examples.

Samples 2 to 4 belong to the present invention.

According to the present invention, it can be seen that when X is in the range of 0.01 to 1.0 mm, a large single crystal without any impurity and good superconductivity can be obtained.

On the other hand, Samples 1 and 5, which are outside the scope of the present invention, are inferior in crystal size, metamorphism and superconductivity. The above 123 structure represents a Y-Ba-Cu oxide superconducting material with a Y:Ba:Cu ratio of 1:2:3. The above "211 structure" indicates an oxide material exhibiting superconductivity in a Y:Ba:Cu ratio of 1:2:3.

The critical temperature Tc is the temperature at which the resistance is zero (0), and the onset Tc is the temperature at which the resistance becomes almost zero (0).

Example 21

Example 2. The same _raw material used in _Y2O3 with _a purity of 99.9%, _BaCO3 , CuO and _K2CO3 powders were weighed to make K( _CO3 ) 0.5 content compared with YB _a2 CuO in 0 to 12 moles , and then mix them. Samples 6 to 10 listed in Table 4 were obtained. Single crystals were prepared from these powders in the same manner as in Example 20. The single crystal size, presence or absence of variable crystals, and superconducting properties were determined. The results are listed in Table 4.

Table 4

Measurement results per "123"

Sample No. K(CO ₃ ) ₅ Average crystalline metamorphic crystal structure Superconducting onset Tc

Content Size

6 0mol 5μm Yes 211+123 -

7 0.01mol 2.4mm No 123+ impurity 95K

8 1mol 3.0mm None 123 94K

9 10mol 1.5mm None 123 92K

10 12mol 0.5mm No 123+ impurity -

Note: Samples 6 and 10 are comparative examples.

Samples 7 to 9 belong to the present invention.

It can be seen from Table 4 that a single crystal with good superconductivity can be obtained by incorporating 0.01 to 10 mol of K(CO ₃ ) _0.5 into YBa ₂ Cu ₃ Oy.

On the other hand, Samples 6 and 10 outside the range of the present invention had smaller grain sizes than Samples 7 to 9 and were inferior in superconductivity.

Example 22

Y ₂ O ₃ , Ba _{CO 3} , _Cu O and Na ₂ CO ₃ powders used in Example 20 were used as raw materials in this example. The CuO/B _a CO ₄ molar ratio is 5/95 to 100/0.

Samples 11 to 15 had CuO and Ba _{CO 3} contents of 0.01 to 12 moles per mole of YBa _1.8 Na _0.2 Cu ₃ Oy. Single crystals were prepared from these materials in the same manner as in Example 20. The size of the obtained single crystal, presence or absence of variable crystals and superconductivity were determined. The results are listed in Table 5

table 5

Sample No. Components Determination Results

A B Average Crystalline Variable Crystalline Crystal Structure Superconducting Onset

Size Tc

11 5/95 3 0.4mm No 123+ impurities -

12 10/90 3 2.1mm No 123+ impurities 96K

13 100/0 3 2.3mm No 123+ impurities 93K

14 50/50 0.01 2.2mm No 123+ impurities 94K

15 50/50 12 0.6mm No 123+ impurities -

Note: A is the CuO/BaCO _molar ratio.

B is the number of moles of C _u O and _Ba CO ₃ per mole of YBa _1.8 Na _0.2 Cu ₃ Oy.

Samples 11 and 15 are comparative examples.

Samples 12 to 14 belong to the present invention.

Samples 11 and 15, which are outside the scope of the present invention, have smaller crystal sizes and poorer superconductivity than samples 12 to 14.

Example 23

Y ₂ O ₃ , _Ba CO ₃ , CuO and KCO ₃ powders of Example 21 were used as raw materials. The CuO/BaCO ₃ molar ratio ranges from 5/95 to 100/0. K(CO ₃ ) _0.5 is incorporated into this mixture in such an amount that the (CuO+B _a CO ₃ )/K(CO ₃ ) _0.5 molar ratio is in the range of 99.99/0.01 to 50/50. Samples 16 to 20 were prepared by adding 3 to 12 moles of this mixture per YB _a2 C _u3 O _y to other powders. Single crystals are made from these materials. The crystal size, presence or absence and superconductivity of these samples were determined. The results are listed in Table 6.

Note: Samples 16 and 20 are comparative examples.

Samples 17 to 19 belong to the present invention.

Samples 16 and 20, which are outside the scope of the present invention, have smaller crystal sizes and poorer superconductivity than samples 17 to 19.

Example 24

The Y ₂ O ₃ , Ba _{CO 3} , _Cu O and Na _{CO 3} powders used in Example 20 were weighed and mixed as in Example 20 to obtain YB _a2 C _u3 Oy. The powder was put into an alumina crucible and fired in oxygen at 950°C for ₁₀ hours to obtain _Ba2Cu3Oy , which was then ground in a grinder (mortar and pestle). The obtained powder is pressed into a cylinder with a diameter of 5 mm and a height of 100 mm under a pressure of 1 ton/cm2 by isostatic pressing. The cylinder is placed on a sample holder moving at a constant speed in a single crystal preparation apparatus. The sample was heated with a central infrared heating system. So that the sample in the device is only melted in the peripheral part to form a single crystal. The growth conditions are as follows: the atmosphere is 5 atm of _O2 gas; the width of the melting zone is about 2 mm; the sample moving speed is 1 mm/hr; the melting point temperature is 1,200 °C. This gave a rod-shaped sample with a diameter of 3 mm and a length of 30 mm. X-ray diffraction analysis found that the sample was a single crystal. The onset Tc was determined to be 95K by the four-contact method.

The melt used in this example can also be solidified in the direction of a temperature gradient applied to the apparatus to obtain a material containing preferentially oriented grains.

Example 25

A powder containing "123 structure" crystals was obtained by the procedure of Example 24. The powder was compressed isostatically at a pressure of 1 ton/cm2 to form a 3 x 30 x 1 mm block. The gas used here is oxygen and a CO ₂ laser (power 150W, spot diameter 3mm) is scanned on the block at a speed of 1mm/min. The ambient gas used here is _O2 gas. The sample is in a molten state at the laser point. The obtained sample consisted of many 2 mm large grains, which were elongated in the laser moving direction. Current can flow through the sample along its longitudinal direction. The critical current density of this sample was measured at 77K by the four-junction method to be 10,000 A/cm ² .

In both the method of using the melt of ideal stoichiometry and the flux method, the substrate whose melting point temperature is higher than the temperature of the melt and which is not easy to react with the melt can be immersed in the melt and maintained therein for a predetermined period of time. , and then taken out from it, thereby easily obtaining a superconducting film.

Alternatively, superconducting fibers for wires can be produced by spraying a melt in a stoichiometric ratio through a nozzle. Of course, the grain size varies with the preparation conditions.

The single crystal prepared according to the invention is suitable for researching material properties and practical application of materials.

In the case of a stoichiometric melt, large-diameter single crystals can also be prepared by the Bridgeman method or the FZ method. Such a large-diameter single crystal can be subjected to, for example, ion implantation or laser beam irradiation treatment to break a part of the crystal to lose its superconductivity, thereby engraving an electronic circuit pattern on the crystal to form a circuit board.

Claims (30)

1. A method for preparing a high temperature oxide superconducting material comprising LnR ₂ Cu ₃ Ox phase with high critical current density, wherein Ln is yttrium or a rare earth metal (or several), and R is at least one selected from barium , elements of calcium and strontium, X is 6.5 to 7, the method comprises synthesizing said material in the presence of at least one element selected from alkali metals and bismuth to form grains containing preferentially oriented grains or grains without metamorphic grains the material. 2. A method according to claim 1, wherein said oxide superconducting material has an oxygen deficient layered perovskite type structure. 3. A process according to claim 1, wherein said alkali metal is used in the form of a salt. 4. A method according to claim 1, wherein said feedstock of oxide superconducting material is passed through a zone comprising a high temperature zone and a low temperature zone. The running direction is from low temperature to high temperature zone, so as to set the grain orientation in a predetermined direction. 5. A method according to claim 4, wherein the temperature range of said high temperature zone is 850°C to the melting point of said oxide superconducting material, the temperature range of said low temperature zone is below 150°C, said high temperature zone and The distance between the low temperature zones does not exceed 80mm. 6. A method according to claim 4, wherein said material is moved through said zone at a rate of 0.2 mm/hr to 50 mm/hr. 7. A method according to claim 4, wherein said oxide superconducting material is used alone or in combination with a metal sheath. 8. A method according to claim 1, wherein said oxide superconducting material is synthesized from a melt of a solidified raw material. 9. A high-temperature oxide _{superconducting} material with high critical current density, which comprises _LnR2Cu3OX phase, wherein _Ln is yttrium or one (or more) rare earth elements, and R is at least _{one selected} Elements selected from barium, calcium and strontium, X is 6.5 to 7, with or without at least one element selected from alkali metals and bismuth, and contains single crystals with preferred orientation or crystals without crystal transformation. 10. A high temperature oxide superconductor according to claim 9, wherein said oxide superconducting material is prepared by cooling a raw material melt. 11. A high temperature oxide superconductor according to claim 9, wherein part of Ba in the stoichiometric LnR ₂ Cu ₃ Ox is replaced by 0.01 to 1 mol of alkali metal. 12. A high temperature oxide superconductor according to claim 9, wherein 0.01 to 10 moles of an alkali metal, AB, where A represents an alkali metal is added to 1 mole of said raw material of LnB _a2 C _u3 Ox. 13. A high temperature oxide superconductor according to claim 9, wherein 0.01 to 10 moles of a combination of CuO and _BaCO3 are added to ₁ mole of said oxide superconducting material, wherein the molar ratio of CuO/BaCO3 is 5/95 to 100 /0 range, in the material, part of Ba of LnB _a2 C _u3 Ox is replaced by 0.01 to 1 mole of alkali metal. 14. A high-temperature oxide superconductor according to claim 9, wherein 0.01 to 10 moles of CuO/ _BaCO3 having a molar ratio ranging from 5/95 to 100/0 of CuO and A mixture of BaCO ₃ and an alkali metal salt AB, wherein the (CuO+BaCO ₃ )/AB molar ratio is in the range of 99.99/0.01 to 50/50. 15. A method of preparing a high temperature oxide superconducting material in single crystal form, which comprises melting LnB _a2 C _u3 Ox having a stoichiometric ratio (wherein Ln is yttrium) in the presence of at least one element selected from the group consisting of alkali metals and bismuth or rare earth elements) oxide superconducting material, and solidify the melt. 16. A method according to claim 15, wherein said melt solidifies in a predetermined direction. 17. A method according to claim 9, wherein said melt is solidified to form a superconducting wire. 18. A method according to claim 9, wherein said melt is solidified by immersing a substrate having a melting point higher than the temperature of the melt, which is not easily reacted with the melt, into the melt, thereby forming a substrate on the substrate.ぁ? 19. A method according to claim 9, wherein said raw material is melted at a temperature between 1,050 to 1,500°C to form said melt, said melt at 1 to 300°C/ The cooling rate of hr is cooled. 20. A circuit board comprising a thin sheet of oxide superconducting material in single crystal form produced by the method of claim 15 having a circuit pattern formed with a high density heat beam. 21. A high current switching element using said high temperature oxide superconductor in single crystal form produced by the method of claim 15. 22. A sheet-shaped high temperature oxide superconducting material prepared by the method of claim 1. 23. A high temperature oxide superconducting material according to claim 22, having a length of 30 m or more. 24. A method of preparing a wire from the high temperature oxide superconducting material produced by the method of claim 1, comprising grinding said material, filling a hollow conductor with said material powder, and drawing said conductor to form a wire , and roast the wire. 25. A method of preparing a ribbon wire from the high temperature oxide superconducting material produced by the method of claim 1, comprising grinding said raw material, filling a hollow conductor with powder of said raw material, drawing said wire forming wire, rolling the wire, forming a wire strip and firing the wire strip. 26. A method of preparing a wire from the high temperature oxide superconducting material produced by the method of claim 1, comprising grinding said material to form a powder, mixing the powder with at least one element selected from the group consisting of alkali metals and bismuth , fill a hollow conductor with the mixture, stretch the conductor to form a wire, and fire the wire. 27. A method of preparing a ribbon-like wire from a high temperature oxide superconducting material produced by the method of claim 1, which comprises studying said material to form a powder, mixing the powder with at least one element selected from the group consisting of alkali metals and bismuth mixing, filling a hollow conductor with the mixture, drawing the conductor into a wire, rolling the wire to form a ribbon wire, and firing the ribbon wire. 28. A method according to claim 24, wherein said firing is carried out at a temperature between 400 and 1,100°C. 29. A method according to claim 26, wherein said calcining is carried out at a temperature between 400 and 1,100. 30. A product made of a high temperature oxide superconducting material in the form of flake fine-grained powder, with the (00n) plane in its thickness direction.

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