JPH07172995A - Single crystal of superconducting oxide and method of using the same - Google Patents

Abstract

(57) [Summary] [Objective] To provide a single crystal of a superconducting oxide having a definite crystal orientation, and to provide a method for using the same. [Structure] La-Sr-Cu-O system, Nd-Ce-C
u-O type, Y-Ce-Cu-O type, Y-Ba-Cu-O
System or Bi-Ca-Ba-O system, etc., wherein the crystal is a tetragonal system and the crystal growth direction is the a-axis, a single crystal of a superconducting oxide, and the c-axis of the single crystal How to use the current flow in the direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a superconducting oxide having a critical temperature at a high temperature, particularly La _2−x A _x CuO ₄ (A: Sr,
_{Ba), Nd 2-x Ce} x CuO 4, YBa 2 Cu 3 O
_{7-x, BiSrCaCu 2 O x} , Tl 2 Ba 2 Ca 2
The present invention relates to a single crystal such as Cu ₃ O _x and a method of using the same.

[0002]

2. Description of the Related Art 1986, J. G. Bedonorz
And K. A. Since Dr. Muller discovered that even metal oxides exhibit superconductivity at high temperatures, many researches on superconducting oxides have been conducted around the world. Certain oxides such _{La 2-x A x CuO 4} (A: Sr, B
_{a), Nd 2- x Ce x} CuO 4, YBa 2 Cu 3 O
_{7-x, BiSrCaCu 2 O x} , Tl 2 Ba 2 Ca 2
It is known that Cu ₃ O _{x and the} like exhibit superconductivity at a critical temperature higher than that of conventional metal-based superconducting substances, although the density of states of electrons is extremely low.

Most of the research on these oxides mainly deals with sintered materials and thin films, and the researches on the relationship between the crystal structure, the chemical composition and the critical temperature have been carried out in quite detail. However, the established principle has not yet been found for the superconducting mechanism of these oxide superconducting materials. Most of the oxide superconducting substances reported to date have a perovskite lattice as a basic structure and, unlike metal or alloy superconducting substances, belong to tetragonal or orthorhombic rather than cubic. Therefore, information on the anisotropy cannot be obtained from the physical properties of the sintered material, which is a set of polycrystals, and it is difficult to obtain information in the thickness direction of the thin film, which makes it difficult to construct a mechanism for manifesting superconductivity. Be done.

To measure the anisotropy of the magnetic and electrical properties of oxides strictly and obtain information on the anisotropy to elucidate its superconductivity, a large single crystal of good quality is used. A body is required, and for this reason, it is desired to grow a large crystal of good quality. To date, single crystals of high-temperature oxide superconducting materials that have been reported to be grown are La-Sr-Cu-O-based, N-based.
d-Ce-Cu-O system, Y-Ba-Cu-O system and Bi
-Ca-Ba-O type and the like. Since most of these substances are considered to be decomposed and fused compounds, the pulling method and Bridgman method such as melting and solidification, which are used for general oxide single crystals, cannot be applied to grow single crystals. The method mainly used is the flux method and the top seed method devised from the flux method. Regarding the Bi-based single crystal, the floating zone method (flo) is used by Takekawa et al.
Attempting using the A.Z. Cryst. Growth, 92 (1988)
p. 687. In addition, as for La ₂ CuO ₄ and CuO having a eutectic composition, L. Troilleux, G .; Dhale
nn and A. Revcollevschi: Cr
yst. Growth, 91 (1988) p. 268.

In many cases, the solvent used in the flux method is called CuF self-flux, and after the crystal growth, the flux and the generated crystals are mechanically separated from each other. Separation of grown crystals is difficult.
However, in the example of lanthanum-based La _2−x A _x CuO ₄ ,
The crystals growing in the flux and sinking to the bottom of the crucible are scooped up and an attempt is made to separate them from the solvent. In any case, the size of the crystal grown by the flux method is not so large, and if it is large, the inclusion of flux is observed. In addition, a thin plate crystal is generally grown in the c-axis direction.

Table 1 shows the size of the grown crystal, the solvent used and the growing method, the critical temperature, etc., which have been reported so far for the lanthanum single crystal.

[0007]

[Table 1] It can be seen from Table 1 that most of the grown crystals are plate-shaped crystals as described above. The size of the crystal grown by the top seed method is relatively large, 25 × 25 × 5 mm, but the critical temperature is very low. Sr (B
It is considered that this is because a) is less than the raw material composition. Further, in the example by the floating zone method shown at the end of Table 1, although the crystal is large and the critical temperature is higher than the other methods, the raw material composition is a eutectic composition with CuO and the grown crystal is Is also a eutectic containing CuO and cannot be said to be a single-phase crystal.

[0008]

As described above, the crystal size of the conventional superconducting oxide is not so large, and if it is large, the inclusion of flux is observed. Further, since it is a thin plate crystal in the c-axis direction, by strictly measuring physical properties such as anisotropy of magnetic and electrical properties of the oxide,
There is a problem that it is difficult to obtain anisotropic information and it is difficult to contribute to the construction of the mechanism of superconductivity.

The present invention has been made in order to solve the above-mentioned problems, and it is a high quality single crystal having a definite crystal orientation that can be used to clarify the superconductivity of an oxide. It is an object of the present invention to obtain an oxide single crystal having a large crystal and to provide a method of using a current in the c-axis direction of the single crystal.

[0010]

A single crystal of a superconducting oxide according to the present invention is a La-Sr-Cu-O system, Nd-Ce-.
Cu-O system, Y-Ba-Cu-O system or Bi-Ca-B
It is characterized in that it is an a-O system crystal, the crystal is a tetragonal system, and the crystal growth direction is the a-axis.

The method of using the single crystal of the superconducting oxide according to the present invention is La-Sr-Cu-O system, Nd-Ce-.
Cu-O system, Y-Ba-Cu-O system or Bi-Ca-B
It is characterized in that a current is caused to flow in the c-axis direction of a single crystal of a tetragonal superconducting oxide among a-O type crystals.

[0012]

In the single crystal of the superconducting oxide of the present invention, the crystal is tetragonal and the growth direction of the crystal is L-axis.
a-Sr-Cu-O system, Nd-Ce-Cu-O system, Y-
It is a Ba-Cu-O-based or Bi-Ca-Ba-O-based crystal, and good superconducting properties can be obtained by passing a current in the c-axis direction of a single crystal of this superconducting oxide. And
This large single crystal is a solvent transfer floating zone method: Travel
Ling Solvent Floating Zone
It is grown in a large size by e Method (called TSFZ method). This TSFZ method is described in G.
A. Wolff: “CRYSTAL GROWTH T
theory and Technologies pp19
4-230 "GHL Goodman Ed, (P
renum, 1974)). This TS
The FZ method is generally applied to decomposed molten compounds and solid solution single crystals. For example, if the phase diagram as shown in FIG. 12 (a) is clarified for the compound AB, the compound decomposes at the temperature T ₁ and becomes a liquid phase composition of A and p in the solid phase. Therefore, if a single crystal of this compound is to be grown, it must be grown at a temperature of T ₁ or lower.

Below the temperature T ₁ , solid AB is in equilibrium with the liquid phase of the composition on the liquidus up to the eutectic temperature. The TSFZ method utilizes this point. That is, a composition of s in equilibrium with solid AB was prepared as shown in FIG.
Sandwiched between the raw material sintered rod and the seed crystal,
The composition of s is first melted and fused with the raw material sintered rod and the seed crystal. After that, when the whole is slowly lowered, the composition AB starts to precipitate on the seed crystal. When this becomes steady, the composition AB of the raw material is dissolved, the composition AB is deposited on the seed crystal, and the single crystal of the composition AB can be grown. That is, the TSFZ method is a method of dissolving a raw material in a solvent using a solvent and precipitating a predetermined substance from the solvent. On the other hand, the slow cooling floating zone melting method (Slow Cooling
Floating Zone Method; SCFZ
Method) is used to create a phase diagram, but in this SCFZ method, if one with a certain composition is melted and the melting zone is separated while cooling, the ones with higher melting points will solidify in sequence. If you analyze it, you can make a phase diagram by showing which phase comes out first and then what.

The superconducting oxide single crystal according to the present invention is formed by utilizing the above-mentioned TSFZ method. The heating furnace used for growing the single crystal by the TSFZ method is provided with an infrared concentrated heating furnace, in particular, a mono-elliptical or bi-elliptical spheroidal mirror as shown in FIGS. It is preferable to use an infrared intensive heating furnace. Then, the inventors of the present invention have made La ₂ O ₃ shown in FIG.
According to the -CuO-based phase diagram, Sr is La when solid-soluted.
When it is considered that it is replaced with, the La _{2 -x} Sr _x CuO ₄
It has been found that the crystal of No. ₂ can be grown by referring to the La ₂ O ₃ —CuO system phase diagram. For example, FIG. 14 shows LaO.
_{It is a 1.5-} CuO type | system | group phase diagram.

Here, a preliminary experimental examination result in the present invention will be described. First, 80 mol of La ₂ O ₃
%, CuO 20 mol% composition was dissolved in an oxygen atmosphere of 0.1 MPa to identify a molten product. As a result, a mixture of La ₂ CuO and La ₂ O ₃ was formed. From the phase diagram, this composition has La ₂ CuO ₄ and Cu.
A mixture of O should be generated, but it is considered that generation of La ₂ O ₃ was recognized because CuO was evaporated and the composition was shifted to the La ₂ O ₃ side. Therefore, when the oxygen gas pressure was set to 0.2 MPa for the purpose of preventing the evaporation of CuO, it was confirmed that the molten product was a mixture of La ₂ CuO ₄ and CuO. From this, when growing a single crystal,
It has been found that a good single crystal is generated when the oxygen gas atmosphere during the growth is pressurized to 0.2 MPa or more.

When the oxygen gas is pressurized to 0.2 MPa or more, the evaporation is considerably suppressed as compared with the case of 0.1 MPa.
Experiments revealed that ₂ CuO ₄ and CuO were produced. From this result, in the present invention, an infrared concentrated heating furnace was used to perform crystal growth in a pressurized oxygen atmosphere of 0.15 MPa or more, preferably 0.2 to 0.25 MPa. However, when crystals are grown for a long time, CuO evaporates and adheres to the shaft and the quartz tube. The growth rate is preferably 0.5 to 3 mm / h. If the growth temperature is less than 1100 ° C, melting is insufficient, and
If the temperature exceeds 300 ° C, other phases will precipitate, so
1100 to 1300 ° C is preferable.

From the above experimental results, in the present invention, La-S
r-Cu-O system, Nd-CeCu-O system, Y-Ba-C
The growth conditions for the u-O-based or Bi-Ca-Ba-O-based crystals were: oxygen pressure: 0.15 MPa or higher; growth temperature: 1100 to 1300 ° C; growth rate: 0.3 to 3 mm / h. Under the above formation conditions, a single crystal of the superconducting oxide of the present invention has a diameter of 5 mm or more and a length of 40 mm or more, and the physical properties of these superconducting oxides are investigated by using the obtained single crystal. It became possible to do. Hereinafter, it will be described in more detail based on examples.

[0018]

1 and 2 are explanatory views of an infrared concentrated heating furnace having mono-ellipsoidal and bi-elliptical spheroidal mirrors used for producing a superconducting oxide single crystal of the present invention. In both figures, 1 is a mono-elliptical rotary mirror, 1a is a bi-elliptical rotary mirror, 2 is an infrared lamp (halogen lamp or xenon lamp), 3 is a solvent, 4 is a sintering raw material rod, 5 is an upper rotary shaft,
6 is a seed crystal, 7 is a lower rotary shaft, 8 is a transparent quartz tube, 9 is a lens, 10 is a screen, 11 is an atmospheric gas inlet, 12
Is the atmosphere gas outlet.

An embodiment of crystal growth according to the present invention will be described with reference to FIG. Bi-elliptical rotary mirror 1a
Is gold-plated to reflect infrared rays efficiently and to have durability, and an infrared lamp consisting of a halogen lamp or a xenon lamp of 1.5 kW is used as a heating light source for the outer focus of the bi-elliptical rotary mirror 1a. 2 is arranged, and the infrared ray emitted from this is focused on another focal position in the central portion. The solvent 3 is arranged at this focus position and is heated by the collected infrared rays. The temperature can be adjusted to 0 to 2150 ° C. by raising or lowering the voltage of the infrared lamp 2.

A sintering raw material rod 4 is suspended above the solvent 3 by an upper rotary shaft 5. A seed crystal 6 is supported by a lower rotary shaft 7 below the solvent 3, and the upper rotary shaft 5 and the lower rotary shaft 7 can be moved simultaneously. The spacing can be adjusted freely, and each rotating shaft can be rotated independently. Since the periphery of the solvent 3 is shielded from the outside air by the transparent quartz tube 8, the atmosphere and its pressure can be changed. For example, oxygen can be sealed from the atmospheric gas inlet 11 and oxygen pressure can be applied. Further, the lens 9 projects the condition of the melting zone on the screen 10, so that the crystal can be grown while observing the melting condition of the crystal. In addition, compressed air is blown into the bi-ellipsoidal mirror 1a to cool the lamp of the heating source, and to prevent overheating of the ellipsoidal mirror, and the holding part of the rotary shaft is provided with conduction heat and convection heat in the melting zone. It is water-cooled to prevent it. Hereinafter, an example in which a single crystal is grown using the apparatus shown in FIG. 2 will be described.

Example 1 As a starting material, a purity of 99.
Using 9% of La ₂ O ₃ , SrCO ₃ and CuO (both manufactured by Furuuchi Chemical Co., Ltd .: purity of 99.9%), these reagents were used in a stoichiometric amount of La _2−x Sr _x CuO ₄ (x = 0.15). Theoretical composition ratio, and wet-mixing with ethanol, followed by firing in air at 850 ° C. for 12 hours. Next, the calcined raw material is crushed and packed in a commercially available rubber balloon, and 1 ton / cm
^After applying a pressure of ² , by a so-called rubber press method of forming into a round bar shape having a diameter of 5 mm and a length of about 50 mm, it is sintered in oxygen at 1100 to 1200 ° C. for 12 hours, and this is La _1.85 Sr _{0. A} sintering raw material rod 4 having a composition of _.15 CuO ₄ was used. The solvent has an Sr / (La + Sr) ratio of 0.0
75 to 0.10, and weighed to a composition of 55 to 80 mol% CuO, CuO is 78 mol% and La ₂ O ₃ is 21.8.
A material having a composition of mol% and Sr of 0.02 mol% was produced by the same method as the sintering raw material rod 4.

For growing a single crystal, a bi-elliptical infrared concentrated heating furnace shown in FIG. 2 in which two 1.5 kW halogen lamps were used as infrared lamps 2 was used. The growth conditions were a growth rate of 1.0 mm / h, and a growth atmosphere of a gas pressure of 2 kg / cm ² (0.2) to prevent evaporation of CuO (copper oxide).
(MPa) pure pressurized oxygen. Also, in order to reduce the number of nuclei by making the melt thin and reducing the number of crystal nuclei,
A seed crystal was grown by necking growth, and the crystal was grown in the a-axis direction.

A photograph of the appearance of the produced crystal is shown in FIG. As is clear from FIG. 3, a black single crystal having a diameter of 6 mm and a length of 40 mm was obtained, and a round bar-like material having a metallic luster was obtained. Further, facets are observed in the growth direction on the surface of the grown crystal. Figure 5 shows a back Laue photograph of the facets. When the grown crystal was evaluated by the X-ray back surface Laue method, sharp spots were observed as shown in FIG. 5, and it was confirmed that the crystal was a single crystal. It has also been confirmed that the facets observed on the surface of the grown crystal are (001) faces.

In addition, the result of measuring the distribution of the mosaic structure by the neutron scattering experiment was 0.2 degrees or less, indicating that the single crystal was a good quality. The composition of the grown crystal in the diameter direction and the growth direction was analyzed by EPMA, and the composition was almost the same and uniform. Table 2 shows the quantitative analysis results using EPMA and the measurement results of the lattice constant by the powder X-ray diffraction method.

[0025]

[Table 2] As seen in Table 2, the composition of the grown crystal is La
_{It was 1.86} Sr _0.14 CuO ₄ , the amount of La was larger than that of the raw material rod, and the amounts of Sr and Cu were less than those of the raw material rod in the crystal.

Next, the results of evaluating the superconductivity of the obtained single crystal will be described. The electric resistance measurement result of the grown crystal is shown in FIG. As shown in FIG. 4, the critical temperature T
_konset (called superconducting transition onset temperature T _c ) is 3
Temperature ΔT at which electric resistance is completely 0 ohm at about 7K
_{The end} (referred to as ΔT _c ) was 30 K, indicating superconductivity. Further, FIG. 6 shows the temperature change characteristics of the electrical resistance of the grown crystal in the a-axis and c-axis directions. As is clear from FIG.
The electrical resistance in the a-axis direction (Cu-O plane) is several hundred times smaller than that in the c-axis direction, and it exhibits metallic behavior with temperature change. However, the temperature change of the resistance in the c-axis direction is metallic up to about 200 K, but shows a semiconductor-like behavior at temperatures below that. Also, the behavior around 200 K seems to correspond to the tetra-> ortho transition. As described above, it was revealed that the grown crystal exhibits large anisotropy.

Example 2 A grown crystal (a) obtained by the same method as in Example 1 and a grown crystal (b) obtained by annealing the grown crystal (a) in oxygen at 500 ° C. for 50 hours. ) And, the Meissner effect was measured. The results are shown in FIG. 7 and a summary thereof. T _c ΔT _c grown crystal (a) 31.5K 18.0K grown crystal (b) 35.0K 23.5K As shown in FIG. 7, all show good superconductivity, but grown crystal (b) In both cases, the starting temperatures T _c and ΔT _c both became higher, and the annealing effect was recognized.

[Example 3] First, Nd-Ce-Cu-O
Essential _Nd 2 _O 3 -CuO over to synthesize a single crystal of the system
The _two phase diagrams of the system, Nd ₂ O ₃ —CeO ₂ —CuO system, were investigated. Each of the powders of Nd ₂ O ₃ , CeO ₂ and CuO was weighed so as to have a predetermined composition, mixed in a mortar for about 30 minutes, and baked at 850 ° C. for 24 hours. The fired sample was examined for phase change at high temperature by a differential thermal balance TG-DTA. The measurement conditions are heating and cooling at a rate of 5 ° C.
/ Min, Al ₂ O ₃ powder was used as a standard sample, and the atmosphere was 0.1 MPa oxygen. Further, the fired sample was formed into a round bar having a diameter of 8 mm and subjected to isostatic pressing at 100 MPa, and then Nd ₂ O ₃ : CuO = 1: 1.
Sample is 1200 ℃, sample of other composition is 100
Sintered at 0 ° C. In the melting test, the single elliptical infrared concentrated heating furnace shown in FIG. 1 using a 1.5 kW halogen lamp as the heating light source 2 was used to melt and solidify samples of various compositions by the above-mentioned SCFZ method.

The sample obtained by this SCFZ method is
Observation by EPMA and composition analysis were performed. Nd ₂
As a result of analyzing a sample having a composition of O ₃ / CuO = 1/1 by TG-DTA, endothermic peaks appeared at 1050 ° C. and 1270 ° C. when the temperature was raised. Further, the molten sample was examined by powder X-ray diffraction _method, it was also observed _Nd 2 _{O 3} in addition to the Nd 2 CuO _4. Then, the sintered body of 60 mol% CuO is added to S
When melted and solidified by the CFZ method and observed by EPMA, Nd ₂ O ₃ was found in the primary crystal part and Cu was found in the tip part.
There were many O and Cu ₂ O, respectively. From this,
Nd ₂ CuO ₄ is 1270 ° C. or higher, and Nd ₂ O ₃ + Li
It decomposes and melts into a quid, and the eutectic point of Nd ₂ CuO ₄ is 10
It was found to be 50 ° C.

Next, in order to determine the liquid phase composition in equilibrium with Nd ₂ CuO ₄ , TG-DTA was performed on a sample having a CuO rich composition and found to be 79 mol% Cu.
The temperature at which the melt solidifies from a sample of O or higher begins to drop, and
It was closest to the eutectic point at 1 mol% CuO. Then, when a sample of 85 mol% CuO was melted and solidified by the SCFZ method and observed by EPMA, Nd ₂ O _{3 was obtained.}
Was not generated, and the primary crystal was Nd ₂ CuO ₄ . That is,
It was found that there is a liquidus line in which Nd ₂ CuO ₄ and the melt are in equilibrium at 79 to 91 mol% CuO. Also, C
With the uO rich composition, there were two endothermic peaks when the temperature was raised, but three exothermic peaks when the temperature was lowered after melting. Of the three peaks, the two on the high temperature side corresponded respectively to the endothermic peaks at the time of temperature rise.
There is no one corresponding to the third peak near 0 ° C. Further, this peak has a higher intensity as the amount of the solvent CuO increases, so it is considered that this peak is due to Cu ₂ O generated by the decomposition of CuO when the sample melts. FIG. 8 shows a phase diagram of the Nd ₂ O ₃ —CuO system derived from these facts.

Next, (92.5% Nd ₂ O ₃ + 7.5%
CeO ₂ ) / CuO = 30/70 and 15/85 Two sintered bodies were melted and solidified by the SCFZ method, and the part was EPM
Observed by A. A 70 mol% CuO sample was used as a primary crystal, and a solid solution of Nd _2−x Ce _x O _{3 + δ} was precipitated.
Further, in the case of the 85 mol% CuO sample, there was no precipitation of solid solution, and Nd _1. The phase of ₈₅ Ce _0.15 CuO _4-y precipitated first. In addition, from the result of TG-DTA,
Although there was no change in the eutectic point, the peritectic point was 1315 ° C, which was about 45 ° C higher than that of the Nd ₂ O ₃ —CuO system. The composition range of the liquidus line in which Nd _1.85 Ce _0.15 CuO _4-y and the melt are in equilibrium is 78 mol% C.
It was found that there was a slight spread from uO to 91 mol% CuO. In addition, also in the sample to which Ce was added, an exothermic peak when Cu ₂ O was solidified was observed at around 1000 ° C. From the above results, the state diagram of _{Nd 2 O} 3 -CeO 2 -CuO system in FIG. _9, expressed in _{Nd 2 -x Ce x O 3 +} δ -CuO system pseudo two-component.

FIG. 9 shows 79 to 9 by the TSFZ method.
By using a solvent of 1 mol% CuO, Nd
It shows that it is possible to grow a single crystal of _2-x Ce _x CuO ₄ . Hereinafter, Nd _2-x with Ce = 0.15
The result of growing a single crystal of Ce _x CuO ₄ by the TSFZ method is shown. The same apparatus as in Example 1 was used, and Nd _2-x C
The oxide powders of Nd ₂ O ₃ , CeO ₂ and CuO were weighed in proportion to the stoichiometric composition ratio of e _x CuO ₄ , mixed and fired at 850 ° C. for 24 hours, and then the same as Example 1. Was formed into a round bar shape having a diameter of 6 mm and a length of about 50 mm by the Laper Press method, and then sintered in oxygen at 1100 to 1200 ° C. for 12 hours to obtain a sintering raw material bar 4. Next, the solvent is 80
After weighing to a composition of mol% CuO, it was synthesized in the same manner as the sintering raw material rod 4.

The same bi-elliptical infrared concentrated heating furnace as in Example 1 was used for growing the single crystal. The growing conditions were such that the growing speed was 0.5 to 3.0 mm / h, and the growing atmosphere was a pure oxygen gas pressure of 0.1 to 0.25 MPa. Further, a seed crystal was grown by necking growth, and the crystal was grown in the a-axis direction. As a result, the single crystal of _{Nd 2-x} Ce _x CuO _4, which is grown, a large amount of _{Nd 1. 48} Ce _0.52 O _{3 + δ}
It contained a solid solution of and was brittle. 85 mol in FIG.
Of% when grown with CuO _Nd 2-x _Ce x Cu
Training of O ₄ shows a structure photograph of the single crystal. Growing crystal is 5mm
It was 50 mm in diameter and black with no metallic luster and had parallel cleavage planes along the c-plane.

Although the single crystal contained a small amount of subgrain boundary structure and some CuO, a single crystal of about 2 × 3 × 5 mm ³ was obtained. The composition of this crystal was determined to be Nd _1.86 Ce _0.14 CuO _{4 as} a result of quantitative analysis by EPMA, which was slightly lower in Ce than the supplied Nd _{1.8 5} Ce _0.15 CuO ₄ . . The precipitation of CuO occurred as a result of the composition change of the melting zone, and changed to the composition on the Cu rich side. Therefore, it can be seen that the optimum composition of the solution is 80 to 85 mol% CuO.

Next, the magnetism of the grown crystal was evaluated. No Meissner effect was obtained from the grown Nd _1.86 Ce _0.14 CuO ₄ crystal. Single crystals of _{Nd 2-x} Ce _x CuO ₄ annealed under reducing conditions become superconductors were also grown in TSFZ method in deoxygenated within N
Although single crystals of d _2-x Ce _x CuO ₄ has been reported that Tc has the following superconducting 10K, single crystal according to the study, because it was grown in oxygen within to prevent evaporation of CuO , Did not become superconducting. Taking the above results into consideration, the obtained Nd _1.86 Ce _0.14 CuO ₄ crystal was annealed in gaseous nitrogen at 900 ° C. for 70 hours, and then the Meissner effect was examined. The result is shown in FIG. FIG. 11 is a characteristic diagram showing the temperature dependence of the magnetization of the annealed crystal of Nd _1.86 Ce _0.14 CuO ₄ . As shown in FIG. 11, Nd _1.86 Ce _0.14 CuO ₄
The Tc of the annealed crystal of No. 1 was 19 K, and its temperature was lower than that of the previously reported single crystal of Nd _2−x Ce _x CuO ₄ . The temperature drop seems to be due to the precipitation of CuO in the grown crystal and the annealing conditions.

[0036] From the above description, the manufacturing conditions according to the present invention, it _{La 2-x} Sr x CuO ₄ and _{Nd 2-x} Ce _x CuO ₄ exhibits superconductivity is possible large growing of the single crystal Was shown, but YBa ₂ Cu ₃ O _7-x , B
iSrCaCu ₂ O _x , Tl ₂ Ba ₂ Ca ₂ Cu ₃ O _x
With respect to etc., a superconducting single crystal can be obtained under similar manufacturing conditions.

Further, in the single crystal of the superconducting oxide according to the present invention, the crystal is tetragonal and the crystal growth direction is a.
The feature is that it is an axis. However, since the characteristic that it behaves like a semiconductor by flowing a current in the c-axis direction is expressed by this, it can be expected to be applied to a switching element or the like in a cryogenic system.

[0038]

As described above, according to the present invention, it is a large-sized single crystal of high quality capable of elucidating the superconductivity of a superconducting oxide. Physical properties such as anisotropy of electrical properties can be strictly measured, and there is a great effect that the superconductivity can be elucidated from information on anisotropy and contribute to the research of the mechanism of superconductivity development. Furthermore, since the single crystal of the superconducting oxide according to the present invention is tetragonal and the crystal growth direction is the a-axis, the above-mentioned anisotropy is definitely identified. , If a current is passed in the c-axis direction, a characteristic of semiconductor behavior is exhibited, so that an excellent effect that it can be expected to be applied to, for example, a switching element in a cryogenic system can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory view of a single elliptical infrared concentrated heating furnace for producing a single crystal of the present invention.

FIG. 2 is an explanatory view of a bi-elliptical infrared concentrated heating furnace for producing the single crystal of the present invention.

FIG. 3 is a structural photographic diagram of a grown single crystal in Example 1 of the present invention.

FIG. 4 is an electric resistance-temperature characteristic diagram showing superconductivity of a grown crystal.

FIG. 5 is a rear Laue crystal photograph of the facet.

FIG. 6 is a characteristic diagram showing temperature change characteristics of electric resistance in the a-axis and c-axis directions of a grown crystal.

7 is a characteristic diagram showing the Meissner effect of the single crystal of Example 2. FIG.

FIG. 8 is a phase diagram of Nd ₂ O ₃ —CuO system.

FIG. 9 is a phase diagram of the Nd ₂ O ₃ —CeO ₂ —CuO system.
It is a state diagram showing in _{Nd 2-x Ce x O 3} + δ -CuO system pseudo two-component.

FIG. 10 is a structural photographic diagram of a grown single crystal of Example 3.

11 is a diagram showing the Meissner effect of the single crystal of Example 3. FIG.

FIG. 12 is a schematic phase diagram and TSF of decomposed molten compound AB.
It is a principle explanatory view of Z method.

FIG. 13 is a phase diagram of a La ₂ O ₃ —CuO system in air.

FIG. 14 is a LaO _1.5 —CuO system phase diagram.

[Explanation of symbols]

1 Single Elliptical Rotating Mirror 7 Lower Rotating Axis 1a Twin Elliptic Rotating Mirror 8 Transparent Quartz Tube 2 Infrared Lamp 9 Lens 3 Solvent 10 Screen 4 Sintering Raw Material Rod 11 Atmospheric Gas Inlet 5 Upper Rotating Axis 12 Atmospheric Gas Outlet 6 Seed Crystal

Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location H01B 12/00 ZAA 13/00 565 D

Claims (2)

[Claims] 1. La-Sr-Cu-O system, Nd-Ce-
Cu-O system, Y-Ba-Cu-O system or Bi-Ca-B
an a-O system crystal, wherein the crystal is a tetragonal system,
A single crystal of a superconducting oxide, wherein the crystal growth direction is the a-axis. 2. La-Sr-Cu-O system, Nd-Ce-
Cu-O system, Y-Ba-Cu-O system or Bi-Ca-B
A method of using a single crystal of a superconducting oxide, characterized in that a current is caused to flow in a c-axis direction of a tetragonal superconducting oxide single crystal among a-O type crystals.