JP2684432B2 - Superconducting oxide single crystal and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a superconducting oxide having a critical temperature at high temperature, particularly Nd.
_2-x Ce _x CuO ₄ , YBa ₂ Cu ₃ O _7-x , BiSrCaCu ₂ O _x , Tl ₂ Ba ₂ Ca ₂ Cu ₃
The present invention relates to a single crystal such as O _x and a method for producing the same.

[Prior Art] Since the discovery in 1986 by Drs. JG Bedonorz and KA Muller that even oxides exhibit superconducting properties at high temperatures, many researches on superconducting oxides have been conducted all over the world.

Some oxides such as 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 Cu ₃
It is known that O _{x and the} like exhibit superconductivity at a higher critical temperature than conventional metal-based superconducting substances, although the density of states of electrons is extremely low.

Most of the studies on these oxides deal with sintered materials and thin films, and quite detailed studies have been conducted on the relationship between the crystal structure and the chemical composition and the critical temperature. However, the established principle has not been found yet regarding the mechanism of the superconductivity of these oxide superconductors.

Most of the oxide superconducting materials reported to date have a perovskite lattice as a basic structure, and unlike metal or alloy superconducting materials, belong to tetragonal or orthorhombic rather than cubic. Therefore, information on anisotropy cannot be obtained from the physical properties of the sintered material, which is an aggregate of polycrystals, and it is difficult to obtain information in the thickness direction on a thin film, which makes it difficult to establish the mechanism of superconductivity development. .

To measure the physical properties such as anisotropy of magnetic and electrical properties of oxides precisely, to obtain information on anisotropy, and to elucidate its superconductivity, a large single crystal with good quality is required. Therefore, for this reason, it is desired to grow a large crystal of good quality.

Single crystals of oxide high-temperature superconducting materials that have been reported to have been grown to date include La-Sr-Cu-O-based and Nd-Ce-Cu-
O-based, Y-Ba-Cu-O-based, Bi-Ca-Ba-CuO-based, and the like. Since most of these substances are considered to be decomposed and melted compounds, the melting and solidification methods such as the pulling method and the bridge machine method, 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, which is a devised version of the flux method. For Bi-based single crystals, the floating zone method (floating zone method) was used by Takekawa et al.
Attempts using thod) have been reported. J.Cryst.Grow
th, 92 (1988) 687. Also, a eutectic composition of La ₂ CuO ₄ and CuO is reported as shown in Table 1 below. L.Trouilleux.GD
halenne and A. Revcolevschi: Cryst.Growth, 91 (1988)
268 The solvents used in the flux method are often
CuO is called self-flux, and after crystal growth, the flux and the generated crystal are mechanically separated, and it is difficult to separate the solvent and the grown crystal.

However, in the example of a lanthanum-based La _2-x A _x CuO ₄ single crystal,
It grows in flux and scoops the crystals that settled at the bottom of the crucible, trying to separate it 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 content of the flux is observed. Further, thin plate-like crystals are 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, and the like, which have been reported so far regarding the lanthanum-based single crystal.

As can be seen from Table 1, most of the grown crystals are plate crystals as described above. The size of the crystal grown by the top seed method is as large as 25 × 25 × 5 mm, but the critical temperature is very low. This is probably because the solid solution of Sr (Ba) is less than the raw material composition. Also, in the example by the floating zone method shown at the end of Table 1, the crystals are large,
The critical temperature is higher than other methods, but the raw material composition is Cu
Since it has a eutectic composition with O, and the grown crystal is a eutectic containing CuO, it cannot be said to be a single-phase crystal.

[Problems to be Solved by the Invention] As described above, the crystal size of the conventional superconducting oxide is not so large. If it is large, the inclusion of flux is observed, and it is a thin plate crystal in the c-axis direction. Therefore, it is difficult to strictly measure physical properties such as anisotropy of magnetic and electrical properties of oxides, and it is difficult to obtain information on anisotropy, and it is difficult to construct a mechanism for manifesting superconductivity.

Therefore, an object of the present invention is to obtain a large-sized oxide single crystal having high quality and superconductivity for clarifying the superconductivity of an oxide.

[Means for Solving the Problems] A single crystal of a superconducting oxide according to the present invention is an oxide that exhibits anisotropy and superconductivity in a tetragonal system, and has a substantial stoichiometric composition. The same burning raw material rod as 0.15MPa
Dissolved in a solvent mainly composed of copper oxide placed in an infrared concentrated heating furnace under the above oxygen pressure, a crystal obtained by depositing on a seed crystal, wherein the crystal is a tetragonal system and seed growth direction of the crystal is characterized in that an a-axis, the superconducting _{oxide, Nd 2-x Ce x CuO} 4, YBa 2 Cu 3 O 7-x, BiSrCaCu 2 O x, Tl 2 It is a single crystal of superconducting oxide that is Ba ₂ Ca ₂ Cu ₃ O _x and has a diameter of 5 mm or more and a length of 40 mm or more.

The method for producing a single crystal of a superconducting oxide according to the present invention, the solvent disposed between the raw material oxide and the seed crystal, the seed crystal in a state of being heated and melted and in contact with the raw material oxide and the seed crystal. A method for producing a single crystal of a superconducting oxide, in which a relative position of a heating source is moved and a starting oxide is deposited on a seed crystal in a controlled atmosphere to precipitate an oxide having substantially the same composition as the starting oxide, The stoichiometric composition of the raw material oxide is substantially the same as that of the superconducting oxide, the solvent is mainly copper oxide, and the oxygen pressure of the atmosphere is
And characterized in that at 0.15MPa or more, and the superconducting _{oxide, Nd 2-x Ce x CuO} 4, YBa 2 Cu 3 O 7-x, BiSrCaCu 2 O x, Tl 2 Ba 2 Ca ₂ Cu ₃ O _x , further, in growing the single crystal, after dissolved in a solvent of 55-91 mol% CuO composition, oxygen pressure: 0.15 MPa or more, growth temperature: 1100 ~ 1300 ℃ growth rate: 0.5 ~ Under a growth condition of 3 mm / h, a single crystal is grown in a large size. A seed crystal is used for growing the single crystal, and the seed crystal grows in the a-axis direction by necking growth. It is a method for producing a single crystal of a superconducting oxide, and is a method for producing a single crystal of a superconducting oxide, which is characterized in that the single-crystallized crystal is further annealed in oxygen or nitrogen.

[Operation] The present invention is based on the solvent transfer floating zone method: Traveling Solvent F
By the loating zone method (TSFZ method), a superconducting oxide single crystal is grown and enlarged.

About this TSFZ method, GAWolff: “CRYSTALGROWTH
Theory and Techniques pp 194-230 "GHL Goodman Ed,
(Prenum, 1974), the TSFZ method is generally applicable to decomposed molten compounds and solid solution single crystals. For example, the phase diagram shown in FIG.
, The compound decomposes at the temperature T ₁ into a liquid phase composition of A and p in the solid phase. If a single crystal of this compound is to be grown, it must be grown at a temperature of T ₁ or lower.

At temperatures below the temperature T ₁ , the solid AB is in equilibrium with the liquid phase of the composition on the liquidus up to the eutectic temperature. I used this point
This is the TSFZ method.

That is, the composition of s in equilibrium with the solid AB was sandwiched between the raw material sintered rod and the seed crystal, as shown in FIG. 12 (b), and the composition of s was first prepared. It is melted and fused with the raw material sintered rod and the seed crystal. After that, when the whole is slowly lowered, the composition AB begins to precipitate on the seed crystal. If this becomes steady, the composition AB of the raw material is dissolved, the composition AB is deposited on the seed crystal, and a single crystal of the composition AB can be grown.

That is, the TSFZ method uses a solvent, dissolves the raw materials in the solvent, and precipitates a predetermined substance from the solvent.
On the other hand, Slow Cooling Floating Zo
ne method; called SCFZ method) is used to create a state diagram,
In this SCFZ method, if one of a certain composition is melted and the molten zone is separated while cooling, the ones with higher melting points solidify in sequence, so when analyzing it later, which phase appears first. Then, what you can do next is to make a state diagram.

 The present invention utilizes this TSFZ method.

The heating furnace used for growing the single crystal is an infrared concentrating heating furnace, particularly an infrared concentrating furnace using a single elliptical or bi-elliptical spheroidal mirror as shown in FIG. 1 and FIG. A heating furnace is desirable.

The present invention, oxide _{Nd 2-x Ce x CuO 4} , YBa 2 Cu 3 O 7-x, BiS
Targeting rCaCu ₂ O _x or Tl ₂ Ba ₂ Ca ₂ Cu ₃ O _x , La _2-x A
La _2-x A _x CuO ₄ without _x CuO ₄ (A: Sr, Ba)
The characteristics of (A: Sr, Ba) are Nd _2-x Ce _x CuO ₄ , YBa ₂ Cu ₃ O
It was realized by the finding that it is similar to _7-x , BiSrCaCu ₂ O _x or Tl ₂ Ba ₂ Ca ₂ Cu ₃ O _x . In the actions and examples described later, mainly La _2-x A _x CuO
₄ (A: Sr, Ba), etc. are mainly described, but these are Nd _2-x Ce _x CuO ₄ , YBa ₂ Cu ₃ O _7-x , BiSrCaCu ₂ O _x or Tl.
₂ Ba ₂ Ca ₂ Cu ₃ O _{x It} is just for convenience (relationship of owned data) to explain the characteristics of La _{2 x} A _x CuO ₄ (A: S
r, Ba) are not included in the present invention.

From the phase diagram of the La ₂ O ₃ —CuO system shown in FIG. 13, the inventors of the present invention consider that Sr substitutes for La when it forms a solid solution.
_2-x A _x crystal growth of CuO ₄ was found that the La ₂ O ₃ -CuO phase diagram may be helpful.

Figure 14 is a phase diagram of the LaO _1.5- CuO system.

As a preliminary experiment of the present invention, La ₂ O ₃ 80 mol%, CuO20mo
The l% of the composition is melted in an oxygen atmosphere at 0.1 MPa, from the state diagram mixture was produced of the identifying molten product La ₂ CuO and La ₂ O _3, in this composition the La ₂ CuO ₄ A mixture of CuO should be formed, but it is considered that the formation of La ₂ O ₃ was recognized because CuO was evaporated and the composition was shifted to the La ₂ O ₃ side.

Therefore, as a result of setting the oxygen gas pressure to 0.2 MPa in order to prevent the evaporation of CuO, the molten product was a mixture of La ₂ CuO ₄ and CuO. From this, it was found that, when single crystallizing, a good crystal can be grown by pressurizing the atmosphere during growth with oxygen gas at 0.2 MPa or more.

Evaporation is 0.1MPa when oxygen gas is pressurized above 0.2MPa
It was clarified by experiments that La ₂ CuO ₄ and CuO were generated, which was suppressed much more than when.

From this result, in the present invention, using an infrared concentrated heating furnace, the atmosphere is 0.15MPa or more, preferably 0.2 ~ 0.25MPa.
The crystal is grown in the pressurized oxygen atmosphere. However, when the crystal is 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.
If the temperature exceeds 00 ° C, other phases will begin to precipitate.
-1300 ° C is preferred.

From the above, in the present invention, the growth conditions were oxygen pressure: 0.15 MPa or more, growth temperature: 1100 to 1300 ° C., growth rate: 0.5 to 3 mm / h. As a result, a single crystal of the superconducting oxide of the present invention having a diameter of 5 mm or more and a length of 40 mm or more was obtained, which made it possible to investigate and study the physical properties of these superconducting oxides.

One of the achievements is that the crystal is tetragonal and the growth direction of the seed crystal is the a-axis, so if a current is passed in this direction, the temperature will rise at the critical temperature while maintaining the normal metallic behavior. Superconducting properties can be obtained.

 Next, examples will be described.

Example FIG. 1 and FIG. 2 are explanatory views of an infrared concentrated heating furnace having a single elliptical or bielliptical spheroidal mirror used for producing a superconducting oxide single crystal of the present invention.

In the figure, 1 is a mono-elliptical rotary mirror, 1a is a bi-elliptical rotary mirror, 2 is an infrared lamp (halogen 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, and 12 is an atmospheric gas outlet.

 An embodiment of the present invention will be described with reference to FIG.

The bi-elliptical rotary surface mirror 1a is plated with gold in order to efficiently reflect infrared rays and to have durability, and as a heating light source for the outer focal point of the bi-elliptical rotary surface mirror 1a, 1.5kW is used.
Infrared lamp 2 such as a halogen or xenon lamp is arranged, and infrared rays emitted from the infrared lamp 2 are focused on another focal point in the central portion.

The solvent 3 is arranged at this focal point. The temperature can be adjusted from 0 ° C to 2150 ° C by raising or lowering the voltage of the lamp.

Above the solvent 3, a sintering raw material rod 4 is suspended on 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 at the same time. Can be freely adjusted, and each rotating shaft can be rotated independently.

The transparent quartz tube 8 shields the surroundings of the solvent 3 from the outside air, so that the atmosphere and its pressure can be changed. For example, oxygen can be sealed from the atmosphere gas inlet 11 to apply oxygen pressure.

In addition, the condition of the melting zone is displayed by the lens 9 on the screen 10.
Since it is shown above, it is possible to grow while observing the melting state of the crystal.

In addition, in order to cool the lamp of the heating source by blowing compressed air into the ellipsoidal mirror 1, to prevent overheating of the ellipsoidal mirror, and to prevent conduction heat and convection heat in the melting zone in the holding portion of the rotating shaft. It is designed to be water cooled.

Next, an example in which a single crystal is grown using the above apparatus will be described.

[Example 1] As starting materials, La ₂ O ₃ , SrCO ₃ and CuO having a purity of 99.9% were used.
(Both manufactured by Furuuchi Kagaku Co., Ltd .; purity 99.9%), these reagents were weighed to a La _2-x Sr _x CuO ₄ (x = 0.15) stoichiometric composition ratio and wet-mixed with ethanol, It was calcined in air at 850 ° C for 12 hours.

Next, the calcined raw material is crushed and packed in a commercially available rubber balloon, and a pressure of 1 ton / cm ² (100 MPa) is applied to this, a diameter of 5 mm and a length of 5
After forming by a so-called rubber press method of forming into a round bar shape of about 0 mm, it was sintered in oxygen at 1100 to 1200 ° C. for 12 hours to obtain a sintering raw material rod 4 having a composition of La _1.85 Sr _0.15 CuO ₄ .

Solvent has Sr / (La + Sr) ratio of 0.075 to 0.10 and 55 to 80 mol% C
Weighed to the composition of uO, CuO 78mol%, La ₂ O ₃ 21.8mol% and Sr
A material having a composition of 0.02 mol% was manufactured by the same method as the raw material rod 4.

For growing a single crystal, a bi-elliptical infrared concentrated heating furnace shown in FIG. 2 using two 1.5 kW halogen lamps as a heating light source was used.

The growth conditions were a growth rate of 1.0 mm / h, and to prevent evaporation of copper oxide, the growth atmosphere was grown in pure pressurized oxygen with a gas pressure of 2 kg / cm ² (0.2 MPa).

Further, in order to reduce the number of nuclei in the melt by making the melt thin and reducing the number of crystal nuclei, a seed crystal is grown by necking growth, and a
Crystal growth was carried out in the axial direction.

A photograph of the produced crystals 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. Also, facets were observed in the growth direction on the surface of the grown crystal.

Figure 5 shows a backside Laue photograph of the facets.

When the grown crystal was evaluated by the X-ray back surface Laue method, as shown in FIG. 5, sharp spots were observed and it was confirmed that the crystal was a single crystal.

It was revealed that the facets on the surface of the grown crystal were (001) faces.

In addition, the distribution of the mosaic structure by the neutron scattering experiment is 0.2.
It was a good-quality single crystal below the temperature.

In addition, the composition of the grown crystal was uniform in the direction of diameter and the direction of growth by EPMA, and the composition was almost unchanged. Table 2 shows the quantitative analysis results using EPMA and the measurement results of the lattice constant by the powder X-ray diffraction method.

As shown in Table 2, the composition of the grown crystal is La _1.86 Sr.
_{It was 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 small in the crystal.

Next, superconductivity was evaluated.

The electric resistance measurement result of the grown crystal is shown in FIG. As shown in Fig. 4, the critical temperature T _conset (referred to as the superconducting transition start temperature T _c ) is 37th, and ΔT _end (referred to as ΔT _c ) at which the electric resistance is completely 0 ohm is 30 K. It showed conductivity.

Next, FIG. 6 shows the temperature change of the electrical resistance of the grown crystal in the a-axis and c-axis directions. As is clear from FIG. 6, the electric resistance in the a-axis direction (Cu-O plane) is several hundred times smaller than that in the c-axis direction, and shows a 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 at a temperature lower than that, it behaves like a semiconductor.

Also, the behavior around 200K seems to correspond to the tetra-> ortho transition. Thus, it was revealed that the grown crystal exhibited a large anisotropy.

[Example 2] A grown crystal (a) obtained in the same manner as in Example 1 and a crystal (a) obtained by annealing the obtained crystal (a) in oxygen at 500 ° C for 50 hours (Meissner) The effect was measured. The results are shown in FIG.

As shown in FIG. 7, all exhibited superconductivity and an annealing effect was observed.

Example 3 First, a phase diagram of Nd ₂ O ₃ —CuO system and Nd ₂ O ₃ —CeO ₂ —CuO system, which are indispensable for synthesizing Nd—Ce—CuO—O system single crystal, was 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 were such that heating and cooling were performed 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.

In addition, the fired sample is made into a round bar with a diameter of 8 mm and 100 MPa.
After isostatic pressing, the sample of Nd ₂ O ₃ : CuO = 1: 1 was sintered at 1200 ° C, and the other samples were sintered at 1000 ° C.

For the melting test, the single elliptical infrared concentrated heating furnace shown in Fig. 1 using a 1.5 KW halogen lamp as a heating light source was used.
Samples of various compositions were melted and solidified by the SCFZ method.

The sample obtained by this SCFZ method was observed by EPMA and its composition was analyzed.

As a result of TG-DTA analysis of a sample having a composition of Nd ₂ O ₃ / CuO = 1/1, endothermic peaks appeared at 1050 ° C and 1270 ° C when the temperature was raised. When the molten sample was examined by powder X-ray diffractometry, Nd ₃ O ₃ was found in addition to Nd ₂ CuO ₄ .

Then, when the sintered body of 60 mol% CuO was melted and solidified by the SCFZ method and observed by EPMA, Nd ₂ O ₃ was found in the primary crystal part,
And CuO and Cu ₂ O were present in the tip part in large numbers.

From this, Nd ₂ CuO ₄ can be used at temperatures above 1270 ℃ for Nd ₂ O ₃ + Li.
After decomposition and melting into quid, it was found that the eutectic point of Nd ₂ CuO ₄ was 1050 ° C.

Next, in order to determine the liquid phase composition in equilibrium with Nd ₂ CuO ₄ , TG-DTA was performed on samples with a CuO rich composition, and the temperature at which the melt solidified from 79 mol% CuO or higher samples began to fall. , 91mol% CuO, it was closest to the eutectic point.

When a sample of 85 mol% CuO was melted and solidified by the SCFZ method and observed by EPMA, Nd ₂ O ₃ was not produced and the primary crystal was Nd ₂ CuO ₄ . In other words, when 79 to 91 mol% CuO, N
It was found that there is a liquidus line where d ₂ CuO ₄ and the melt are in equilibrium.

In addition, when the CuO rich composition was used, there were two endothermic peaks when the temperature was raised and three exothermic peaks when the temperature was lowered after melting. Of the three peaks, the two on the high temperature side corresponded to the endothermic peaks during temperature rise,
There is no one corresponding to the third peak near ℃. further,
This peak increases in intensity as the solvent CuO increases, so when the sample melts, Cu
It seems that it is due to Cu ₂ O generated by the decomposition of O. Nd ₂ O derived from these things
A phase diagram of the _3- CuO system is shown in FIG.

Then (92.5% Nd ₂ O ₃ + 7.5% CeOC) / CuO = 30/70 and 15/85
The part of the sintered body obtained by melting and solidifying by the SCFZ method was observed by EPMA. The sample of 70 mol% CuO was Nd _2-x Ce _x
A solid solution of O _{3 + δ} was deposited.

In the case of the 85 mol% CuO sample, the solid solution was not precipitated and the Nd _1.85 Ce _0.15 CuO _4-y phase was precipitated first.

Also, from the results of TG-DTA, there was no change in the eutectic point, but the peritectic point was 1315 ℃, 45 ℃ than Nd ₂ O ₃ -CuO system.
It became higher. And, the composition range of the liquidus line where Nd _1.85 Ce _0.15 CuO _4-y and the melt are in equilibrium is 78 to 91 mol% CuO,
It turned out that it spread a little.

In addition, the exothermic peak when Cu ₂ O solidified near 1000 ° C was also observed in the sample with Ce added.

From the above, the phase diagram of the Nd ₂ O ₃ —CeO ₂ —CuO system is shown in FIG. 9 as a pseudo binary system of the Nd _2−x Ce _x O _{3 + δ−} CuO system.

This FIG. 9 shows that it is possible to grow a single crystal of Nd _2−x Ce _x CuO ₄ by the TSFZ method by using a solvent having a composition of 79 to 91 mol% CuO.

A single crystal of Nd _2-x Ce _x CuO ₄ with Ce = 0.15 was grown by the TSFZ method.

Using the same apparatus as in Example 1, the raw material rod 4 was Nd _2-x Ce _x.
Oxide powders of Nd ₂ O ₃ , CeO ₂ and CuO were weighed and mixed with the ratio of the stoichiometric composition ratio of CuO ₄ , mixed and fired for 24 hours at 850 ° C. Molded into a round bar with a diameter of 6 mm and a length of 50 mm by the press method, then in carbon 1100-1200 ℃
Sintering raw material rod 4 was obtained by sintering for 12 hours.

Next, the solvent was weighed to a composition of 80 mol% CuO, and then synthesized in the same manner as the raw material rod 4.

The same bi-elliptical infrared concentrated heating furnace as in Example 1 was used for growing the single crystal.

As for the growth conditions, the growth rate was 0.5 to 3.0 mm / h, the growth atmosphere was pure oxygen, and the gas pressure was 0.1 to 0.25 MPa. Also, seed crystals were grown by necking growth, and crystals were grown in the a-axis direction.

As a result, the grown Nd _2-x Ce _x CuO ₄ single crystal contained a large amount of a solid solution of Nd _1.48 Ce _0.52 O _{3 + δ} and was fragile.

Figure 10 shows Nd _2-x Ce _x when grown using 85 mol% CuO.
The structural photograph of the grown single crystal of CuO ₄ is shown.

The grown crystal was 5 mm in diameter and 50 mm in length, black with no metallic luster, and had parallel cleavage planes along the c-plane.

Although the single crystal contained a slight amount of subgrain boundary structure and some CuO, a single crystal of about 2 × 3 × 5 mm ³ was obtained. As a result of quantitative analysis by EPMA, the composition of this crystal was found to be Nd _1.86 Ce
It was determined to be _0.14 CuO ₄ , which was slightly less Ce than the feed Nd _1.85 Ce _0.15 CuO ₄ .

CuO precipitation occurs as a result of composition changes in the melt zone,
The composition changed to that on the Curich side. Therefore, it can be seen that the optimum composition of the solution is 80 to 85 mol% CuO.

 Next, the magnetic properties were evaluated.

The Meissner effect was not obtained from the grown Nd _1.86 Ce _0.14 CuO ₄ crystal.

The single crystal of Nd _2-x Ce _x CuO ₄ annealed in the reduced state became a superconductor and was grown by the TSFZ method in the deoxygenation zone.
The single crystal of Nd _2-x Ce _x CuO ₄ has been reported to have superconductivity with T _c of 10 K or less, however, the single crystal according to the present test shows that the single crystal of this test has an oxygen group to prevent evaporation of copper oxide. Since it was grown in, it was not superconducting.

In this way, the 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 results are shown in FIG. Figure 11 shows Nd _1.86 Ce
The temperature dependence of the magnetization of _0.14 CuO ₄ annealed crystals is shown.

As shown in FIG. 11, the T _c of the annealed crystal of Nd _1.86 Ce _0.14 CuO ₄ is 19 K, and the temperature is Nd _2-x Ce reported previously.
_It was lower than that of _x CuO ₄ single crystal. The temperature drop seems to be due to the precipitation of CuO in the grown crystal and the annealing conditions.

As described above, it has been clarified that Nd _2-x Ce _x CuO ₄ exhibiting superconductivity can be grown and enlarged in size of a single crystal by the production method of the present invention, but YBa ₂ Cu ₃ O _{7- X} , BiSrCaCu ₂ O _x , Tl
_The present invention can be similarly applied to ₂ Ba ₂ Ca ₂ Cu ₃ O _x .

[Effects of the Invention] The superconducting oxide single crystal of the present invention is of good quality for elucidating the superconducting property of the superconducting oxide, the crystal is tetragonal, and the seed crystal growth direction is the a-axis. It is a large crystal exhibiting such superconductivity, and according to the present invention, physical properties such as anisotropy of magnetic and electrical properties of an oxide can be strictly measured, and information on anisotropy can be obtained. It is important to clarify the conductivity and contribute to the research of the mechanism of superconductivity.

[Brief description of the drawings]

1 and 2 are explanatory views of an infrared concentrated heating furnace of a mono-ellipsoidal or bi-elliptic spheroidal mirror used for producing a superconducting oxide single crystal of the present invention, and FIG. 3 is an embodiment of the present invention. Structural photograph of the grown crystal of La _2-x Sr _x CuO ₄ (x = 0.15) in Example 1,
Fig. 4 is a measurement graph of the electric resistance-temperature characteristics of the grown crystal of La _2-x Sr _x CuO ₄ (x = 0.15), Fig. 5 is a photograph of the facet rear Laue crystal, and Fig. 6 is the grown La _0.186 Sr _0.14 Explanatory drawing of temperature change of electric resistance in the a-axis and c-axis directions of CuO ₄ crystal
FIG. 8 is a measurement graph of the Meissner effect in Example 2 of the present invention, FIG. 8 is a state diagram of the Nd ₂ O ₃ —CuO system, and FIG. 9 is (Nd, C
e) Phase diagram of ₂ O _{3 + δ-} CuO system, FIG. 10 is a structural photograph of a grown crystal of Nd _2−x Ce _x CuO ₄ in Example 3 of the present invention, and FIG. 11 is Meissner in Example 3 of the present invention. A measurement graph of the effect, FIG. 12 (a) is a schematic state diagram of decomposed and molten compound AB by the TSFZ method, FIG. 12 (b) is an explanatory view of the principle of the TSFZ method, and FIG. 13 is La ₂ O ₃ − in air. CuO system phase diagram, Figure 14 shows LaO _1.5
It is a CuO system phase diagram. In the figure, 1a: bi-elliptical rotating surface mirror, 2: infrared lamp, 3: solvent, 4: sintering raw material rod, 5: upper rotating shaft, 6: seed crystal, 7: lower rotating shaft, 8: transparent quartz tube, 9: lens, 10: screen, 11: atmospheric gas inlet, 12: atmospheric gas outlet.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location C30B 29/22 ZAA C30B 29/22 ZAA Patent Law Article 30 Clause 1 Application for application Journal of CRYSTAL GROWTH Vol. 96 No. 3 Published on p711-715 (1989-7) Judgment No. 6-17207 (56) Reference JP-A-63-230594 (JP, A) JP-A-63-274697 (JP, A) JP-A-1-179790 (JP, A) Proceedings of the 57th Autumn Meeting of the Chemical Society of Japan, page 232 (sho 63-9-6), Proc. Of the 33rd Symposium on Artificial Minerals, pages 71-72 (sho 63-9-24)

Claims (5)

(57) [Claims] 1. A tetragonal oxide exhibiting anisotropy and superconductivity, and a firing raw material rod having substantially the same stoichiometric composition as the superconducting oxide is treated under an oxygen pressure of 0.15 MPa or more. A crystal obtained by dissolving in a solvent mainly composed of copper oxide placed in an infrared concentrated heating furnace and depositing on a seed crystal, the crystal being a tetragonal system and the growth direction of the crystal. there is a shaft, and wherein the superconducting oxide is the _{Nd 2-x Ce x CuO 4} , YBa 2 Cu 3 O 7-x, BiSrCaCu 2 O x _{or, Tl 2 Ba 2 Ca 2 Cu} 3 O x A single crystal of a superconducting oxide characterized in that 2. The single crystal of superconducting oxide according to claim 1, wherein the single crystal has a diameter of 5 mm or more and a length of 40 mm or more. 3. The relative position between the seed crystal and the heating source is set in a state in which a solvent disposed between the raw material oxide and the seed crystal is heated and melted and is in contact with the raw material oxide and the seed crystal. A method for producing a single crystal of a superconducting oxide, which comprises moving an oxide having a tetragonal crystal structure on the seed crystal and a crystal growth direction of which is an a-axis in a controlled atmosphere. The stoichiometric composition of the raw material oxide is substantially the same as the superconducting oxide, the solvent is mainly copper oxide and the oxygen pressure of the atmosphere is 0.15 MPa or more, and the superconducting _{oxide, Nd 2-x Ce x CuO} 4, YBa 2 Cu 3 O 7-x, BiSrCaCu 2 O x , or the superconducting oxide, characterized in that the _{Tl 2 Ba 2 Ca 2 Cu 3} O x Method for producing single crystal. 4. The superconducting oxidation according to claim 3, wherein in growing the single crystal, the solvent composition is 55 to 91 mol% CuO, the growing temperature is 1100 to 1300 ° C., and the growing rate is 0.5 to 3 mm / h. Method for producing a single crystal of a product. 5. The method for producing a single crystal of superconducting oxide according to claim 4, wherein the single crystal is annealed in oxygen or nitrogen.