JPH01179790A - Production of single crystal of high temperature superconductor - Google Patents

Abstract

PURPOSE:To obtain a large single crystal having uniform compsn. and uniform crystal orientation by controlling a compsn. of component elements in a melting zone when a single crystal of a high temp. superconductor consisting of a rare earth element an alkaline earth element-Cu is produced by a floating zone method. CONSTITUTION:A single crystal (4) is grown from a melting zone (5) in a mixed gas atmosphere consisting of O2 and inert gas by combining vertically a rod- shaped sintered body (3) having a same compsn. as a compsn. of elements of a single crystal (4) to be produced with a rod-shaped sintered body (5) having a same compsn. as a compsn. of elements of the melting zone which coexists in equilibrium with the single crystal (4) to be produced. It is preferred that the compsn. of said rod-shaped sintered body (3) is R1A2Cu3O7-x, and that the compsn. of said rod-shaped sintered body (5) is R1A2.7-yCu4-zO8.7-w wherein each R and A is a rare earth element and an alkaline earth element, respectively; 0<=x<=0.5; -0.5<=y<=0.5; -0.8<=z<=0.8; -1.0<=w<=1.0.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method for producing a high temperature superconductor single crystal.

(Prior art and its problems) High-temperature superconducting materials having an oxygen-deficient layered perovskite structure consisting of rare earth element-alkaline earth element-copper oxides represented by the Y-Ba-Cu-0 system are It is expected to be applied to a wide range of applications in institutions, heavy electrical equipment, computers, and medical equipment.

These oxide-based high-temperature superconducting materials also become superconducting when cooled with an inexpensive coolant such as liquid nitrogen, so Nb, which only exhibits a superconducting state in liquid helium,
-If it can be used in superconducting magnets instead of Ti-based superconducting alloys, there will be great economic advantages.

However, the critical current density of the oxide-based superconducting materials that have been produced so far is as low as several + A/afl, which is 1/200 to 1/4 of the Nb-Ti-based superconducting alloys conventionally used for boat fishing.
There was a drawback that it was only 00.

Another problem was that the temperature range of the transition from normal conductivity to superconductivity was wide and lacked steepness.

It has been pointed out that one of the causes of these problems is that oxide-based superconducting materials are porous and have a low density.

Up until now, methods for manufacturing large single crystals of superconducting materials have been studied in an attempt to solve the above problems, but because the oxides of each component element melt at different temperatures, it is difficult to achieve a uniform crystal type and elemental composition. It was difficult to grow crystals.

Furthermore, due to the phase transition that occurs during crystal cooling, many twin grain boundaries occur, making it difficult to obtain large single crystals of good quality.

In fact, a method for producing large, high-quality single crystals is desired not only for the application of oxide-based superconducting materials to devices, but also for elucidating the mechanism by which superconducting states occur through structural analysis and physical property measurements.

(Technical means for solving the problem) As a result of intensive research to solve the above problem, the present inventors found that when producing crystals by the floating zone method, the constituent elements of the molten zone We have found that by controlling the composition, large single crystals with more uniform composition and crystal orientation can be obtained.

The present invention provides a method for producing a high-temperature superconductor single crystal consisting of rare earth element-alkaline earth element-copper oxides by a floating zone method, using a sintered offering having the same elemental composition as the single crystal to be produced. A compact (hereinafter referred to as a sintered compact A) and a sintered compact (hereinafter referred to as a sintered compact B) having the same elemental composition as the molten zone that coexists in equilibrium with the single crystal to be manufactured are placed one above the other. This is a method for producing a high-temperature superconductor single crystal, characterized in that the single crystal is grown from a molten zone in a mixed gas atmosphere of oxygen and an inert gas.

The sintered sintered body A used in the present invention can be manufactured by a generally well-known method. That is, R+AzCuiOt-
x (R and A represent rare earth elements and alkaline earth elements, respectively, and 0.≦−X≦0.5.) Salt powder, etc. is crushed and mixed with a ball mill, crusher, pestle, mortar, etc., the mixed powder is temporarily sintered, and then the powder is pressure-formed into a rod shape with a rubber press, etc.
A sintered body A is obtained by sintering. The raw material powder for pressure molding can also be obtained by pre-sintering a coprecipitate formed by contacting a solution of constituent element compounds according to the composition of the single crystal produced in the present invention with a precipitate forming agent. It will be done.

The sintered sintered body A may have any shape and dimensions, and can be used as, for example, a 15xl 5x100 mm square column, or a cylinder with a diameter of 15 mm and a length of 150 mm.

The sintered sintered body B used in the present invention can be produced in the same manner as the sintered sintered body A, except that the quantitative ratio of the constituent element compounds used is different.

The quantitative ratio of the constituent element compounds of the offering-shaped sintered body B can be determined by the following method.

In a mixed gas atmosphere of oxygen and inert gas, a mixture of rare earth elements, alkaline earth elements, and copper oxides is heated and held, then rapidly cooled, and the quenched product is turned into a powder to identify the crystal phase and composition. By performing the analysis, it is possible to know the composition of the surface phase and liquid phase that coexist during heating. Therefore, by changing the oxygen partial pressure in an inert gas atmosphere, the composition of the mixture of rare earth elements, alkaline earth elements, and copper oxide, and the heating and holding temperature, the solid phase and liquid phase coexisting during heating can be Once the composition is known, the single crystal produced by the present invention (RIA tCuzO
The composition of the melting zone where 7-x) crystallizes can be determined.

As a method of combining a plurality of sintered sintered bodies having different compositions used in the floating zone method of the present invention, (1) sintered sintered bodies A and sintered sintered bodies B are placed in the vertical direction. There are methods such as overlapping, or (2) sandwiching the sintered sintered body B between two sintered sintered bodies A.

An example of the floating zone method according to the present invention will be explained based on a conceptual diagram of the apparatus for the case where the combination of the above-mentioned sintered bodies is (2).

In FIG. 1, a high frequency coil 7 generates high frequency waves to inductively heat a heating ring 6, and the heat melts a sintered body B to form a molten zone 5. The sintered sintered body A3 held in the holder 2 is slowly moved downward while controlling the melting of the sintered body A3 at the lower end of the melting zone and the precipitation of the rod-shaped single crystal 4 at the lower end of the molten zone. The moving speed of the holder 2 is preferably 1 to 10 mm/hour.

The mixed gas atmosphere of oxygen and inert gas in the present invention is an inert gas mixture containing oxygen at a volume fraction of 0.1 to 50%, and examples of the inert gas include helium, argon, neon, nitrogen, and their like. Examples include mixtures. The inert gas mixture containing oxygen is used primarily to suppress the evaporation of the material and the wear and tear of the heating ring 6. The total pressure of the mixed gas atmosphere of oxygen and inert gas is 0
．． The pressure is 1 to 100 atm, preferably 0.5 to 50 atm. A pressure lower than 0.1 atm has little effect on suppressing evaporation and consumption, and a pressure higher than 100 atm is undesirable because heat loss due to convection or the like increases.

When growing a single crystal, the upper and lower shafts 1 are rotated to mix and stir the molten zone, thereby facilitating the growth of the single crystal.

(Example) Examples of the present invention are shown below.

Example 1 Powders of Y2O3, B a CO3 and CuO were mixed into Y:Ba
:cu- After mixing at an atomic ratio of 1:2:3, it was formed into two cylinders with a diameter of 15 mm and a length of 150 sn with 50 dishes using a rubber press, and this was sintered at 900"C in the air for 4 hours. A sintered body A having a composition of Y, BazC11s06.s was obtained.

Next, YlBaz and 7 cu.
4. +on, a sintered body B having a composition of 7 was obtained.

The two sintered sintered bodies A mentioned above were supported by a holder (2 in FIG. 1), and the sintered sintered body B was sandwiched between them.

In a helium mixed gas atmosphere with a total pressure of 5 atm and an oxygen partial pressure of 0.5 atm, the sandwiched molten zone-forming sintered body B is melted to form a molten zone, and the upper and lower sintered sintered bodies are sintered. body A 3
It was moved downward at a cylinder/hour and rotated at 1 Orpm. As a result, the upper sintered body A melted into the molten zone, and crystals of Y+BazCu30i,s composition were grown in the lower part of the molten zone. In order to check the quality of the obtained crystal rod with a diameter of 12 mm and a length of 25 mm, the rocking curve of the ζ (100) plane was measured using a double crystal diffractometer, and the half width of the diffraction curve was 0. 1°, and this crystal rod was found to be a large, high-quality single crystal composed of single crystal grains and with a very low proportion of twin grain boundaries.

When annealing was performed at 550°C for 2 days in an oxygen atmosphere of 1 atm and AC magnetic susceptibility was measured, a clear Meissner effect was shown. The superconducting transition temperature from electrical resistance determined by the DC four-probe method was 93.

Example 2 The composition of the sintered sintered body A is La, BazCu, O,,s, and the composition of the sintered sintered body B forming the molten zone is La.

B a , 2Cu, 0.0. The same method as in Example 1 was repeated except that the atmosphere was changed to argon mixed gas with a total pressure of 20 atm and an oxygen partial pressure of 0.3 atm.

(1
The half width from the rocking curve of the 00) surface is 0.06°
This crystal rod is composed of a single crystal grain, and is a large, high-quality LaJa2Cu with a very low proportion of twin grain boundaries.
s06. It turned out to be a single crystal.

The superconducting transition temperature from electrical resistance using the DC 4-terminal method is 3
It was on 2nd.

Example 3 The composition of the sintered sintered body A is Er+BazCusO6,q, and the composition of the sintered sintered body B forming the molten zone is Er+B a i
, zc u:+, zos, o, and an argon mixed gas atmosphere with a total pressure of 0.5 atm and an oxygen partial pressure of 0.3 atm, but the same method as in Example 1 was repeated.

The obtained crystal rod with a diameter of 11.5 mm and a length of 30 mm (
The half width from the rocking curve of the 100) surface is 0.13
°, and this crystal rod is composed of a single crystal grain, and is a large, high-quality E r +B with a very low proportion of twin grain boundaries.
It was found to be azCu30b,q single crystal.

The superconducting transition temperature from electrical resistance using the DC 4-terminal method is 9
It was on 5th.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram showing the production of a single crystal by the floating zone method. '1 is a shaft, 2 is a holder, 3 is a sintered body A, 4 is a rod-shaped single crystal, 5 is a molten zone (sintered body B), 6 is a heating ring, and 7 is a high-frequency induction heating coil. It is.

Claims (2)

[Claims] (1) When producing a high-temperature superconductor single crystal consisting of a rare earth element-alkaline earth element-copper oxide by the floating zone method, a rod-shaped sintered body having the same elemental composition as the single crystal to be produced is produced. and a rod-shaped sintered body having the same elemental composition as the molten zone that coexists in equilibrium with the single crystal to be produced are vertically assembled, and the single crystal is extracted from the molten zone in a mixed gas atmosphere of oxygen and inert gas. A method for producing a high-temperature superconductor single crystal characterized by growing it. (2) A rod-shaped sintered body whose composition is R_1A_2Cu_3O_7_-_x, which has the same elemental composition as the single crystal to be manufactured, and the same elemental composition as the molten zone that coexists in equilibrium with the single crystal to be manufactured. Body composition is R_1A_2_. ＿7＿−＿yCu_4＿−＿zO_8
＿． _7_-_w The manufacturing method according to claim (1). In both formulas above, R and A represent rare earth elements and alkaline earth elements, respectively, and 0≦x≦0.5, -0.5
≦y≦0.5, -0.8≦z≦0.8, -1.0≦w≦
It is 1.0.