JPH0471877B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing a La ₂ CuO ₄ single crystal using a floating zone method.

[Conventional technology] La ₂ CuO ₄ single crystal has a small amount of Ba or Sr at the position of the La atom.
When replaced with atoms, it becomes a superconductor at low temperatures of 30 to 40 K, and is expected to find future applications as cryogenic devices. Therefore, large-sized, high-quality single crystals are desired, and the development of methods for producing them is desired.

However, as La ₂ CuO ₄ decomposes and melts at around 1050°C when heated to high temperatures, single crystals cannot be produced from raw materials with the same composition as single crystals. Therefore, crystal growth is carried out using the flux method or the solution pulling method. With the flux method, a single crystal with a maximum size of 8 x 8 x 2 mm can be produced in 3 days, while with the solution pulling method, a single crystal with a maximum size of 9 x 7 x 4 mm can be produced with a growth time of 9 to 10 hours.
To date, single crystals of the size have been grown.

[Problems to be Solved by the Invention] As described above, in the flux method, crystal growth takes a long time, the grown crystals are small, and an operation to separate the grown crystals from the flux is required. In addition, the solution pulling method requires fairly sophisticated crystal growth technology.
A very small amount of the starting material filled in the container becomes a single crystal, and most of it remains in the container, resulting in problems such as the need to throw away expensive raw materials because the purity decreases after several crystal growths.

[Means for Solving the Problems] In view of the above-mentioned circumstances, the present invention is based on the phase equilibrium diagram of the La ₂ O ₃ -Cu0 system and researched a floating zone method suitable for actual production of La ₂ CuO ₄ single crystals. As a result, 28.9 to 7.1 mol% of at least one of lanthanum oxide and lanthanum carbonate and 71.1 to 71.1 mol% of copper oxide are contained between the lanthanum cuprate raw material rod and the seed crystal.
A solvent consisting of 92.9 mol% is provided, and the solvent is 1040 ~
It is characterized by heating to 1330°C to form a floating molten zone, and by moving the floating molten zone in the direction of the raw material rod, a single crystal is precipitated and grown on the seed crystal.

Note that even if a small amount of some kind of foreign element is mixed in at the positions of the La and Cu atoms in La ₂ CuO ₄ , the phase equilibrium diagram is qualitatively the same as the phase equilibrium diagram of the La ₂ O ₃ −Cu0 system. In addition, by mixing a small amount of a different element into the raw material rod, it is also possible to produce a La ₂ CuO ₄ solid solution single crystal mixed with a different element by the same method.

[Operation] First, the principle of this invention will be described. Figure 1 was drawn from the results of differential thermal analysis and rapid cooling/heating method.
It is a phase equilibrium diagram of the La ₂ O ₃ −Cu0 system. In the figure, the black dots indicate the measurement results. For example, when La ₂ CuO ₄ having a composition of 50 mol % La ₂ O ₃ and 50 mol % Cu0 is heated, it decomposes and melts at around 1050°C.

Next, the composition ratio between liquidus line A-B, that is, La ₂
After heating and melting a raw material containing 28.9 to 7.1 mol% of _O3 and 71.1 to 92.9 mol% of Cu0 at approximately 1330 to 1040°C, when the temperature of the melt is gradually lowered, the composition of the melt changes to a liquid phase. It shifts toward the Cu0 side of the figure along the line A-B, and La ₂ CuO ₄ becomes a solid phase and precipitates. If the composition of the melt is closer to Cu0 than the eutectic point B,
Cu0 precipitates first during cooling, and if the composition of the melt is on the La ₂ O ₃ side from point A, crystals on the La ₂ O ₃ side precipitate first during cooling, and in both cases La ₂ CuO ₄ precipitates and grows. I can't.

In this invention, in the floating zone method, the composition of the solvent provided between the La ₂ CuO ₄ raw material rod and the seed crystal is such that at least one of lanthanum oxide and lanthanum carbonate is 28.9 to 7.1 mol%;
Copper oxide is 71.1~92.9 mol%, solvent is 1050~
Melt by heating to 1350°C, move in the direction of the raw material rod while keeping the above melt composition stable, and add La ₂ to the seed crystal.
It grows CuO ₄ single crystals.

[Examples] The present invention will be explained in detail below using Examples.

Example 1 A La ₂ CuO ₄ single crystal was produced by the floating zone method.

Figure 2 shows the floating zone single crystal manufacturing apparatus used. In the figure, 1 is a raw material rod, 2 is a seed crystal, 3 is a melting zone (solvent), 4 and 5 are rotating shafts, 6 is a quartz tube, 7 is a halogen lamp, 8 is a spheroidal mirror, 9 is a monitoring window, 10 is a lens, and 11 is a monitoring screen.

A powder made by mixing La ₂ O ₃ and Cu0 in a molar ratio of 1:1 was fired at 900℃ for 2 hours, and the powder was molded into a round bar with a diameter of 6 mm and a length of 7 cm using a pressure molder at 950℃.
The mixture was fired homogeneously for 2 hours to obtain La ₂ CuO ₄ raw material rod 1.

Similarly, after baking a powder of 15 mol% La ₂ O ₃ and 85 mol% Cu0 at 900°C for 2 hours,
The product was pressure-molded into a round bar shape with a diameter of 6 mm, and baked homogeneously at 950°C for 2 hours to use as a solvent. Thereafter, this cylindrical rod-shaped solvent is cut in the radial direction to form a disk weighing 0.5 to 0.9 g and fused to the La ₂ CuO ₄ raw material rod.

In this way, the cylindrical rod-shaped sample with the solvent fused to the tip of the La ₂ CuO ₄ raw material rod was fixed to the upper sample rotation shaft 4 of the floating zone method single crystal manufacturing apparatus that adopted the infrared heating method, and the lower rotation shaft was similarly fixed. Seed crystal 2 is fixed on shaft 5. In this case, the seed crystal 2 and the La ₂ CuO ₄ raw material rod 1 coated with the solvent are set so as not to be eccentric with respect to the rotation axis. After the solvent is heated and melted using infrared rays using a halogen lamp 7, the seed crystal is brought into contact with the solvent, and the solvent is held between the raw material rod and the seed crystal by the surface tension of the liquid.

Thereafter, the raw material rod and the seed crystal are rotated at 30 rpm in opposite directions.

Further, this melted solvent is moved toward the raw material rod, that is, upward, at a rate of 1 to 2 mm/hr, to grow a La ₂ CuO ₄ single crystal as a seed crystal. It should be noted that even if this growth was carried out under atmospheric pressure and 1 atm of oxygen, the transpiration of Cu0 etc. was very small and there was no problem.

When the raw material rod was almost consumed, the grown single crystal and the raw material rod were separated and cooled to room temperature. As a result, a cylindrical rod-shaped La ₂ CuO ₄ single crystal with a diameter of 5 mm and a length of 5 mm was obtained.

Example 2 A solid solution single crystal having the composition (La _0.9 Ba _0.1 ) ₂ Cu0 ₄ was produced by the floating zone method.

The molar ratio of a mixture of 90 mol% La ₂ O ₃ + 10 mol% 2BaCO ₃ and Cu0 is 1:1 and 15:85.
Using the mixed powder as a raw material rod and a solvent, the same procedure as in Example 1 was carried out to obtain a (La _0.9 Ba _0.1 ) ₂ Cu0 ₄ solid solution single crystal with a diameter of 5 mm and a length of 8 mm.

In the production method of this invention, even if the position of the La atom in the crystal is replaced with Ba, the phase equilibrium diagram of the La ₂ O ₃ -Cu0 system shown in Figure 1 remains essentially unchanged (La _0.9 Ba _0.1 ) ₂
A Cu0 ₄ single crystal was produced.

Even if a small amount of a different element is mixed at the Cu position, if the above phase equilibrium diagram does not essentially change qualitatively, a La ₂ CuO ₄ solid solution single crystal mixed with a different element can be obtained in the same way. .

When producing a La ₂ CuO ₄ single crystal, lanthanum carbonate (La ₂ (CO ₃ ) ₃ ) was used instead of lanthanum oxide (La ₂ O ₃ ).
can also be used as a starting material. La ₂
(CO ₃ ) ₃ undergoes the following reaction during heating: La ₂ (CO ₃ ) ₃ →La ₂ O ₃ +3CO ₂ ↑ and changes to La ₂ O ₃ . Therefore, even if La ₂ (CO ₃ ) ₃ and Cu0 are used as starting materials, a phase equilibrium diagram completely similar to that shown in FIG. 1 is obtained as a result, and La ₂ CuO ₄ single crystals and single crystals in which part of La was replaced with Ba or Sr were obtained.

[Effects of the Invention] As explained above, according to the present invention, a high-quality La ₂ CuO ₄ single crystal can be produced in any crystal axis direction in a relatively short time. Moreover, since most of the raw materials used for production can be made into single crystals, raw material costs can be saved compared to the flux method and the solution pulling method.

[Brief explanation of the drawing]

Figure 1 is La ₂ for explaining the principle of this invention.
The phase equilibrium diagram of the O ₃ -Cu0 system, and FIG. 2 is a cross-sectional view of the floating zone single crystal manufacturing apparatus. 1... Raw material rod, 2... Seed crystal, 3... Melting zone, 7... Halogen lamp.

Claims (1)

[Claims] 1 Between the lanthanum cuprate raw material rod and the seed crystal, at least one of lanthanum oxide and lanthanum carbonate is present in an amount of 28.9 to 7.1 mol%, and copper oxide is present in an amount of 71.1 to 92.9 mol%.
A single crystal is precipitated and grown on the seed crystal by providing a solvent consisting of, heating the solvent to 1040 to 1330°C to form a floating molten zone, and moving the floating molten zone in the direction of the raw material rod. Characteristic manufacturing method of lanthanum cuprate single crystal. 2. The method for producing a lanthanum cuprate single crystal according to claim 1, wherein the raw material rod contains a small amount of a different element.