JPH0471875B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing copper lanthanum (La ₂ CuO ₄ ) single crystal by a flux method.

[Prior art] La ₂ CuO ₄ is an oxide with a layered perovskite structure, which exhibits superconductivity at low temperatures by replacing a small amount of La atoms with Ba or Sr atoms, and its transition temperature is as high as 30 to 40 k. , future applications as cryogenic devices are possible. Therefore, large-sized, high-quality single crystals are desired, and the development of methods for producing them is desired.

Although photographs of conventionally grown crystals of approximately 5 x 5 x 1 mm in size have been published, the details of the manufacturing method have not been made public at all.

[Problems to be solved by the invention] For crystal growth in the flux method, it is necessary to clarify the flux that precipitates the desired single crystal, its composition range, and crystal growth temperature range. is required.

[Means for Solving the Problems] In order to solve the above problems, the present invention includes the following:
A phase equilibrium diagram of the La ₂ O ₃ -CuO system is created, and a La ₂ CuO ₄ single crystal is grown using it as a guideline. The present invention contains 28.9 to 7.1 mol% of at least one of lanthanum oxide and lanthanum carbonate and 71.1 mol% of copper oxide.
After mixing at ~92.9 mol% and heating and melting at 1040-1330°C, the melt is slowly cooled to precipitate microcrystals represented by the general formula La ₂ CuO ₄ , and the microcrystals are crystallized in the melt. It is characterized by being cultivated.

[Effect] Perform differential thermal analysis and rapid cooling heating method, and test the sample with
From the results of line diffraction, we found that La ₂ O ₃ −CuO shown in Figure 1
A phase equilibrium diagram of the system was created. In the figure, the black dots indicate the measurement results.

From Figure 1, the La ₂ CuO ₄ single crystal has a composition ratio of liquidus line AB, that is, La ₂ O ₃ is 28.9 to 7.1 mol%, CuO is 71.1 to 7.1 mol%.
From a melt with a composition in the range of 92.9 mol%, approximately 1330 ~
It is thought that it precipitates in the temperature range of 1040℃. That is, when a melt having the above-mentioned composition is slowly cooled, the composition of the melt shifts toward the CuO side along the liquidus line AB, and La ₂ CuO ₄ becomes a solid phase, precipitates, and grows as it cools.

If the composition of the melt is closer to CuO than the eutectic point B, CuO will precipitate first during cooling, and the composition of the melt will be closer to the CuO point than the eutectic point B.
If it is on the La ₂ O ₃ side, crystals on the La ₂ O ₃ side precipitate first during cooling, and La ₂ CuO ₄ cannot precipitate and grow in either case.

Furthermore, even if a small amount of some kind of foreign element is mixed into the La ₂ CuO ₄ single crystal La atom or Cu atom position, the phase equilibrium diagram will qualitatively be the same as the phase equilibrium diagram of the La ₂ O ₃ -CuO system in Figure 1. _If there is essentially no difference _between be. for example,
It is possible to produce a La ₂ CuO ₄ solid solution single crystal containing a small amount of different elements such as Sr and Ba.

[Example] Next, embodiments of this invention will be described.

Example 1 A La ₂ CuO ₄ single crystal was produced by a flux method.

Mix La ₂ O ₃ and CuO in a molar ratio of 20:80,
Put 100g of the mixture into a platinum crucible with a diameter of 50 mm and a height of 40 mm, cover with an alumina lid, put the crucible into an alumina crucible with a lid, and then put it into a fireproof box with a lid. sealed in.
The mixture was placed in a Matsufuru furnace and heated to about 1350°C for 2 hours, then the temperature was lowered to 1050°C at a rate of about 8°C/h, and then to room temperature at a rate of 200°C/h. As a result, from the solidified flux a piece of 8 x 8 x 2 mm was found.
A La ₂ CuO ₄ single crystal was obtained.

Example 2 A solid solution single crystal having the composition (La _0.9 Ba _0.1 ) ₂ CuO ₄ was produced by a flux method.

A mixture with a composition of 90 mol% La ₂ O ₃ + 10 mol% 2BaCO ₃ and CuO were mixed at a molar ratio of 20:80, and a mixture of 8×
A (La _0.9 Ba _0.1 ) ₂ CuO ₄ solid solution single crystal of 8×1 mm was obtained.

Example 3 A solid solution single crystal having the composition (La _0.9 Sr _0.1 ) ₂ CuO ₄ was produced by a flux method.

A mixture with a composition of 90 mol% La ₂ O ₃ + 10 mol% 2SrCO ₃ and CuO were mixed at a molar ratio of 20:80, and a mixture of 2×
A (La _0.9 Sr _0.1 ) ₂ CuO ₄ solid solution single crystal of 4×0.5 mm was obtained.

In addition, in Examples 2 and 3, the La atom position was replaced with a small amount of a different element (Ba or Sr),
This is because the phase equilibrium diagram qualitatively shows La ₂ O ₃ −CuO in Figure 1.
It was shown that it is possible to produce a La ₂ CuO ₄ solid solution single crystal containing a different element by mixing a small amount of the different element into the solution if it is essentially the same as the phase equilibrium diagram of the system. There is. Similarly to this
Even if a small amount of a different element is mixed in the position of Cu, 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 CuO are used as starting materials, a phase equilibrium diagram exactly the same as 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.

[Effect of the invention] As explained above, according to this invention, La ₂ CuO ₄
Single crystals can be produced by the flux method. Furthermore, a single crystal containing a small amount of Ba and Sr can be produced. Thus, according to the present invention, it has become possible to produce an oxide superconducting single crystal exhibiting superconductivity at 30 to 40 k.

[Brief explanation of the drawing]

FIG. 1 is a phase equilibrium diagram of the La ₂ O ₃ --CuO system created by the inventor of the present application.

Claims (1)

[Claims] 1. 28.9 to 7.1 mol% of at least one of lanthanum oxide and lanthanum carbonate, and 71.1 to 7.1 mol% of copper oxide.
After mixing at 92.9 mol% and heating and melting at 1040 to 1330°C, the melt is slowly cooled to obtain the general formula
1. A method for producing a copper lanthanum single crystal, which comprises precipitating microcrystals represented by La ₂ CuO ₄ and growing the microcrystals in a melt. 2. The method for producing a copper lanthanum single crystal according to claim 1, wherein the copper lanthanum contains a small amount of a different element.