JPH0818909B2 - Oxide superconductor single crystal growth method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a method for growing an oxide superconductor that can be used in a photodetector or the like using a Josephson junction.

[Conventional technology]

La ₂ CuO ₄ is a semiconductor, but it has been reported by Michel et al. That a part of La is replaced with Ca, Sr, Ba, etc. to change to metal conduction (Michel, C., Raveau, B .; Chem. Min. 21,407
(1984)). More recently, Bednorz et al.
It was shown that it is a superconducting material of C (x = 0.075 at M = Ba, 30K, Sr at x = 0.1, 40K or more). This Tc is currently being updated.

[Problems to be solved by the invention]

Until now, such high Tc materials have been used in ceramic samples, but single crystals are necessary to know the exact physical properties of materials. In particular, this material has a layer of CuO ₆ octahedra arranged two-dimensionally as shown in Fig. 1 and a NaCl-type (La _1-x M _x ) ₂ O ₃
Due to the structure in which (M = Ca, Sr, Ba) layers are alternately arranged, the electrical characteristics have a large anisotropy in the direction parallel to the CuO ₆ octahedron layer and in the direction perpendicular thereto, but In the sample, only the characteristics obtained by averaging each direction are obtained. In addition, a Josephson junction was formed at the polycrystalline grain boundary, but the characteristics were determined by the grain size, etc., and controllability was poor.

[Means for Solving Problems] High-Temperature Superconductor (La _1-x M _x ) ₂ Cu _1-y Ni _y O ₄ (M = Ca, Sr, B
a, x = 0-1, y = 0-0.05) "is an oxide superconductor (La _1-x M
_x ) ₂ CuO ₄ and (M = Ca, Sr, Ba, 0 <x <1) single crystal is grown by a precipitation method.

CuO or KF is used as the solvent. Of these, CuO is 1024
It is a substance that melts at temperatures above ℃. (La _1-x M _x ) CuO ₄
When Cu is added to CuO and heated, the whole is melted when a certain temperature determined by the solubility in CuO determined by M, x and the content of (La _1-x M _x ) CuO ₄ is reached. Actually a few more than this temperature
Heat to a high temperature of 10 ℃ and dissolve completely until the fine crystals disappear.

After the entire material is completely melted, if it is slowly cooled this time, the solubility will be determined by the composition, so crystals will start to precipitate when the temperature reaches the saturated solubility (depending on the packing material) or lower. KF is a substance that dissolves at 858 ° C., and even when KF is used as a solvent, a single crystal can be deposited by the same procedure.

〔Example〕

[Example 1] La ₂ O ₃ , SrCO ₃ , and CuO powder were previously used (La _0.9 S
r _0.1 ) ₂ CuO ₄ is synthesized. CuO 60g (La _0.9 Sr
_0.1 ) ₂ CuO ₄ 100g (20mol%) in a platinum crucible (50cmφ × 5
(0 cm) and heated to 1300 ℃ in an electric furnace, the whole melts. Hold in this state for several hours. After that, the upper part of the solution was cooled to a few degrees Celsius lower than the bottom, and was gradually cooled at 3.3 ° C / hr while maintaining the same temperature difference.

Around 1140 ° C, a square plate-like crystal with a thickness of around 1 mm and a side of 5 to 10 mm precipitates. The crystals have a specific gravity smaller than that of CuO, so a few crystals appear floating on the surface, but they can be scooped up using a platinum net.

A part of the crystal was crushed into a powder and the X-ray diffraction was measured, as shown in FIG. Composition analysis by fluorescent X-ray shows that Sr in crystals
Content is half of the composition of the raw material (La _0.95 Sr _0.05 ) ₂ CuO ₄
Had a composition close to. FIG. 3 shows the electric resistance of this crystal in the direction parallel to CuO ₆ . The resistance gradually decreases from 110K and drops sharply from 7K. The resistance becomes completely zero at 4K.

Example 2 (La _0.8 Sr _0.2 ) ₂ CuO ₄ was synthesized and used as a raw material. C
When 20 mol% of this raw material was added to uO and heated in a platinum crucible of the same volume as in Example 1, the whole melted at 1350 ° C. When gradually cooled at 3.3 ° C./hr, a single crystal having a size almost the same as in Example 1 was obtained at around 1180 ° C.

The composition of the crystal is close to (La _0.9 Sr _0.1 ) ₂ CuO ₄ and Tc is the third
It was 40K as shown in FIG.

[Example 3] (La _0.8 Ba _0.2 ) ₂ CuO ₄ was used as a raw material, and was 20 mol% with respect to CuO.
If added to obtain crystals of the composition of _{(La 0.95 Ba 0.05) 2 CuO} 4, Tc was 30K.

In the case of M = Sr, Ba, for x = 0 <x <1, a single crystal having a thickness of about 1 mm and a side of several mm can be easily obtained by the above method.

 The same applies when M is Ca.

In the above example, the method of scooping up the single crystal precipitated in the solution was adopted, but the seed crystal having the same composition as the precipitated crystal was held at the tip of the rod in the region where the single crystal was being precipitated, and the seed crystal was immersed while rotating from above. If so, a single crystal having a certain directionality grows from the tip of the seed crystal, and by pulling this, a larger single crystal can be obtained.

In addition, in the above-mentioned embodiment, a part of Cu of (La _1-x M _x ) ₂ CuO ₄ can be replaced with Ni. This replacement is possible in (La _1-x M _x ) ₂ Cu _1-y Ni _y O ₄ in the range of 0 <y <0.05. Superconductivity is maintained within this range.

When the solvent is KF, the whole can be dissolved by heating to about 950 ° C. Since the oxide that precipitates due to the decrease in temperature has a higher specific gravity than the solvent, it precipitates at the bottom of the solvent. Therefore, it is effective to lower the temperature of the container holding the solvent at the bottom.

〔The invention's effect〕

As described above, according to the present invention, an oxide superconductor composed of a single crystal having a desired composition can be obtained, and thus it can be used as an electrode material or the like by utilizing its superconductivity. Moreover, a desired Josephson junction can be formed by ion implantation or the like, which is useful for producing a highly sensitive photodetector or the like.

[Brief description of drawings]

FIG. 1 is the crystal structure of (La _1-x M _x ) ₂ CuO ₄ , FIG. 2 is the X-ray diffraction pattern of the single crystal obtained in Example 1, and FIG. 3 is the results in Examples 1 and 2. The temperature change of the specific resistance of the obtained single crystal. 1 …… CuO ₆ octahedral layer arrangement, 2 …… (La _1-x M _x ) ₂ O
Arrangement of _3-x (NaCl type) layers, 3 ... Electric resistance of single crystal obtained in Example 1, 4 ... Electric resistance of single crystal obtained in Example 2.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Yoichi Enomoto Yoichi Enomoto Tokai-mura, Ibaraki Prefecture, Tokai-mura, Shirahoji 162 Shirane, Nippon Telegraph and Telephone Corporation Ibaraki Telecommunications Research Institute (72) Inventor Minoru Naka, Ibaraki Prefecture Tokai-mura Large-scale Shirokata 162 Shirane Shiba, Nippon Telegraph and Telephone Corporation Ibaraki Telecommunications Research Laboratories (72) Inventor Oda Ken Tokai-mura Large-scale Shirahane Shirane 162 Nippon Telegraph and Telephone Corporation Ibaraki Telecom (72) Inventor Kazuyuki Moriwaki 162 Shirahane, Shikatakata, Tokai-mura, Naka-gun, Ibaraki Prefecture Nippon Telegraph and Telephone Corporation Ibaraki Telecommunications Research Institute

Claims (1)

[Claims] 1. A solution of KF or CuO containing (La _1-x M _x ) ₂ CuO ₄ ,
(M = Ca, Sr, Ba; 0 <x <1) is dissolved, and the solution is gradually cooled to precipitate a single crystal of the substance. .