JP2697334B2 - Method for producing oxide superconductor single crystal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an oxide superconductor single crystal used for various superconducting applied devices and superconducting elements.

[0002]

2. Description of the Related Art Metal / alloy superconducting materials and compound superconducting materials have already been widely used as wires for Josephson devices and superconducting magnets. Josephson junctions have been applied to precision measurement such as SQUIDs due to their high sensitivity to magnetic fields, and are expected to be applied to electronic computers due to their high speed. Also, superconducting magnets that can generate high magnetic fields that cannot be obtained with ordinary conductors
It is also applied to medical equipment such as NMR-CT and floating linear motor cars.

In consideration of the application of superconductors, it is desired that the superconducting transition temperature Tc be as high as possible. Metal-alloy superconductors and compound superconductors require the use of expensive and rare liquid helium as a refrigerant, which is a factor that hinders the application of these superconductors to a wide range of fields. ing. In this regard, copper oxide-based superconductors are far superior to conventional superconductors, and in 1987 Ba-Y
-Since the discovery of Cu-O-based superconductors, Bi-Sr-
Superconductors having a Tc exceeding liquid nitrogen temperature, such as Ca-Cu-O and Tl-Ba-Ca-Cu-O, have been discovered one after another. If these oxide superconductors are put to practical use, the possibility of their application will be extended to fields that have never been considered before, and research and development are being actively conducted at present.

[0004]

Most of the currently studied oxide superconductor samples are polycrystalline. In a polycrystalline sample of a superconductor, it is difficult to form a Josephson junction having desired characteristics with good controllability because countless superconducting weak bonds exist at the crystal grain boundaries. In addition, since various defects and inhomogeneities contained in the polycrystal may adversely affect the stability of superconductivity, it is preferable to use a single crystal for application to devices and the like.

As one of methods for obtaining a Tl-based superconductor single crystal, there is a method using a KCl / NaCl or PbCl ₂ flux. These fluxes have the advantage that the crystals formed can be easily taken out because of their water solubility, but at the same time, the vapor pressure is high in the temperature range of about 900 ° C. where the crystals grow, so that they evaporate rapidly during the growth. Problem.

Accordingly, an object of the present invention is to provide KCl / NaCl
Another object of the present invention is to provide a method for suppressing the evaporation of the flux during the production of a Tl-based superconductor single crystal using a PbCl ₂ flux or PbCl ₂ flux.

[0007]

Means for Solving the Problems] To achieve the above object, in a method of manufacturing an oxide superconducting single crystal according to the present _{invention, Tl 2 Ba 2 Ca n-} 1 Cu n O 4 + 2n (n = 1,2,
The oxide superconductor single crystal represented by 3) was converted to KCl or K
In a manufacturing method using Cl + NaCl or PbCl ₂ as a flux, boron oxide (B ₂ O ₃ ) is added to a mixed powder forming an oxide superconductor material.

[0008]

DETAILED DESCRIPTION OF THE INVENTION The present _{invention, Tl 2 Ba 2 Ca n-} 1 Cu n O 4 + 2n to K
By adding B ₂ O ₃ in the synthesis Cl or KCl + NaCl or PbCl ₂ flux, the amount of evaporation flux pressed, good quality _{Tl 2 Ba 2 Ca n-1} Cu n O
It has been found that a _{4 + 2n} single crystal can be obtained. Based on this principle, Tl ₂ Ba ₂ CuO ₆ +20 KCl + 5
A single crystal produced from a mixed powder of B ₂ O ₃ composition at a maximum temperature of 920 ° C. and a slow cooling rate of 5 ° C./hour has a thickness of several mm square and a thickness of 0.1 mm.
It was about 1 mm in size and transitioned to superconductivity at 85K. Even though the temperature range from 920 ° C. to 850 ° C. where the amount of evaporation of KCl alone was particularly large was gradually cooled over 10 hours or more, actual KCl evaporation hardly occurred.

[0009]

EXAMPLES The present invention will be specifically described below with reference to examples.

(Example 1) Purity 99.9 as a starting material
% Thallium oxide (Tl ₂ O ₃ ), barium oxide (B
aO), calcium oxide (CaO), cupric oxide (Cu
O) was used. These raw materials _{Tl 2 Ba 2 Ca n-1} C
u _n O 4 _{+ 2n} were mixed at the ratio of, after pressing, and 3-5 hours sintered at 860 ° C. to 900 ° C. wrapped in gold foil.
The resulting pulverized sintered body _{Tl 2 Ba 2 Ca n-1} Cu n O 4 + 2n
In the general formula of +10 (KCl + NaCl) + xB ₂ O ₃ , n and x were mixed so as to have a compounding ratio shown in Table 1. After melting the mixed powder in a gold crucible having a diameter of 20 mm and a depth of 25 mm at 700 ° C. to 900 ° C. for 1 to 10 hours,
It was gradually cooled to 600 ° C. at a rate of 10 ° C. or less per hour. 60
It was cooled at a rate of 100 ° C. for 1 hour from 0 ° C. to room temperature.
Single crystal samples were removed by rinsing KCl, NaCl and B ₂ O ₃ with water.

[0011]

[Table 1]

[0012] A (Example 2) The same reagent as in Example 1 as a starting material to synthesize the _{Tl 2 Ba 2 Ca n-1} Cu n O 4 + 2n sintered body. The resulting pulverized sintered body _{Tl 2 Ba 2 Ca n-1} Cu n O
_{4 + 2n + 20PbCl 2 + xB} 2 O 3 becomes n in the general formula, for x were mixed so that the compounding ratio shown in Table 2. Melting, solidification, and removal of the single crystal were performed under the same conditions as in Example 1.

The obtained single crystal was measured for resistivity and diamagnetic susceptibility, and analyzed for composition. The resistivity was measured by a four-terminal method using a gold wire as a lead, and the diamagnetic susceptibility was measured by a SQUID magnetometer. Composition analysis was performed using EPMA.

[0014]

[Table 2]

Tables 1 and 2 show typical sizes and Tc of the obtained single crystals. If the amount of B ₂ O ₂ is too small, the effect of suppressing evaporation is not so large, and it is difficult to grow a single crystal at a temperature of 900 ° C. or more. On the other hand, if the amount of B ₂ O ₃ is too large, the amount of raw materials and the amount of flux charged are reduced, so that it is not practical.

[0016]

According to the production method of the present invention, it is possible to obtain a high-quality single crystals of pressing the evaporation of the flux _{Tl 2 Ba 2 Ca n-1} Cu n O 4 + 2n, the superconducting material It is extremely useful for industrial use.

Claims (1)

(57) [Claims] 1. A _{Tl 2 Ba 2 Ca n-1} Cu n O 4 + 2n (n =
An oxide superconductor single crystal represented by (1, 2, 3)
1 or a production method using KCl + NaCl or PbCl ₂ as a flux, characterized in that boron oxide (B ₂ O ₃ ) is added to a mixed powder forming an oxide superconductor material. Method for producing body single crystal.