JPH05279191A - Production of oxide superconductor single crystal - Google Patents

Abstract

PURPOSE:To enable the growth of a large-sized single crystal of a Tl-based oxide superconductor by using a KCl/LiCl eutectic flux having low melting point and growing a single crystal by stationary slow-cooling process. CONSTITUTION:A KCl/LiCl eutectic flux having low melting point is used as a flux. A powdery mixture having a composition falling within the range expressed by formula I (2<=x<=500; 0.05<=y<=1; (n) is 1-3) or formula II is prepared by using high-purity thallium oxide, barium oxide, calcium oxide, cupric oxide, potassium chloride and lithium chloride as starting raw materials. The powdery mixture is melted at 500-950 deg.C and slowly cooled by stationary slow- cooling process at a cooling rate of <=10 deg.C/hr to obtain the objective oxide superconductor single crystal expressed by the formula Tl2Ba2Can-1CunO6 ((n) is 1-3).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxide superconducting material used in various superconducting devices and superconducting devices.

[0002]

2. Description of the Related Art Metal / alloy type superconducting materials and compound superconducting materials have already been widely used as wire rods for Josephson devices and superconducting magnets. The Josephson junction has been applied to precision measurement including SQUID because of its high sensitivity to a magnetic field, and is expected to be applied to an electronic computer because of its high speed. In addition, a superconducting magnet that can generate a high magnetic field that cannot be obtained with a normal conductor is
It is also applied to medical equipment such as NMR-CT and floating linear motor cars. Considering the application of superconductors, the superconducting transition temperature (Tc) is desired to be as high as possible. Metal / alloy superconductors and compound superconductors
Liquid helium, which is expensive and rare, must be used as a refrigerant, which is one of the factors that hinder the application of these superconductors to a wide range of fields. In this respect, copper oxide-based superconductors are far superior to conventional superconductors.
Since the Ba-Y-Cu-O system superconductor was discovered in 987, Bi-Sr-Ca-Cu-O system, Tl-Ba-C system
Superconductors having a Tc above the liquid nitrogen temperature such as a-Cu-O system have been discovered one after another. If these oxide superconductors are put into practical use, the possibility of their application will be expanded to fields that were previously unthinkable, and research and development are still being actively conducted.

[0003]

Most of the oxide superconductor samples currently studied are polycrystalline. In the polycrystalline sample of superconductor, it is difficult to make Josephson junctions with desired characteristics with good controllability because there are innumerable weak superconducting bonds at the grain boundaries. Further, various defects and inhomogeneities contained in the polycrystal may adversely affect the stability of the superconducting property, so that it is desirable to use the monocrystal for application to devices and the like. There is an example of using KCl as a flux in the method of synthesizing a superconductor single crystal by the stationary gradual cooling method, but since the melting point of KCl alone is as high as 770 ° C. Can't be trained. This is a major obstacle when trying to produce only the desired crystal in a system containing several phases having the same composition but different formation temperatures. In view of such conventional circumstances, it is an object of the present invention to provide a method for growing a Tl-based superconductor single crystal sample having a good quality and a sufficient size in a wide temperature range.

[0004]

SUMMARY OF THE INVENTION The present invention is directed to Tl ₂ Ba ₂ C
a _n-1 Cu _n O ₆ (where n is 1, 2 or 3)
In the method for producing an oxide superconductor single crystal represented by,
Using a mixture of KCl and LiCl as a flux, Tl ₂ O ₃ + 2BaO + (n-1) CaO + nCuO + x
{(1-y) KCl + yLiCl} (2 ≦ x ≦ 500, 0.05 ≦ y ≦ 1, n = 1, 2 or 3) mixed powder having a composition range, or Tl ₂ Ba ₂ Can _n-1 Cu _n O _{4 + 2n} + x {(1-y) KCl
+ YLiCl} (2 ≦ x ≦ 500, 0.05 ≦ y ≦ 1, n = 1, 2 or 3) is mixed powder at 500 ° C. to 950 ° C.
And a slow cooling at a rate of 10 ° C./hour or less, which is a method for producing an oxide superconductor single crystal. That is, according to the present invention, KCl / Li having a low melting point is used in place of the KCl flux used so far.
It has been found that the use of the Cl eutectic flux makes it possible to grow a Tl-based single crystal at a low temperature of 500 ° C., which could not be conventionally grown.

[0005]

[Function] From the mixed powder of composition Tl ₂ O ₃ + 2BaO + CuO + 20KCl, the maximum temperature is 900 ° C, and the slow cooling rate is 10 ° C.
The single crystal made with / hour is 2mm square and thickness is 0.0
The size was about 1 mm. However, Tl ₂ O ₃ +2
The size of the crystal grown from the mixed powder of the composition BaO + CuO + 10KCl + 10LiCl under the same conditions was 5 mm square or more, and sharply transitioned to superconductivity at 85K.

[0006]

EXAMPLES Examples of the present invention will be specifically described below. Example 1 As a starting material, thallium oxide (T
l ₂ O ₃ ), barium oxide (BaO), calcium oxide (CaO), cupric oxide (CuO), potassium chloride (K
Cl), lithium chloride (LiCl), and Tl ₂ O ₃
+ 2BaO + (n-1) CaO + nCuO + x {(1-
y) KCl + yLiCl}, where n, x and y are weighed and mixed so that the compounding ratios shown in Table 1 are obtained.
Enclosed in a gold crucible with a diameter of 20 mm and a depth of 25 mm, 500
After melting at 1C to 950C for 1 to 10 hours, it was gradually cooled to 400C at a rate of 10C or less per hour. From 400 ° C. to room temperature, it was cooled at a rate of 100 ° C. for 1 hour. Single crystal samples were removed by flushing KCl and LiCl with water.

Example 2 The same reagent as in Example 1 was used as a starting material. First Tl ₂
O ₃ , BaO, CaO, CuO is replaced with Tl ₂ Ba ₂ Can _n-1 Cu
_The mixture was mixed so as to have a ratio of _n O _{4 + 2n} , pressed, and then wrapped with gold foil and sintered at 860 ° C. to 900 ° C. for 3 to 5 hours. The obtained sintered body was crushed to obtain KCl, LiCl, and Tl ₂ B.
_{a 2 Ca n-1 Cu n} O 4 + 2n + x {(1-y) KCl + yL
iCl}, and n, x, and y were mixed at the compounding ratio shown in Table 2. Melting, solidification, and taking out of the single crystal were performed under the same conditions as in Example 1.

In each case, the resistivity and diamagnetic susceptibility of the obtained single crystal were measured and the composition was analyzed. The resistivity was measured by a 4-terminal method using a gold wire as a lead, and the diamagnetic susceptibility was measured by an SQUID magnetometer. The composition analysis was performed using EPMA.

Tables 1 and 2 show typical sizes and Tc of the single crystals obtained. At a temperature of 950 ° C. or higher, Tl and flux vaporize excessively, which is unsuitable for single crystal growth. The closer the y is to 0.4, the lower the melting point of the flux, so the growth temperature can be lowered. If the amount of the raw material is too large compared to the amount of flux, large single crystals cannot be obtained because nucleation occurs at many places at the same time. Even if the amount of the raw material is too small, the single crystal does not grow sufficiently. Becomes smaller.

[0010]

[Table 1]

[0011]

[Table 2]

[0012]

As described above, according to the present invention, a high quality and large Tl-based superconductor single crystal sample can be manufactured in a wide temperature range.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H01L 39/12 ZAA 8728-4M

Claims (1)

[Claims] 1. Tl ₂ Ba ₂ Ca _n-1 Cu _n O ₆ (wherein n
Is 1, 2 or 3. ) In the method for producing an oxide superconductor single crystal represented by the formula: Tl ₂ O ₃ + 2BaO + (n-1) CaO + nCuO + x, using a mixture of KCl and LiCl as a flux.
{(1-y) KCl + yLiCl} (2 ≦ x ≦ 500, 0.05 ≦ y ≦ 1, n = 1, 2 or 3) mixed powder having a composition range, or Tl ₂ Ba ₂ Can _n-1 Cu _n O _{4 + 2n} + x {(1-y) KCl
+ YLiCl} (2 ≦ x ≦ 500, 0.05 ≦ y ≦ 1, n = 1, 2 or 3) is mixed powder at 500 ° C. to 950 ° C.
And a slow cooling at a rate of 10 ° C./hour or less, a method for producing an oxide superconductor single crystal.