JPH05105573A - Production of oxide superconductor single crystal - Google Patents

Abstract

PURPOSE:To synthesize a high-quality large-sized single crystal of an oxide superconductor by a standing slow-cooling method. CONSTITUTION:A single crystal is produced by carrying out the standing slow- cooling of synthesized raw material powder while blasting a gas to a crucible 4, thereby applying effective temperature gradient. For example, a powdery mixture having the composition of Tl2Ba2CuO6+KCl is sealed in a gold crucible 4 and slowly cooled from 920 deg.C at a cooling rate of 5 deg.C/hr while blasting oxygen gas to a point on the upper part of the crucible. The growth of ten odd number of single crystals of several mm square and about 0.01 mm thick is observed around the part blasted with the gas and the crystal exhibits sharp transition to superconductivity at 85K. (When the above process is carried out under the same condition except for the blast of gas, there is no growth of single crystal and only powder is deposited on the bottom of the crucible.)

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 has also been applied to medical equipment such as NMR-CT and floating linear motors. Considering the application of superconductors, the superconducting transition temperature Tc is desired to be as high as possible. Metal-alloy superconductors and compound superconductors must use expensive and rare liquid helium as a refrigerant, which is one of the factors that hinder the application of these superconductors to a wide range of fields. ing. In this respect, the copper oxide-based superconductor is far superior to the conventional superconductor.
Since the Ba-Y-Cu-O-based superconductor was discovered in 1987, Bi-Sr-Ca-Cu-O-based and Tl-Ba-Ca
Superconductors having a Tc above the liquid nitrogen temperature, such as the —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 a polycrystalline superconductor sample, it is difficult to make a Josephson junction with desired properties with good controllability because there are numerous 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. Among the methods for synthesizing a single crystal, a static annealing method is a relatively simple method. This method has the advantage that crystals can be synthesized without using a special electric furnace that has a moving mechanism for the crystal and the crucible, but the temperature gradient in the crucible is determined by the natural temperature gradient of the electric furnace, so When using a horizontal furnace such as a good diffusion furnace, it becomes difficult to synthesize a single crystal. The object of the present invention is to synthesize an oxide superconductor by a stationary annealing method,
It is an object of the present invention to provide a method for producing a good-quality oxide superconductor single crystal having a sufficient size by introducing an appropriate temperature gradient into the crucible.

[0004]

The present invention is a method for producing an oxide superconductor single crystal, characterized in that when a crucible containing a raw material for crystal synthesis is gradually cooled, it is carried out while blowing a gas. It is a method for producing a superconductor single crystal.

[0005]

After the mixed powder having the composition of Tl ₂ Ba ₂ CuO ₆ + KCl is sealed in the metal crucible, oxygen gas is blown to one point on the upper part of the crucible from 920 ° C to the slow cooling rate of 5 ° C / hou.
When gradually cooled with r, a single crystal having a size of several mm square and a thickness of about 0.01 mm centering on the position where the gas was blown was 10
It was confirmed that some of them were growing. These crystals showed a sharp superconducting transition at 85K. When the gas was not blown under the same conditions, a single crystal was not obtained and only powder was formed on the bottom of the crucible.

[0006]

EXAMPLES The present invention will be specifically described below with reference to examples. Example 1 As a starting material, thallium oxide (T
l ₂ O ₃ ), barium oxide (BaO), cupric oxide (Cu
O) and potassium chloride (KCl) were used. First, Tl
_The powder mixed with ₂ O ₃ + 2BaO + CuO was pressed and then fired at 860 to 870 ° C. to give Tl ₂ Ba ₂ CuO ₆
A sintered body was synthesized. The powder of the obtained sintered body and KCl were mixed and sealed in a 20 mmφ × 25 mm metal crucible, and then placed on a quartz boat 2 of 50 mm wide × 20 mm high with a 10 mmφ quartz tube 1 shown in FIG. It was inserted into the diffusion furnace. The diameter of the nozzle 5 is selected according to the size of the crucible 4 and the amount of blowing gas required. The maximum temperature during crystal synthesis is 920
℃, the slow cooling rate was 5 ℃ / hour. The crystals were taken out by flushing KCl with water. FIG. 1 shows the configuration of an electric furnace which is a synthesizer. In this device, the amount of gas flowing through the entire furnace core tube 3 and the amount of gas blown onto the crucible 4 can be controlled independently. Table 1 shows the total amount of gas L1 (l / min) and the amount of gas L2 sprayed on the crucible.
(L / min) and the size of the obtained crystal are shown. In the case where the gas was not blown (L2 = O), the temperature in the crucible was extremely uniform under this cooling condition, and no visible size crystal was formed. When the gas was blown, ten or more single crystals were grown around the place where the gas was blown, and the average size was several mm square × 0.0.
It was about 1 mm.

[0007]

[Table 1] Size of Tl ₂ Ba ₂ CuO ₆ single crystal obtained from Tl ₂ BaCuO ₆ + KCl ───────────────────────────── ────── Sample L1 L2 Size number (l / min) (l / min) (mm) ─────────────────────────── ──────── 1 5 0 Powder accumulated on the bottom of the crucible 2 4 1 2 * 2 * 0.01 3 4 2 3 * 3 * 0.04 4 3 2 5 * 5 * 0.05 5 2 3 5 * 5 * 0.04 6 1 4 4 * 4 * 0.03 7 0 5 4 * 4 * 0.02 ──────────────────────────────────

Example 2 Bismuth oxide (Bi ₂ O ₃ ), strontium oxide (SrO), calcium oxide (CaO), and copper oxide (CuO) were used as starting materials. These raw materials are Bi: Sr: C.
a: Cu = 2: 2: 2: 5 and mixed in a platinum crucible, set in the quartz tube with a glass tube described in Example 1, and set in a diffusion furnace at 950 ° C. to 10 ° C./hour. Cooled in. Flux CuO and Bi ₂ Sr ₂ CaCu ₂
The mixed lump of O ₈ single crystal was broken with a chisel to take out the crystal. Table 2 shows the gas amount and crystal size. In this case as well, the crystals obtained are small when gas is not blown.
The size of the crystals obtained by gas blowing is improved.

[0009]

[Table 2]Bi ₂ O ₃ + SrO + CaO obtained from + 2.5CuO Bi ₂ Sr ₂ CaCu ₂ Size of O ₈ single crystal ───────────────────────────────── Sample L1 L2 Size number (l / min) (l / min) (mm ) ───────────────────────────────── 8 10 0 0.2 * 0.2 * 0.01 9 8 2 1 * 1 * 0.03 10 6 4 5 * 5 * 0.08 11 4 6 8 * 8 * 0.1 12 2 8 8 * 8 * 0.1 13 0 10 7 * 7 * 0.09 ─────────────────── ───────────────

[0010]

According to the manufacturing method of the present invention, a large-sized oxide superconductor single crystal of good quality can be obtained, which is extremely useful for industrial use of superconducting materials.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an example of a single crystal synthesizing apparatus used in a method of the present invention.

FIG. 2 is a quartz tube with a quartz tube used in the method of the present invention.
FIG.

[Explanation of symbols]

 1 Quartz tube 2 Quartz boat 3 Furnace core tube 4 Crucible 5 Nozzle

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Taku Kondo 5-7-1 Shiba, Minato-ku, Tokyo NEC Corporation

Claims (1)

[Claims] 1. A method for producing an oxide superconductor single crystal, which is characterized in that a gas is blown when gradually cooling a crucible containing a raw material for crystal synthesis. Method.