JPH0360497A - Production of superconducting pseudo single crystal - Google Patents

Abstract

PURPOSE:To obtain the superconducting pseudo single crystal which can increase a current density by generating an eddy current in a polycrystalline superconductor to orient the C-axis of an orthorhombic crystal to a specified direction, then passing the current in the direction perpendicular to the C-axis. CONSTITUTION:The C-axis of the orthorhombic crystal is oriented in the specified direction by generating the eddy current in the polycrystalline superconductor. The current is then passed in this polycrystalline superconductor in the direction perpendicular to the C-axis thereof to orient the a-axis and b-axis to the specified direction by which the desired single crystal is obtd. The polycrystalline superconductor which is oriented in the a-axis, b-axis and c-axis to the specified direction by the above-mentioned production process is the pseudo single crystal conductor extremely approximate to the single crystal and, therefore, the critical current Jc is greatly improved. The superconducting sintered body having 3500/cm<2> critical current is produced by this method. Further, the additionally higher critical current is obtd. by making the careful operation.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application) The present invention relates to a method for producing superconducting pseudo-single crystals that can increase current density.

(Prior art) Conventionally, the method for manufacturing sintered superconducting composite oxides involves weighing a predetermined amount of powder of component element oxides or carbonates, mixing them thoroughly, shaping them, and pre-sintering them at several 100'C. It is manufactured by pulverizing it again, molding it, and firing it at about 900 to 1100°C.

The superconducting sintered body obtained in this way is polycrystalline,
When the crystal structure is orthorhombic, the lattice constants of the a, b, and c axes are (,4). Not yet.

In addition, the electric conductivity δ in these axial directions is the largest for a@, the b-axis is slightly smaller than the a-axis, and the C-axis is extremely small compared to the a-axis, about 1/1000, and is expressed by the following formula. be able to.

δa>δb>>δC Currently, the critical current Jc of the polycrystalline sintered body is 10+A/cm2
(77K), but in practical terms it is 10 A/cm2 without a magnetic field and 10 A/cm2 under an IOT magnetic field.
A/cm of 2nd place is requested.

The reason why the critical current JC of the polycrystalline sintered body is low is that the sintered density is not high enough, so there is insufficient contact between the polycrystalline grains, and the grain boundaries of the polycrystalline grains are not strong enough to withstand high current density. The problem is that the superconductivity of particles that are oriented unfavorably to the direction of the magnetic field or current due to the large anisotropy of the crystal breaks down quickly.

Regarding the critical current JC of polycrystalline sintered bodies, there is a concern that the critical current JC may reach a ceiling in some areas due to the low carrier density, short coherence length, etc.

However, on the other hand, the critical current Jc is 1 in an oriented polycrystalline thin film.
0 A/crn2, single crystal thin film r10', A, 70m
It is also true that 2 has been obtained.

(Problems to be Solved) The present invention seeks to provide a method for manufacturing a superconducting crystal which can increase the critical current JC of a polycrystalline superconductor and which can be put to practical use.

(Means for solving the problem) The present invention provides a polycrystalline superconductor in a state extremely close to that of a single crystal (
The aim is to improve the critical current JC by making it a superconducting pseudocrystal.

In the case of an orthorhombic polycrystalline superconductor, a@b@, C
The objective can be achieved by aligning and orienting the axes in a certain direction.

The first step is to align the C-axis.

The method will be explained in detail below.

A polycrystalline superconductor is placed inside a high-frequency coil, and a high-frequency current is passed through the coil at 450. ．． Temperatures below the phase transition point of 600°C (for example, the phase transition point of YBa-based superconductors is 570°C)
) to heat the polycrystalline superconductor.

In this case, an eddy current is induced in a crystal whose C-axis is parallel to the axial direction of the changing magnetic field, and the crystal's temperature increases and the crystal eventually disappears due to thermal motion.

On the other hand, in a crystal whose C-axis is perpendicular to the axial direction of the changing magnetic field, no eddy current is induced, the temperature of the crystal does not change, and the crystal grows using the crystal that has disappeared due to thermal motion as a raw material.

Furthermore, at least one of the polycrystalline superconductor or the coil is rotated about a direction perpendicular to the direction of the changing magnetic field.

This rotation does not have to be continuous. For example, when a polycrystalline superconductor is rotated in a fixed direction perpendicular to the coil axis, the rotation axis and the C axis coincide.

By the above method, the C-axes can be aligned and oriented in a certain direction.

Next, the second step is to align the a and b axes.

The method will be explained in detail below.

A current is passed in the direction perpendicular to the C-axis direction aligned in the first step, and 4
The polycrystalline superconductor is heated to a temperature below the phase transition point of 50-600'C.

The current may be direct current, alternating current or electrostatically induced.

In this case, more current flows through the crystal along the a-axis parallel to the current flow, and the temperature of the crystal increases and the crystal eventually disappears due to thermal motion.

On the other hand, since there is little current flow in the crystal along the a-axis perpendicular to the current flow, the temperature of the crystal does not rise that much, and the crystal grows using the crystal that has disappeared due to thermal motion as a raw material.

By the above method, the a-axis and the b-axis can be aligned and oriented in a certain direction.

The polycrystalline superconductor in which the a-axis, b-axis, and c-axis are oriented in a certain direction according to the present invention is a drum-wheel crystal superconductor that is extremely close to a single crystal, and therefore the critical current Jc can be significantly improved. .

The present inventors have achieved a critical current of 35000 A/c according to the present invention.
It was possible to produce a superconducting sintered body of m2. It is fully expected that even higher critical currents can be obtained by more careful operation.

(Effects of the Invention) According to the present invention, the polycrystalline superconductor can be made into a pseudocrystalline structure that is extremely close to a single crystal, so that the critical current can be significantly improved.

Claims (1)

[Claims] After aligning the C-axis of the orthorhombic crystal in a certain direction by generating an eddy current in the polycrystalline superconductor, a current is passed through the polycrystalline superconductor in a direction perpendicular to the C-axis to align the a- and b-axes. A method for producing a superconducting pseudo-single crystal characterized by orienting the crystals in a certain direction.