JPH01264957A - Superconducting material - Google Patents

Abstract

PURPOSE:To form a pin stopping center within the grain boundary of a superconductor in which the grain boundary exists in the form of bulk or thin film and to improve the critical current density thereof by adding a compd. contg. magnetic ions to said superconductor. CONSTITUTION:A small amt. of the compd. (e.g.: the oxide of Nd and Eu having the larger ion radius than Y among lanthanoid groups in case of the system of the base material in the undermentioned example) contg. the magnetic ions which have sufficiently low reactivity with the superconductor, i.e., the base material and do not extremely deteriorate the superconducting characteristic of the base material is added to the raw materials (e.g.: Y2O3, BaCO3, CuO) at the time of producing the base material of the oxide superconductor (e.g.: Y, Ba, Cu, O system) in which the grain boundary exists in the form of bulk or thin film. The raw materials are calcined, ground and molded and the molding is calcined again and is slowly cooled, by which the superconducting material intentionally added with the compd. contg. the magnetic ions is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to superconducting materials. In the present invention, in a superconductor where grain boundaries exist, by adding a compound containing a small amount of magnetic ions, these magnetic ions are precipitated at the grain boundaries, and by controlling the grain boundaries, the superconducting critical current value (hereinafter referred to as The objective is to improve the

“Future technology” In recent years, oxide superconductors with high critical temperatures (such as YB
(CO, etc.) was discovered, and research is being conducted into making wire rods as one of its practical applications. However, Jc calculated from measurements of magnetic susceptibility is as large as 77 to 10'A/cm, whereas in actual samples it is currently not possible to obtain a Jc high enough to be of practical use. The main reason for this has been said to be that grain boundaries in superconductors act as Josephson weak bonds.

However, as a result of a more detailed study, the inventors found another cause for the low Jc. In this grain boundary region, impurities precipitate as a superconducting phase forms, forming a kind of layer. This state is more like a tunnel junction than a weak coupling. Therefore, it is thought that superconductors have many long tunnel junctions. Such tunnel junctions are commonly called Josephson lines. When a magnetic field is applied, magnetic flux enters this junction,
When a current flows, the magnetic flux begins to move due to the Lorentz force,
This creates a voltage, or resistance, across the junction. It is thought that Jc is low because the binding force is weak at the grain boundaries of the oxide superconductor. One of the reasons for this is the fact that Jc is extremely depressed by the magnetic field.

``Structure of the invention'' These problems G can be solved if the binding force of grain boundaries can be strengthened. In alloy superconductors, grain boundaries, dislocations, etc. were used as places to bind the magnetic flux, that is, as centers of the bind, but in this oxide superconductor, the places where the magnetic flux is bound are confined within the grain boundaries. Therefore, it is difficult to create a center. By the way, there is an idea that superconductors containing magnetic ions (JC) can be made larger.The basis for this is that the magnetic ions are thought to act as the center of the bottle. We thought that if magnetic ions were precipitated at the grain boundaries, they would act as binding centers and improve Jc. However, the magnetic ions scattered at the grain boundaries either did not react with the base material or did not react with the base material. However, if YBCO is to be used as the base material, the inventors of the present invention have determined that if YBCO is to be used as the base material, the lanthanide group should be used. Among these, it has been found that oxides of neodymium (Nd) and europium (Eu), which have larger ionic radii than yttrium (Y), are suitable.The present invention will be explained in more detail by showing examples below.

"Example" YBCO was used as the base material. For comparison, we created samples with and without magnetic ions added. Sample 1~
The composition ratio (molar ratio) of No. 4 is as follows.

The sample was prepared by solid phase reaction method. That is, after thoroughly mixing the raw material powders, they were calcined in the air at 900 degrees for 12 hours, and the calcined product was pulverized to produce a powder of 1000 kg/cm.
Formed into pellets at a pressure of
After sintering for an hour, it was slowly cooled at a cooling rate of 100 degrees/hour.

Each pellet was formed into a rectangular parallelepiped of approximately 10 mm x 1 mm x 1 mm, and electrical bridges were attached with silver paste. Sample 1~
The superconducting properties of No. 4 were as shown in Table 1. As can be seen from comparing Sample 1 with other Samples 2 and 3, an improvement in Jc (particularly during application of a magnetic field) is clearly seen. The poor characteristics of sample 4 were due to the addition amount being too large, and X-ray diffraction revealed that
A so-called green phase Y28aCuO3 is observed.

However, Jc was defined as 1 μV/mm.

Although this example describes a YBCO-based superconductor, the same effect can be expected for a BaLACuO-based Bi-based superconductor. Compounds to be added include Ce, Pr, Nd, Pm, Sm, and Eu.

It is possible to use oxides such as

[Effect] By adopting the configuration of the present invention, a binding center is formed within the grain boundaries of an oxide superconductor, and a superconductor with a large JC (1) W field current density) can be easily realized. was completed.

Claims (1)

[Scope of Claims] 1. A superconducting material in which a compound containing magnetic ions is intentionally added to a superconductor in the form of a bulk or thin film in which grain boundaries exist. 2. In claim 1, the compound containing magnetic ions has sufficiently low reactivity with the superconductor that is the base material,
A superconducting material characterized by not significantly deteriorating the superconducting properties of a base material.