Processing and properties of QMG materials

Abstract

Recent progress of Quench and Melt Growth (QMG) process is reviewed. QMG process is one of the melt processes for Y based superconductor. A pseudo single crystal (QMG crystal) which includes finely dispersed 211 phase in the matrix of 123 phase was produced by the original QMG process. The critical current density of the QMG crystal that has no high angle grain boundaries has been exceeding 10 4A/cm 2 at 77K and 1T. The original QMG process was improved to make larger QMG crystals of which crystallographic orientation was controlled. Modified QMG process can be characterized by Pt addition in precursor preparation and seeding technique in growth process. Crystallinity of the QMG crystal made by this modified process was investigated. It appeared that there were two kinds of domain structures that depend on the growth direction. QMG crystals enlarged by this modified process are applicable to various fields. For instance, QMG crystal can operate as a bulk magnet. The maximum value of flux density was 4.5T at 40K on the surface. It was found that QMG crystal is thermally stable above 40K at least.