Unidirectional Partial Melting and Solidification of SmBCO Superconductor

Abstract

Microstructure control of the SmBCO superconductor was carried out using the floating zone partial melting and solidification method. It is generally recognized that finely and uniformly dispersed nonsuperconductive high temperature stable phase (Sm211) particles included in the superconductive Sm123 matrix act as effective pinning centers. Microstructure formation of the partial molten mixture (Sm211 particles and BaO–CuO liquid) by decomposition of the precursor Sm123 on melting and solidification of Sm123 from the mixture have to be controlled concurrently to fabricate the 123/211 composite fiber with the optimum microstructure. During unidirectional solidification, planar crystal growth which provides the single crystal growth of Sm123 becomes unstable with increased growth rate. During unidirectional melting, the mean diameter of aligned Sm211 particles behind the melting interface decreases with increased growth rate and with decreased temperature gradient at the melting interface. Initial composition of the precursor significantly affects the formation behavior of Sm211 particles. The contribution of process parameters to the microstructure formation is also briefly discussed.