Unidirectional microstructure formation of Sm-Ba-Cu-O superconductor on melting via peritectic reaction

In this paper, solidification microstructure control of a partial molten mixture is discussed. Since finely dispersed non-superconductive high temperature stable phase (Sm2Ba1Cu1O5, Sm211) particles in the superconductive Sm1Ba2Cu3O7-d (Sm123) can act as effective pinning centers and grain boundaries play as weak-links of electric transport, single crystalline Sm123 with finely dispersed Sm211 particles is required to improve the critical current density (J(c)). To obtain the bulk single crystalline Sm123 with fine Sm211 particles by floating-zone partial melting and the solidification method, the microstructure of the partial molten mixture (Sm211 particles and liquid) is to be controlled, because the solidification microstructure of Sm123/211 is mainly determined by that of the mixture. During unidirectional melting, the mean diameter, d(211), (or spacing, lambda) of rod-likely aligned Sm211 particles after decomposition of the precursor Sm123 decreased with increasing growth rate, R. The mean diameter d(211) became larger under P-O2=1 kPa atomsphere than that at atomspheric pressure. Based upon the experimental results, a simple model for the formation of aligned Sm211 particles via peritectic decomposition was proposed, and prediction from the model was compared with the experimental results. Effects of melting conditions on the microstructure formation of the partial molten mixture were discussed.