MODIFIED MELT TECHNIQUES FOR HIGH JC YBCO PREPARATION

Critical current density of YBCO ceramics proved to be very sensitive to microstructure peculiarities. Variation of thermal regimes, tempera ture gradient and gas atmosphere is commonly used for the microstructu re control. Specific crystalline structure of 123 phase provides anoth er unique possibility connected with substitution of Y by similar rare earth elements. It does not destroy superconducting structure but may change thermal stability of (REE, Y)Ba(2)Cu(3)Ox phases. A method bas ed on ''chemical supercooling'' control under melt crystallization con ditions followed by selective crystallization of R,Y-123 HTSCs from mu lticomponent melts was successfully applied to high J(c) HTSCs formati on with desirable final microstructure and HTSC properties.