CRYSTAL-CHEMISTRY OF THE TEXTURE FORMATION IN SUPERCONDUCTIVE YBA2CU3O7-DELTA CERAMICS

Classical sintering of YBa2Cu3O7-delta always leads to poor critical transport currents whatever the powder process and the thermal cycle are. Best results are obtained by synthesis of textured ceramics. Fabrication of YBa2Cu3O7-delta with well-oriented grain structure by the melt textured growth process was performed in order to understand the mechanism that controls the texture formation. The evolution of the microstructure was studied by quenching samples at different stages of the MTG cycle. The importance in the texture formation process of the presintering temperature, of the high temperature plateau, of the thermal gradient and its fluctuations, of the presence of second phase inclusions (essentially 211 phase), and of the substrate and its reactivity with Y-Ba-Cu-O is shown.