ORIGIN OF THE Y2BA1CU1O5 FREE REGION IN MELT-TEXTURED Y-BA-CU-O OXIDES

In order to understand the formation mechanism of the Y2BaCuO5 free re gion, microstructures concerning incongruent melting and peritectic re action were studied in melt-textured Y-Ba-Cu-O oxides. It is found tha t spherical pores form during incongruent melting of the YBa2Cu3O7-y p hase into Y2BaCuO5 and a Ba-Cu-O liquid phase. As the melting goes an, liquid phase flows into the pores and then produces spherical liquid pockets containing a few Y2BaCuO5 particles. During slow cooling of th e sample from the peritectic temperature to the temperature where YBa2 Cu3O7-y phase is formed, the liquid pockets are converted into YBa2Cu3 O7-y phase containing a few Y2BaCuO5 particles. Sometimes, remnant Ba- Cu-O liquid phase is present at the center part of the Y2BaCuO5 free r egions due to the incomplete peritectic reaction. It is concluded that formation of spherical pores during incongruent melting of YBa2Cu3O7- y is responsible for the formation of the Y2BaCuO5 free regions.