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 region, microstructures concerning incongruent melting and peritectic reaction were studied in melt-textured Y-Ba-Cu-O oxides. It is found that spherical pores form during incongruent melting of the YBa2Cu3O7-y phase 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 the sample from the peritectic temperature to the temperature where YBa2Cu3O7-y phase is formed, the liquid pockets are converted into YBa2Cu3O7-y phase containing a few Y2BaCuO5 particles. Sometimes, remnant Ba-Cu-O liquid phase is present at the center part of the Y2BaCuO5 free regions 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.