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 incongraent mehing 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 YBa₂Cu₃O_7−y phase into Y₂BaCuO₃ and a Ba–Cu–O liquid phase. As the melting goes on, 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 YBa₂Cu₃O_7−y phase is formed, the liquid pockets are converted into YBa₂Cu₃O_7−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 YBa₂Cu₃O_7−y is responsible for the formation of the Y₂BaCuO₅ free regions.