Role of PtO2 on the refinement of Y2BaCuO5 second phase particles in melt-textured Y-Ba-Cu-O oxides

In order to understand the mechanism of the Y2BaCuO5 (Y211) refinement, the effect of PtO2 addition on the microstructure of each reaction state, i.e., the solid state, the Y211 plus liquid state and the peritectic growth state of the melt-texture YBa2Cu3O7-y (Y123), was investigated. When heating a mixture of a Y123 powder and PtO2 powder below the peritectic temperature of Y-Ba-Cu-O, the PtO2 reacts with a Y123 phase and then forms a Pt-bearing compound via the solid state reaction. As a result of this reaction, free CuO is produced and it leads to the p1 pseudo-peritectic reaction of Y123 + CuO --> Y211 + liquid. The produced Y211 particles by the p1 pseudo-peritectic reaction were acicular in shape. They serve as a seed for the growth of the Y211 formed by m1 peritectic melting of Y123 --> Y211 + liquid, resulting in the formation of acicular Y211 particles at the Y211 plus liquid state. A liquid infiltration experiment with/without PtO2 addition into a Y211 compact at 1100 degrees C showed that Y211 coarsening in the liquid phase containing PtO2 was less significant than that in the liquid containing no PtO2. It is concluded that PtO2 addition suppresses the Y211 growth in the liquid phase as well as changes its morphology. (C) 1997 Elsevier Science B.V.