Y2BACUO5 MORPHOLOGY IN MELT-TEXTURED Y-BA-CU-O OXIDES WITH PTO2H2O/CEO2 ADDITIONS

Microstructures related to the 2-1-1 morphology, and the effect of PtO2.H2O and CeO2 additions on 2-1-1 refinement were examined in melt-textures Y1Ba2Cu3O7-y and Y1.6Ba2.3Cu3.3O7-y systems. It is found that the characteristics of 2-1-1 nucleation and growth is considerably affected by the additives and the microstructure prior to peritectic decomposition. In the Y1Ba2Cu3O7-y system, without an additive, block-like 2-1-1 particles are produced when the 1-2-3 phase was decomposed into 2-1-1 and a Ba-Cu-O liquid phase. PtO2.H2O addition changes the 2-1-1 shape to be highly anisotropic while CeO2 addition reduces the 2-1-1 size as well as making it anisotropic. In the Y1.6Ba2.3Cu3.3O7-y system where excess 2-1-1 particles are present prior to melting, the excess 2-1-1 acts as a grain-growth inhibitor for the 1-2-3 phase at the sintered state and thus results in a fine-sized 1-2-3 grain structure which provides nucleation sites for formation of the 2-1-1 phase. Also, the excess 2-1-1 particles appear to act as heterogeneous nucleation sites for the decomposed 2-1-1. Without the additives, equiaxed 2-1-1 particles are produced while with additives, fine granular or plate-like 2-1-1 particles are produced. The resulting 2-1-1 shape is fairly dependent on the shape of the 2-1-1 particles formed at the sintered state, indicating the heterogeneous nucleation of the 2-1-1 on the prior 2-1-1.