Effect of silver addition on the microstructure of YBa2Cu3O7-x

The variation of grain morphology in silver-doped YBa2Cu3O7-x was investigated as a function of sintering temperature, atmosphere, and amount of Ag addition. In the presence of the liquid phase formed at 925 degree C for undoped samples, and at 910 degree C for silver-doped samples, the grain shape and size changed drastically from small and nearly equiaxed to large and elongated. The anisotropy in the grain shape was sensitive to both the silver content and the atmosphere. On the other hand, while the grain size was generally insensitive to the atmosphere, it decreased as the silver content increased. The silver phase, if sufficiently large, would block the grain growth in the matrix. The amount of silver for effective blocking was predicted from a microstructural model, and the prediction was in agreement with experimental results