Microstructures of YBaCu superconductors with slight deviations from the 1-2-3 cation stoichiometry

The microstructures of YBa2Cu3O7-δ ceramics prepared from freeze-dried powders were studied by analytical electron microscopy. Nearly stoichiometric material and materials with compositions rich in Ba and Cu were sintered in air at 900C. Depending on the composition, both clean boundaries and boundaries containing a secondary phase were found in the materials. Fine scale analyses of compositional variations near the interfaces are presented. With increasing deviation from the 1-2-3 stoichiometry, the secondary phases were observed to display a morphology and distribution that is related to the liquid present at the sintering temperature. The grain growth of the 1-2-3 phase was also strongly influenced. The microstructures are related to the superconducting properties