STRUCTURE AND PROPERTIES OF (BA,CA)TIO3 CERAMICS PREPARED USING (BA,CA)CO3 PRECURSORS .1. CRYSTALLOGRAPHIC AND MICROSTRUCTURAL STUDIES

Ba1-xCaxTiO3 powders have been prepared using a novel route involving solid-state reaction in a mixture of Ba1-xCaxCO3 and TiO2. The Ba1-xCaxCO3 precursors used in this method were prepared by a chemical coprecipitation route to ensure a uniform supply of Ba and Ca ions during thermochemical reaction with TiO2. The compositional homogeneity of Ba1-xCaxTiO3 powder prepared by such a semiwet route is compared with those prepared by the conventional dry route, involving thermochemical reaction in a mixture of BaCO3, CaCO3, and TiO2, using principles of X-ray line broadening. It is shown that the powders obtained by the semiwet route possess better compositional homogeneity, over a length scale of 1800 angstrom corresponding to the coherently scattering domain size, than those prepared by the conventional dry route. Microstructural studies have revealed grain sizes of the order of 1 mum and several micrometers, respectively, for ceramics prepared by the semiwet and conventional dry routes. The solid solubility limit of Ca in Ba1-xCaxTiO3 ceramics fired at 1300-degrees-C is 16 mol % for samples prepared by the semiwet route while conventionally processed ceramics had a Ca solid solubility limit of 12 mol % at the same temperature.