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-xCa xCO3 precursors used in this method were prepared by a chemical coprec ipitation route to ensure a uniform supply of Ba and Ca ions during th ermochemical reaction with TiO2. The compositional homogeneity of Ba1- xCaxTiO3 powder prepared by such a semiwet route is compared with thos e prepared by the conventional dry route, involving thermochemical rea ction in a mixture of BaCO3, CaCO3, and TiO2, using principles of X-ra y line broadening. It is shown that the powders obtained by the semiwe t route possess better compositional homogeneity, over a length scale of 1800 angstrom corresponding to the coherently scattering domain siz e, than those prepared by the conventional dry route. Microstructural studies have revealed grain sizes of the order of 1 mum and several mi crometers, respectively, for ceramics prepared by the semiwet and conv entional dry routes. The solid solubility limit of Ca in Ba1-xCaxTiO3 ceramics fired at 1300-degrees-C is 16 mol % for samples prepared by t he semiwet route while conventionally processed ceramics had a Ca soli d solubility limit of 12 mol % at the same temperature.