Ultrafine barium titanate powders via microemulsion processing routes

Three processing routes have been used to prepare barium titanate powders, namely conventional coprecipitation, single-microemulsion coprecipitation using diether oxalate as the precipitant, and double-microemulsion coprecipitation using oxalic acid as the precipitant. A single-phase perovskite barium titanate was obtained when the double-microemulsion-derived oxalate precursor was calcined for 2 h at a temperature of as low as 550 °C, compared to 600 °C required by the single-microemulsion-derived precursor. A calcination for 2 h at >700 °C was required for the conventionally coprecipitated precursor in order to develop a predominant barium titanate phase. It was, however, impossible to eliminate the residual TiO₂ impurity phase by raising the calcination temperature, up to 1000 °C. The microemulsion-derived barium titanate powders also demonstrated much better powder characteristics, such as more refined crystallite and particle sizes and a much lower degree of particle agglomeration, than those of the conventionally coprecipitated powder, although they contained approximately 0.2 wt% BaCO₃ as the impurity phase.