Ferroelectrics of Ultrafine Particle Size: II, Grain Growth Inhibition Studies

Inhibition of grain growth in pure, fine-particle-size barium titanate bodies by coating the surfaces of the barium titanate particles with tantalum oxide was so effective that doping with a sintering aid was necessary for densification of the bulk material at temperatures below the melting point. A correlation, which was independent of starting particle size, was established between inhibitor concentration and final grain size of the fired bodies. Barium titanate bodies of predetermined grain size not larger than 2000 A were obtained even with extended firing schedules. In the smallest grain sizes, the Curie point was shifted below the measured temperature range, and hysteresis losses were reduced markedly. The dielectric constant had a smooth variation from approximately 3000 at room temperature to 800 at 180°C.