EFFECTS OF PORE MORPHOLOGY AND GRAIN-SIZE ON THE DIELECTRIC-PROPERTIES AND TETRAGONAL CUBIC PHASE-TRANSITION OF HIGH-PURITY BARIUM-TITANATE

The effects of pore morphology and grain size on the dielectric behavior of high-purity stoichiometric BaTiO3 have been intensively investigated. It was found that the dielectric constant was influenced not only by grain size but also by pore morphology. Dielectric constants below the Curie temperature could be evaluated by the Maxwell relationship for specimens with fractional density >90% rho(t) and be estimated by the modified Niesel's equation, but depolarization might be involved for specimens with fractional density <90% rho(t). Dielectric behavior above the Curie temperature followed the Curie-Weiss law. The Curie constants could be separated into two regions depending on the pore morphology, decreasing linearly with increasing porosity at different rates. The results suggest that the tetragonal-cubic phase transition temperature of specimens with fractional density <90% rho(t) is affected by depolarization due to the presence of continuous channel pores. The dissipation factor was increased with increasing porosity due to the adsorption of water. In this study, a high-density (approximately 99 % rho(t)), uniform, and fine-grained (approximately 1.2 mum) microstructure of high-purity stoichiometric barium titanate has been produced by using wet processing and pressureless sintering, in which a high dielectric constant (>6100 at 25-degrees-C and 1 kHz) and a low dissipation factor (<0.025) could be achieved.