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 behavi or of high-purity stoichiometric BaTiO3 have been intensively investig ated. It was found that the dielectric constant was influenced not onl y by grain size but also by pore morphology. Dielectric constants belo w 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 c onstants could be separated into two regions depending on the pore mor phology, decreasing linearly with increasing porosity at different rat es. The results suggest that the tetragonal-cubic phase transition tem perature 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) microstruc ture of high-purity stoichiometric barium titanate has been produced b y using wet processing and pressureless sintering, in which a high die lectric constant (>6100 at 25-degrees-C and 1 kHz) and a low dissipati on factor (<0.025) could be achieved.