Densification behaviour, microstructure development and dielectric properties of pure BaTiO 3 prepared by thermal decomposition of (Ba,Ti)-citrate polyester resins

Abstract

The thermal decomposition of (Ba,Ti)-citrate polyester resin method was used to prepare high purity BaTiO 3 powders. After milling, the green compacts’ uniformity was studied using both the SEM observations on surfaces of the fractured green compacts, and the pore size distribution results obtained by using Hg-porosimmetry. The densification behaviour was found to be closely related to the pore distribution in the powder compacts and, thus, the different maxima in the pore size distribution were assumed to be connected to the maxima in the densification rate. The sintering behaviour of BaTiO 3 compacts was evaluated using both non-isothermal and isothermal experiments. Microstructural development during sintering at different heating rates was in accordance with the nonuniformity of the green compacts microstructure. Thus, denser areas could favour the development of twinned grains and the discontinuous grain growth process in the BaTiO 3 ceramics. Dielectric constants below the Curie temperature were evaluated according to both densification level and grain size. Although a high density, (⩾99% theoretical) and fine grained, (∼1.01 μm) microstructure of BaTiO 3 could be produced by the used method and sintering in air, in which a high dielectric constant, (⩾5000 at room temperature and 1 kHz) and a dissipation factor as low as 3% was achieved, however, dielectric constant degradation up to about 2500 with increasing grain size, and some fluctuations in the Curie temperature were observed. It was assumed to be a consequence of the inhomogeneous microstructure and the stresses generated through the cubic-tetragonal transition on cooling.