Densification behaviour, microstructure development and dielectric properties of pure BaTiO3 prepared by thermal decomposition of (Ba, Ti)-citrate polyester resins

The thermal decomposition of (Ba,Ti)-citrate polyester resin was used to prepare high purity BaTiO3 powders. After milling, uniformity was studied using both SEM observations on surfaces of the fractured green compacts, and the pore size distribution results obtained by using Hg-porosimetry. 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 was evaluated using both nonisothermal and isothermal experiments. Microstructural development during sintering at different heating rates was in accordance with the non-uniformity of the green microstructure. Thus, denser areas could favour the development of twinned grains and discontinuous grain growth process. Dielectric constants below the Curie temperature were evaluated according to both densification level and grain size. A high density (greater than or equal to 99% theoretical) and fine grained (about 1.01 micron) microstructure could be produced by sintering in air. A high dielectric constant (greater than or equal to 5000 at room temperature and 1 kHz) and a dissipation factor as low as 3% were achieved, although dielectric constant degradation up to about 2500 with increasing grain size, and some fluctuations in the Curie temperature, were observed. This is assumed to be a consequence of the inhomogeneous microstructure and the stresses generated through the cubic-tetragonal transition on cooling. 48 refs.