Evolution of structure and electrical properties during crystallization of rapidly solidified Bi4Ti3O12

Amorphous Bi4Ti3O12 was prepared by rapid solidification from the melt. Crystallization and microstructure development during heat treatment were investigated. Dielectric and ferroelectric properties were related to microstructure. The method of materials preparation led to interesting and desirable properties for amorphous and crystallized fine-grain electrical ceramics. Crystallization behavior during heat treatment was investigated by DSC, XRD, and TEM. Direct transformation to the expected crystalline phase occurred without any major intermediary steps. Transformation kinetics were determined by a variety of techniques, and the kinetic parameters were dependent on the method used. Fully crystallized material had structure and electrical properties which were dependent on the heat treatment conditions. For materials heat treated at 600 C and above, the microstructures were dense, and with a uniform fine-grain size of less than 1 micrometer. The structures had residual strain. For decreasing heat treatment temperature, a decrease in grain size was observed, with an increase in strain, and a decrease in occurrence of domains. In addition to the observations for microstrain and domains, features of the dielectric anomaly at the Curie temperature implied increasing internal stress for materials heat treated at lower temperature. Ferroelectric hysteresis was observed for fully crystallized material. However, saturation was not possible for materials which were heat treated at 600 C and below. Coercive fields for fine-grain material were higher than for single crystal material, and materials with smaller grain sizes had higher coercive fields.