IN-SITU X-RAY-DIFFRACTION STUDY OF CRYSTALLIZATION KINETICS IN PBZR1-XTIXO3 (PZT, X=0.0, 0.55, 1.0)

The crystallization of PbZr1-xTixO3, x = 0 (PT), 0.55 (PZT), and 1.0 (PZ), from alkoxide gels, in air, has been studied by in situ by X-ray powder diffractometry at temperatures in the range 380-500-degrees-C. Prior to crystallization, an intermediate fluorite or pyrochlore phase is observed for PZ and PZT but not for PT. This is consistent with zirconium enhancing the likelihood of fluorite phases. The results demonstrate that the crystallization temperatures increase in the sequence PT < PZ < PZT. However, on a homologous temperature scale (T/T(melting)) the crystallization temperature for PT and PZ are both approximately 0.41T(melting) and for PZT the crystallization temperature is approximately 0.46T(melting). Crystallization at lower temperatures is preceded with an induction period which reflects the time necessary to establish a steady-state population of embryos. The crystallization kinetics were monitored by following the integrated intensity of the (200)cubic perovskite peak with time. Quantitative analysis of the Bragg peak full widths at half-maximum show that the crystallite size saturates to a constant value during crystallization. The value of the saturated particle size increases with increasing crystallization temperature, indicating that the final particle sizes are dictated nucleation rates. These results are placed in the context of an Avrami analysis of the transformation kinetics.