Splitting of the transition to the antiferroelectric state in PbZr0.95Ti0.05O3 into polar and antiferrodistortive components

The phase transformations of ceramic PbZr1-xTixO3 are studied at the composition x=0.05 close to the morphotropic phase boundary between antiferroelectric orthorhombic Pbam and ferroelectric rhombohedral phases by elastic, dielectric, and x-ray diffraction measurements. Temperature scans at different rates show that the kinetics of the transition from R3m to Pbam is very sluggish, and is actually split into a slower polar component, appearing in the dielectric susceptibility and a nonpolar component, visible as a sharp stiffening of the Young's modulus. The latter is assigned to the establishment of the oxygen octahedral tilt pattern of the Pbam phase, and occurs at once at a temperature that decreases with increasing cooling rate. On heating, the transition occurs at a temperature 65 K higher than on quasistatic cooling, so that both components occur with a faster rate almost together. The Young's modulus presents a variety of apparently different types of anomalies, depending on temperature rate and history, which, however, can be well reproduced in terms of steplike anomalies corresponding to the two components of the Pbam<->R3m transition and the tilt R3c<->R3m transition in the region of coexistence of the FE and AFE phases.