Antiferroelectric and ferroelectric phase transitions of the displacive and order-disorder type in PbZrO3 and PbZr1-xTixO3 single crystals

For PbZrO3 and PbZr0.99Ti0.01O3 single crystals the first order Raman light scattering spectra in the paraelectric phase have been analysed. In lead z irconate two kinds of crystals, with and without a transient phase, were in vestigated. It was found that temperature dependence of the defect-induced soft mode frequency in the paraelectric phase has a negligible contribution to the low-frequency dielectric response. From the point of view of strong dielectric relaxation in the range of 10(6)-10(9) Hz, which originates in a disorder of the lead sites, crossover of the order-disorder and displaciv e type of antiferroelectric phase transition in lead zirconate is considere d: the phase transition mechanism is neither purely displacive nor order- d isorder. Contribution of physical phenomena responsible for the epsilon(ome ga, T) dielectric response at low frequencies of an external electric field are described.