The results of the experimental study of the critical X-ray scattering (CS) in PbZr0.6Ti0.4O3 (PZT40) single-crystal are presented. Temperature evolution of the CS lineshape and intensity was analyzed. It is demonstrated that CS can be described in terms of the mean-field model. Temperature dependences of the peak intensity of the CS, proportional to the static susceptibility, and the correlation length of the «ferroelectric fluctuations» follow the Curie-Weiss law with the Curie temperature Tc=638 K. Obtained results confirm the second-order character of the phase transition in the PZT40.

Lead hafnate single crystals were characterized using single crystal x-ray diffraction under simultaneous application of hydrostatic pressure and high temperatures. The information on the structure of two intermediate phases, situated between antiferroelectric and paraelectric phases in the pressure-temperature phase diagram, has been obtained. The lower-temperature intermediate phase is characterized by incommensurate displacive modulations in Pb sublattice. The higher-temperature intermediate phase is characterized by oxygen framework distortion, primarily in the form of anti-phase tilts of the oxygen octahedra, which is also present in the lower-temperature intermediate phase.

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We have studied temperature-induced phase transitions in PbZrO3 thin films by X-ray diffraction. By tracing the temperature dependence of superstructure reflections we show that the onset of antiferroelectric ordering takes place highly continuously on cooling and another, presumably ferroelectric phase is present at high temperatures, between the antiferroelectric and cubic phases. To clarify the possible reason for this behavior, we have investigated the X-ray diffraction profile with momentum transfer along the normal to the film surface and carried out the relevant simulation using the formalism of scattering by inhomogeneously deformed sample. From the analysis it follows that the near-interface layer is effectively compressed along the normal to the film. We associate this observation with the presence of dislocations through which the film is relaxed. The results suggest that the reasons for the phase transition sequence modification in thin films can be associated with inhomogeneous distribution of stress and defects in the near-interface area.