Antiferroelectrics are essential ingredients for the widely applied piezoelectric and ferroelectric materials: the most common ferroelectric, lead zirconate titanate is an alloy of the ferroelectric lead titanate and the antiferroelectric lead zirconate. Antiferroelectrics themselves are useful in large digital displacement transducers and energy-storage capacitors. Despite their technological importance, the reason why materials become antiferroelectric has remained allusive since their first discovery. Here we report the results of a study on the lattice dynamics of the antiferroelectric lead zirconate using inelastic and diffuse X-ray scattering techniques and the Brillouin light scattering. The analysis of the results reveals that the antiferroelectric state is a ‘missed’ incommensurate phase, and that the paraelectric to antiferroelectric phase transition is driven by the softening of a single lattice mode via flexoelectric coupling. These findings resolve the mystery of the origin of antiferroelectricity in lead zirconate and suggest an approach to the treatment of complex phase transitions in ferroics.

The results of experimental studies of the crystal and domain structures of NaO, 5BiO, 5TiO₃ as well as its lattice dynamics, dielectric, optical and other physical properties are considered. Nature of peculiar temperature points is discussed.

We measured the time dependencies of the dielectric permittivity of a single crystal lead magnoniobate in the zero-field–cooled regime. The logarithmic decay of the dielectric response was observed in the glassy phase. We measured the time $\tau$ from the moment of the field application for the phase transition from the glasslike to the field-induced ferroelectric state to take place, at temperatures below 220 K. The transition is accompanied by the emerging of the even harmonics of the permittivity. It is shown that $\ln \tau$ depends linearly on both the inverse temperature and the inverse applied field strength.

Structural evolutions of PMN/PT10% $\left({\mathrm{PbMg}}_{0.3}{\mathrm{Nb}}_{0.6}{\mathrm{Ti}}_{0.1}{\mathrm{O}}_3\right)$ and PMN $\left({\mathrm{PbMg}}_{1/3}{\mathrm{Nb}}_{2/3}{\mathrm{O}}_3\right)$ are studied and compared using high-resolution x-ray and neutron diffraction. At high temperature, PMN-like diffuse scattering, associated with local disordered shifts, is evidenced by PMN/PT10%. A part of this intensity condenses at $T_c=285\mathrm{}\mathrm{K}$ when PMN/PT10% exhibits a structural phase transition toward a long-range rhombohedral phase, whereas in PMN the polar order remains short ranged. In the ferroelectric phase of PMN/PT10% local [100] displacements of lead are evidenced, and are connected to the observation of diffuse scattering far below $T_c.$ The local symmetry in which oxygen and Ti/Mg/Nb cations are shifted along the [111] direction, but in which the lead atoms are shifted along one of the tetragonal [100] directions is monoclinic. This short-range polar order reconstructs on average a polar rhombohedral symmetry. A global picture for the structural evolution in the PMN/PT compounds is proposed. It is based on competition between rhombohedral and tetragonal polar order, which connects the relaxation properties of PMN and the high piezoelectric response of morphotropic monoclinic PMN/PT with a high concentration of PT.

Peculiarities of phase transitions in disordered perovskite-like crystals—PbMg_1/3 Nb_2/3 O₃ (PMN) and Na_1/2 Bi_1/2 TiO₃ (NBT) have been studied by neutron scattering. The strong quasielastic scattering (QES) related to ferroelectric critical fluctuations has been observed instead of expected inelastic scattering of soft phonon mode. The wavevector dependence of this diffuse scattering has been well described by Ornstein-Zernice formula. The correlation length temperature dependence resembling that of spin-glasses has obtained. The history dependent effects have been found by measurements in electric field in “field cooled” (FC) and “zero field cooled” regimes. Those effects as well as long-time relaxation of Bragg peaks intensity, observed below certain temperature, clearly indicate glass-like nature of low-temperature phase.