The kinetics of the induced phase transition in single-crystal relaxor solid solutions PbMg1/3Nb2/3O3-29PbTiO3 and PbZn1/3Nb2/3O3-9PbTiO3 is studied when an electric field is applied along the [001] direction. At temperatures below the temperature of the morphotropic phase transition, the changes in the dielectric constant and optical transmission in electric fields are studied. It is shown that the decrease in optical transmission with time is associated only with a change in the sizes of nanoregions during the phase transition. It was found that the induced phase transition proceeds differently in these crystals. In PMN-29PT crystals, the formation of ferroelectric phases and the rapid establishment of macroscopic polarization are preceded by a certain delay time, while in PZN-9PT crystals, the ferroelectric phase is induced immediately after the application of the field without a delay time. The results obtained are explained by the different structures of the low-temperature phases in these compounds. Keywords: ferroelectricity, relaxors, induced phase transition.

Cadmium niobate Cd2Nb2O7 is a rare example of a bulk ferroelectric with a pyrochlore structure, which is characterized by an extremely complex phase diagram and contradictions in the structural phase transitions and polar states. Here, the dielectric spectroscopy studies of the Cd2Nb2O7 single crystals were performed. For the first time it was shown that dielectric behavior of these crystals demonstrates all typical features of the domainwall "freezing" dynamics such as the characteristic "kink" on the temperature dependence of the real part of the dielectric permittivity as well as the fulfillment of the Vogel-Tammann-Fulcher relation of the experimentally determined temperature dependence of the relaxation time. It was found that the contribution of the domainwall relaxation process to the total low-frequency dielectric permittivity is more than 85% at the temperature at which the dielectric dispersion is most pronounced. Thus, a limited family of the ferroelectrics exhibiting domain-wall freezing phenomena was expanded.

The dielectric and optical properties, as well as the time dependences of the permittivity in an electric field applied along the [001] direction, are studied in Na 1/2 Bi 1/2 TiO 3 -5 %BaTiO 3 single crystals lying near the morphotropic phase boundary. It is shown that, even in the absence of an electric field, dielectric and optical hysteresis associated with the coexistence of tetragonal and rhombohedral phases is observed in a wide temperature range, and the relative volume fractions of the two phases largely depend on temperature. It was found that at temperatures below the temperature of the morphotropic phase transition, the induction of the ferroelectric phase occurs without a delay time, which distinguishes the samples under study from PbMg 1/3 Nb 2/3 O 3 -xPbTiO 3 solid solutions. The results obtained are explained by different sizes of polar nanoregions in the low-temperature phase. Keywords: ferroelectricity, relaxors, induced phase transition.

The relationship between the temperatures of depolarization (Td) and morphotropic phase transition (TF-R) in crystalline relaxor solid solutions of various types, such as PbMg1/3Nb2/3O3-29PbTiO3 (PMN-29PT), PbZn1/3Nb2/3O3-9PbTiO3 (PZN-9PT) and NaBi1/2Ti1/2O3-xBaTiO3 (x=5,7.5%) (NBT-xBT) has been studied. For this purpose, dielectric measurements of polarized samples were carried out, and the process of induction of the ferroelectric phase in an electric field applied below the TF-R temperature was also studied. It was found that the structure of the low-temperature phases in these compounds is different, which leads to significant differences not only in the induction of the ferroelectric phase, but also to different relative positions of the temperatures Td and TF-R. In PMN-29PT, the formation of ferroelectric phases is preceded by some delay time, which is one of the hallmarks of a non-ergodic glassy phase, and in this case the temperatures Td and TF-R coincide. In PZN-9PT and NBT-5BT, the ferroelectric phase is induced immediately after the field is applied without a delay time, which indicates that below the TF-R temperature, the non-ergodic glassy phase does not appear, and the temperatures Td and TF-R do not coincide in them. The results obtained are discussed from the point of view of different degrees of diffuseness of the phase transition and different sizes of the polar regions. It is suggested that the coincidence of temperatures Td and TF-R is a consequence of the non-ergodic glassy phase and the small sizes of the polar regions. Keywords: relaxors, phase transitions, degree of smearing, depolarization temperature.

Time dependences of permittivity and optical transmission in the Pb(Mg 1/3 Nb 2/3 )O 3 –x Pb(Zr 0 . 53 Ti 0 . 47 )O 3 ( x = 16, 23, and 33%) transparent ferroelectric ceramics are studied in the electric fields of 0 < E < 6 kV/cm. It is shown that even in fields, which are less than the coercive field, a sharp decrease in the permittivity occurs in compounds with x equal to 16 and 23% in a short time, while these changes in the ceramics with x = 33% are significantly smaller and occur over a longer time. It is found that the stability of the phase induced in the field after its switching-off significantly depends on the composition of studied ceramics: the higher the x value is, the more stable the induced phase. The observed difference in the time dependences of permittivity and stability of the induced phase in ceramics with different composition is explained by different sizes of ferroelectric domains.

Some results of studying the dielectric and electromechanical properties of ceramic 16BiScO3–42PbMg1/3Nb2/3O3–42PbTiO3 relaxor ferroelectric samples in electrical fields (0 < E < 20 kV/cm) are presented. An appreciable decrease in the dielectric permittivity with time, and the disappearance of hysteresis in the dependence of the longitudinal strain on the electrical field intensity were revealed in the fields exceeding the coercive field (E > 10 kV/cm) and explained by the induced ferroelectric phase transition. The field-induced phase (presumably, tetragonal) was shown to be unstable and partially ordered. A nonmonotonical character demonstrated by the dielectric permittivity–time dependences of the studied ceramics unlike the other relaxor ferroelectrics was explained by the coexistence of glassy and ferroelectric phases.

AbstractSome results of studying the dielectric and electromechanical properties of ceramic 16BiScO_3–42PbMg_1/3Nb_2/3O_3–42PbTiO_3 relaxor ferroelectric samples in electrical fields (0 < E < 20 kV/cm) are presented. An appreciable decrease in the dielectric permittivity with time, and the disappearance of hysteresis in the dependence of the longitudinal strain on the electrical field intensity were revealed in the fields exceeding the coercive field ( E > 10 kV/cm) and explained by the induced ferroelectric phase transition. The field-induced phase (presumably, tetragonal) was shown to be unstable and partially ordered. A nonmonotonical character demonstrated by the dielectric permittivity–time dependences of the studied ceramics unlike the other relaxor ferroelectrics was explained by the coexistence of glassy and ferroelectric phases.

Some results of studying the dielectric and electromechanical properties of ceramic 16BiScO 3 –42PbMg 1/3 Nb 2/3 O 3 –42PbTiO 3 relaxor ferroelectric samples in electrical fields (0 < E < 20 kV/cm) are presented. An appreciable decrease in the dielectric permittivity with time, and the disappearance of hysteresis in the dependence of the longitudinal strain on the electrical field intensity were revealed in the fields exceeding the coercive field ( E > 10 kV/cm) and explained by the induced ferroelectric phase transition. The field-induced phase (presumably, tetragonal) was shown to be unstable and partially ordered. A nonmonotonical character demonstrated by the dielectric permittivity–time dependences of the studied ceramics unlike the other relaxor ferroelectrics was explained by the coexistence of glassy and ferroelectric phases.