Ferroelectricity

Influence of the degree of phase transition diffuseness on the depolarization temperature in relaxors of different types

L. S. Kamzina

Ioffe Institute, St. Petersburg, Russia

Abstract: The relationship between the temperatures of depolarization $(T_d)$ and morphotropic phase transition $(T_{\mathrm{F}-\mathrm{R}})$ in crystalline relaxor solid solutions of various types, such as PbMg$_{1/3}$Nb$_{2/3}$O$_3$–29PbTiO$_3$ (PMN–29PT), PbZn$_{1/3}$Nb$_{2/3}$O$_3$–9PbTiO$_3$ (PZN–9PT) and NaBi$_{1/2}$Ti$_{1/2}$O$_{3-x}$BaTiO$_3$ ($x$ = 5,7.5%) (NBT–$x$BT) 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 $T_{\mathrm{F}-\mathrm{R}}$ 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 $T_d$ and $T_{\mathrm{F}-\mathrm{R}}$. 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 $T_d$ and $T_{\mathrm{F}-\mathrm{R}}$ 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 $T_{\mathrm{F}-\mathrm{R}}$ temperature, the non-ergodic glassy phase does not appear, and the temperatures $T_d$ and $T_{\mathrm{F}-\mathrm{R}}$ 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 $T_d$ and $T_{\mathrm{F}-\mathrm{R}}$ 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.

Received: 05.07.2022
Revised: 05.07.2022
Accepted: 06.07.2022

DOI: 10.21883/FTT.2022.11.53335.422

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