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Ferroelectricity

Dielectric properties of solid solutions $(1-x)$(KBi)$_{1/2}$TiO$_3$–$x$Na$_{1/4}$Bi$_{3/4}$Fe$_{1/2}$Ti$_{1/2}$O$_3$ near the morphotropic phase boundary

Yu. V. Radyush, N. M. Olekhnovich, A. V. Pushkarev

Scientific-Practical Materials Research Centre of NAS of Belarus

Abstract: The dielectric properties of solid solution ceramics $(1-x)$(KBi)$_{1/2}$TiO$_3$–$x$Na$_{1/4}$Bi$_{3/4}$Fe$_{1/2}$Ti$_{1/2}$O$_3$ near the morphotropic phase boundary lying near $x$ = 0.75 and separating the compositions with the orthorhombic ($x <$ 0.75) and rhombohedral ($x >$ 0.75) structures have been studied. The solid solutions are shown to undergo a diffuse phase transition with the Curie temperature $T_{\mathrm{C}}$ = 640–650 K. Based on an analysis of the frequency dependence of the imaginary component of the electric modulus in the range $T>T_{\mathrm{C}}$, it is concluded that the transition of the system of solid solutions near the morphotropic phase boundary ($x$ = 0.75) to the dipole-ordered state is accompanied by the formation of heterophase microregions with different relaxation times of the dielectric polarization. The activation energies of the relaxation of the dielectric polarization $(\Delta E_M)$ in the aforementioned temperature range and of the dc charge carriers $(\Delta E_{dc})$ are determined. It is found that $\Delta E_{dc}$ stepwise increases near 570 K in going toward higher temperatures. It is shown that the behavior of the characteristics of the dielectric response of the solid solutions below 400 K corresponds to a relaxor ferroelectric. For the compositions 0.7 $\le x\le$ 0.8, the estimated freezing temperature of dipole clusters of the relaxation state is about 240 K, and their activation energy decreases with increasing $x$.

Received: 14.04.2011
Accepted: 27.06.2011

 English version: Physics of the Solid State, 2012, 54:1, 91–97

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