Ferroelectric phase transitions in ionic conductors based on bismuth vadanate
Ceramic solid solutions (Bi(1 - x) La (x) )(4)V(2)O(11 - z) (I), Bi(4)(V(1 - x) Fe (x) )(2)O(11 - y) (II), and (Bi(1 - x) La (x) )(4)(V(0.96)Fe(0.04))(2)O(11 - y) (III) (x = 0-0.3, step Delta x = 0.02) are prepared using solid-phase synthesis. The concentration and temperature ranges of stabilization of different polymorphic modifications, including the ranges of concentrations x corresponding to the stabilization of the ferroelectric phase, are established. It is revealed that an increase in the concentration x in the region of existence of the pseudoorthorhombic phase alpha of the solid solutions studied leads to a decrease in the transition temperature, smearing of the transition, and an increase in the width of the thermal hysteresis of the ferroelectric phase transition. The effect of compressing of the domain walls by oxygen vacancies was revealed in the samples from the region of existence of the ferroelectric alpha phase, and the effect of dielectric relaxation was detected in the samples from the region of existence of the orthorhombic phase beta.