Structure and dielectric properties of solid solutions Bi$_{7}$Ti$_{4+x}$W$_{x}$Ta$_{1-2x}$O$_{21}$ ($x$ = 0–0.5)

A number of solid solutions Bi$_{7}$Ti$_{4+x}$W$_{x}$Ta$_{1-2x}$O$_{21}$ ($x$ = 0–0.5) have been synthesized from oxides by solid-phase reaction. The crystal structure, the electrophysical characteristics, and the microstructure of the prepared ceramic samples have been studied. According to X-ray powder diffraction, all the compounds are single-phase with the structure of mixed-layer Aurivillius phases ($m$ = 2.5) with the orthorhombic crystal lattice (space group $I$2$cm$, $Z$ = 2). Temperature dependences of the relative permittivity $\varepsilon(T)$ of the compound have been measured, from which it has been found that the Curie temperature $T_C$ of perovskite-like oxides Bi$_{7}$Ti$_{4+x}$W$_{x}$Ta$_{1-2x}$O$_{21}$ ($x$ = 0–0.5) decreases linearly as substitution parameter x decreases. The activation energies of charge carriers have been found in different temperature ranges.