Dielectric properties of iron-containing bismuth titanate solid solutions with a layered perovskite structure

The complex oxides based on bismuth titanate with substituting iron atoms Bi$_4$Ti$_{2.98}$Fe$_{0.02}$O$_{11.99}$, Bi$_4$Ti$_{2.5}$Fe$_{0.5}$O$_{11.75}$, and Bi$_4$Ti$_2$Fe$_1$O$_{11.5}$ have been studied using dielectric spectroscopy in the frequency range from 30 to 10$^6$ Hz at a temperature of 296 K. The frequency dependences of permittivity $\varepsilon$', dielectric loss $\varepsilon$", and complex part of conductivity $\sigma$' have been studied, and the dependences $\varepsilon''(\varepsilon')$ have been constructed. The microstructure images of the studied ceramic materials have been obtained using atomic force microscopy. It has been shown that, as Fe$^{3+}$ ions are introduced as substituting atoms, there is a critical concentration $x$ (0.5 $< x <$ 1) above which the dielectric properties substantially change with variations in the number of perovskite-like layers, and the correlation is observed between the concentration of substituting Fe atoms and the grain size on the surface of the samples.