Impedance spectroscopy of dielectric properties of perovskite ceramics Bi(Mg$_{1/2}$Ti$_{1/2}$)O$_3$

The dielectric properties of metastable high-pressure perovskite ceramics Bi(Mg$_{1/2}$Ti$_{1/2}$)O$_3$ were studied by impedance spectroscopy at frequencies of 25 Hz-1 MHz at various temperatures. It is established that, at temperatures higher than $\sim$450 K, the dc conductivity makes a significant contribution to the dielectric response of these ceramics. The charge-carrier activation energy $\Delta E_{dc}$ is found from the temperature dependence of the dc conductivity $\sigma_{dc}$. As the temperature increases, the quantity $\Delta E_{dc}$ changes in a jump from 0.12 to 1.00 eV at $T\sim$ 450 K. With inclusion of the contribution from $\sigma_{dc}$, the real and imaginary parts ($M'_{ac}$ and $M''_{ac}$) of the complex electrical modulus related only to the dielectric polarization are found. From analyzing the $M''_{ac}$–$M'_{ac}$ diagrams, the contributions to the dielectric polarization from ceramic grains and their boundaries are estimated. The obtained data are interpreted in terms of the chemical composition of the ceramic compound Bi(Mg$_{1/2}$Ti$_{1/2}$)O$_3$ and the existence of crystal-lattice defects formed during the synthesis under pressure. Based on an analysis of the temperature dependences of the permittivity of ceramic grains and antiparallel displacements of the Bi$^{3+}$ cations, it is assumed that the dipole ordering in this perovskite compound is antiferroelectric in character.