Impedance Spectroscopy of Dielectric Properties of Perovskite Ceramics Bi(Mg1/2Ti1/2)O3

The dielectric properties of metastable high-pressure perovskite ceramics Bi(Mg1/2Ti1/2)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 similar to 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 Delta E-dc. As the temperature increases, the quantity Delta E-dc changes in a jump from 0.12 to 1.00 eV at T similar to 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(Mg1/2Ti1/2)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 Bi3+ cations, it is assumed that the dipole ordering in this perovskite compound is antiferroelectric in character.