Extreme values of relative permittivity and dielectric relaxation in Sr2SbMnO6 ceramics

Abstract

A polycrystalline ceramic of Sr2SbMnO6 (SSM) was fabricated using the powders obtained by the conventional solid-state reaction route. The dielectric measurements of the ceramic were carried out as a function of frequency (100 Hz–10 MHz) and temperature (190–360 K). SSM exhibited higher relative permittivity (∼2 × 105 for 1 kHz at 360 K) than that for the recently known high permittivity ceramic CaCu3Ti4O12 (CCTO). It decreased to a relatively low value (∼2 × 103 for 1 kHz) on decreasing the temperature down to 195 K. The modified Cole–Cole equation that included the conductivity term was used to describe the dielectric spectra of the ceramic. Impedance spectroscopy was employed to determine the electrical parameters (resistance, capacitance and relaxation time) of the grain and the grain boundary. The grain and grain boundary conduction and the dielectric relaxation time followed an Arrhenius law associated with activation energies of 0.22 eV, 0.35 eV and 0.24 eV, respectively. Nearly equal activation energies for dielectric relaxation and grain conduction revealed a possibility of invoking a common mechanism to rationalize the permittivity data. The capacitance and resistance associated with the grain boundary were found to be higher than that associated with the grain to a great extent. The incidence of giant relative permittivity and the other experimental findings support the Maxwell–Wagner type of mechanism.