Relaxational polarization in polar dielectric barium magnesium niobate

Relaxor-like dielectric behavior, analogous to that found in lead magnesium niobate, has been induced in the polar dielectric barium magnesium niobate (BMN). In BMN, the dielectric constant was increased and the temperature of the maximum dielectric constant was shifted to a lower temperature with a decrease in measurement frequency with increasing A-site vacancy concentrations. The frequency dispersion of the permittivity maximum exhibited good agreement with the Arrhenius relationship. An activation energy of 0.15 eV and a preexponential factor 1014 s−1 were determined. No frequency dispersion in the imaginary part of the permittivity was found below the temperature of the dielectric maximum. A linear polarization-electric field dependence was observed at room temperature. A polarization of 0.3 μC/cm2 was found under a field of 75 kV/cm at 25 °C. Phase analysis revealed a single phase perovskite structure with a hexagonal unit cell with a=5.77 Å and c=7.08 Å. 〈110〉 selected area electron diffraction patterns revealed superlattice reflections along the 〈111〉. High resolution Z-contrast imaging was used to study the local ordering and the origin of the relaxational polarization.