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 o f the maximum dielectric constant was shifted to a lower temperature with a decrease in measurement frequency with increasing A-site vacancy concentra tions. 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 10(14) s(-1) were determined. No frequency disp ersion in the imaginary part of the permittivity was found below the temper ature of the dielectric maximum. A linear polarization-electric field depen dence was observed at room temperature. A polarization of 0.3 mu C/cm(2) wa s found under a field of 75 kV/cm at 25 degrees C. Phase analysis revealed a single phase perovskite structure with a hexagonal unit cell with a=5.77 Angstrom and c=7.08 Angstrom. < 110 > selected area electron diffraction pa tterns 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. (C) 2000 American Institute of Physics. [S00 21-8979(00)09017-4].