Dielectric properties of new perovskite ceramics (Na1/4Bi3/4)(Mg1/4Ti3/4)O3 and (K1/4Bi3/4)(Mg1/4Ti3/4)O3

New perovskite ceramics (Na1/4Bi3/4)(Mg1/4Ti3/4)O3 (NBMT) and (K1/4Bi3/4)(Mg1/4Ti3/4)O3 (KBMT) were synthesized using solid-state reaction method. These two new ceramics have cubic symmetry structure at room temperature. Both NBMT and KBMT show a frequency-dependent broad dielectric maximum ε′mε′m around 200–330 °C, and the dielectric constant ɛ′ varies from several hundreds at 20 °C to about two thousands of ε′mε′m. No ferroelectric behaviour is observed. Between 102 and 106 Hz, the ɛ′ exhibits frequency dispersion in rather wide temperature range. The frequency dependence of ɛ′ follows the formula, ɛ′(ν) = ɛ′(1 Hz) − B log ν, at low temperature side of the Tm.