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 ′ m around 200–330 °C, and the dielectric constant ɛ′ varies from several hundreds at 20 °C to about two thousands of ε ′ 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.