Dielectric relaxation and microwave loss in the La(Mg_1/2Ti_1/2)O₃–(Na_1/2Bi_1/2)TiO₃ perovskite ceramics

Dielectric response of the perovskite ceramics (1–x)La(Mg_1/2Ti_1/2)O₃–x(Na_1/2Bi_1/2)TiO₃ [(1–x)LMT–xNBT] (0 ⩽ x ⩽ 0.6) has been characterized at radio, microwave, and far infrared frequency ranges. Temperature variations of the dielectric permittivity and loss estimated by different methods were compared and analyzed. It was revealed that the low temperature dielectric response of the compositions with x ⩾ 0.2 is frequency-dependent over a wide range (10²–10⁹ Hz) below the resonant frequencies of the polar phonon modes. Contributions of different factors (both extrinsic and intrinsic) to the microwave dielectric loss of the ceramics were considered. The dielectric relaxation has been associated with the amount of bismuth in the system. The relaxation in LMT–NBT was considered in the context of similar effects observed in other Bi-containing, A-site disordered oxygen-octahedral compositions.