Dielectric Properties of Ba0.8Ca0.2TiO3-Bi(Mg-0.5, Ti-0.5)O-3-NaNbO3 Ceramics

Ceramics in the solid solution system, (1-x)Ba0.8Ca0.2TiO3-xBi(Mg0.5Ti0.5)O3, were prepared by a conventional mixed oxide route. Single phase perovskite-type x-ray diffraction patterns were observed for compositions x < 0.6. A change from tetragonal to single-phase cubic x-ray patterns occurred at x ≥ 0.1. Dielectric measurements indicated relaxor behaviour for x ≥ 0.1. Increasing the Bi(Mg0.5Ti0.5)O3 content improved the temperature-sensitivity of relative permittivity εr at high temperatures. At x = 0.5, a near plateau relative permittivity, 835 ± 40, extended across the temperature range, 65 °C to 550 °C; the permittivity increased at x = 0.6 to 2170 ± 100 for temperatures 160 °C to 400 °C (1 kHz). The corresponding loss tangent, tanδ, was ≤ 0.025 for temperatures between 100 °C and 430 °C for composition x = 0.5; at x = 0.6, losses increased sharply at > 300 °C. Comparisons of dielectric properties with other materials proposed for high temperature capacitor applications suggests that (1-x)Ba0.8Ca0.2TiO3-xBi(Mg0.5Ti0.5)O3 ceramics are a promising base material for further development.