Phase transformation and microwave dielectric properties of Ba4LiTa3−xSbxO12

A series of Ba4LiTa3−xSbxO12 ceramics were prepared by the conventional solid-state ceramic route. A phase transformation from hexagonal to cubic was detected with increasing Sb content. Ba4LiTa3O12-type hexagonal structure formed when x≤1.5, whereas Ba4LiSb3O12-type cubic structure appeared at x≥2. The microwave dielectric properties of the ceramics exhibited a significant dependence on the composition. The relative permittivity (εr) decreased from 28 at x=0 to 20.2 at x=3, the quality factor (Q×f) values ranged from 103,617 to 26,100 GHz and the temperature coefficient of resonant frequency (τf) changed from positive +24.1 ppm/◦C to negative −30 ppm/°C. A temperature-stable ceramic with x=1.0 was achieved with εr~25.1, Q×f~77,700 GHz and τf~-3.6 ppm/°C.