Phase structure, band gap and microwave dielectric properties of Ba8Ti3Nb4−xSbxO24 ceramics

High dielectric constant and low loss ceramics in the Ba8Ti3Nb4−xSbxO24 (x=0–2) system were prepared by conventional solid-state ceramic route. As x increased from 0 to 1.5, a single phase with hexagonal 8H perovskite structure was formed and the band gap values increased from 3.38 to 3.47 eV. However, the Sb2O3 secondary phase was detected as the x reached 2. The optimum sintering temperature was reduced from 1460 to 1380 °C, the quality factors (Q×f) were effectively enhanced from 22,900 to 38,000 GHz and τf was significantly lowered from 110 ppm/°C to 2 ppm/°C, whereas the dielectric constant decreased from 49 to 35. A good combined microwave dielectric properties with εr=37.5, Q×f=38,000 GHz, τf=15 ppm/°C were obtained for x=1.5.