Effects of CaF2 addition on the microstructure and microwave dielectric properties of ZnNb2O6 ceramics

The effects of CaF2 additions on the microstructure and the microwave dielectric properties of ZnNb2O6 ceramics were investigated systematically. The sintering temperature of ZnNb2O6 ceramics with 0.5 wt.% CaF2 additions can be effectively reduced from 1150 °C to 1080 °C. The secondary phase CaNb2O6 was observed in sintered samples with 1–5 wt.% CaF2 additions. There was evidence of reaction between CaF2 and ZnNb2O6 during sintering. The dielectric properties at microwave frequencies (6–8 GHz) in this system were strongly dependent on the relative density, sintering temperature and CaF2 content. For 0.1–5 wt.%-CaF2-doped ZnNb2O6 ceramics, The dielectric constants (εr) of densified samples range in 28–31 which is higher than that of undoped ZnNb2O6 ceramics, However, the Q×f values decreased and ranged from 39000 GHz to 68000 GHz. The τf values were shifted toward zero direction with the increase of CaF2 addition. ZnNb2O6 ceramics with 0.5 wt.% CaF2 addition sintered at 1080 °C have the optimum microwave dielectric properties: εr=32, Q×f=68 000 GHz and τf=−55 ppm/°C.