Investigation On Zno-Nb₂O₅-based Microwave Dielectric Ceramics With Moderate Permitivity

The crystal structure and microwave dielectric properties of ZnO-Nb₂O₅-basedmicrowave dielectric ceramics with moderate permittivity were investigatedsystematically. Different additives were doped into the ZnO-Nb₂O₅-based ceramics,based on the theory of bond valence and solid solution’s enhancement, to improve themicrowave dielectric properties of the system. Further, the addition of TiO₂wasemployed to improve the temperature coefficient of resonant frequency. TheZnO-Nb₂O₅-based microwave dielectric ceramics with high Qf value and excellenttemperature stability were prepared by the conventional solid-state solution.Thecrystal structure was analyzed by Rietveld refinement method. The relationshipsbetween crystal structure and microwave dielectric properties were discussed.Firstly, the microwave dielectric properties and crystal structure ofZn0.9Ti0.8-xSnxNb2.2O8（x=0.00,0.05,0.10,0.15） ceramics were investigated.According to the theory that the temperature coefficient of resonant frequency （τf） canbe improved by increasing the bond valence, we increased the content of Nb anddoped Sn which has large bond valence parameter into the system to moderate thetemperature stability of ZnTiNb2O8. The addition of SnO2improved the temperaturecoefficient of resonant frequency, decreased the dielectric polarizability, packingfraction and grain size. This lead to the decrease of dielectric constant and Qf value.Secondly, the influences of MgO and NiO addition on microwave dielectricproperties of ZnTiNb2O8ceramic were studied systematically. The relationshipsbetween microstructure and microwave dielectric properties were discussed byinvestigating the influence of MgO and NiO addition on microstructure andmicrowave dielectric properties of Zn1-xMgxTiNb2O8（x=0.10,0.20,0.30,0.40）ceramics and Zn1-xNixTiNb2O8（x=0.10,0.20,0.30,0.40） ceramics.Finally, in order to improve the temperature stability further, TiO₂was added tothe system since it own positive and large temperature coefficient of resonantfrequency. The influences of TiO₂addition on the mechanism of microwave dielectricproperties’ improvement were interpreted by analyzing the influences of TiO₂on thecrystal structure of Zn0.8Ni0.2TiNb2O8ceramics and ZnZrNb2O8ceramics.