Effect of Nb₂O₅ Doping on Microstructures and Microwave Dielectric Loss of SrTiO₃ Ceramics

Nb-doped SrTiO₃ ceramics were prepared via sintering without extra pressure.Effects of Nb₂O₅ contents on the phase composition,microstructures and microwave dielectric loss of SrTiO₃ ceramics were investigated.Results showed that Nb₂O₅ doping has no evident impact on phase composition but hinders the densification and promotes the grain growth of samples to some extent.Upon increasing the amount of Nb₂O₅ doping,the permittivity (ε_r) of SrTiO₃ ceramics decreased from 296 to 230 and the temperature coefficient reduced from 1.714×10^-3 to 1.629×10^-3℃^-1 gradually,while the Q×f value increased sharply at first and then decreases slowly.When 0.15% (mass fraction) Nb₂O₅ were doped,the dielectric loss of SrTiO₃ ceramics was the lowest,and the Q×f reached 6 281 GHz (the dielectric constant was about 270 and the temperature coefficient 1.684×10^-3℃^-1),which is about 5.5 times as high as that of the un-doped samples (1 145 GHz). The reasons for the changes of microstructures,dielectric constants,temperature coefficients especially the dielectric loss were also discussed.