Influences of Al₂O3/Nb₂O₅ co-doping on structural evolution and dielectric properties of Zn_0.5Ti_0.5-x(Al_0.75Nb_0.35)_xNbO₄ (0 ≤ x ≤ 0.3) ceramics

In present study, the influences of Al₂O₃ and Nb₂O₅ co-doping for Ti site on structure and microwave dielectric performances of Zn_0.5Ti_0.5-x(Al_0.75Nb_0.35)_xNbO₄ ceramics were discussed. Pure ixiolite-structured Zn_0.5Ti_0.5NbO₄ solid solution is prepared when x ≤ 0.15. Phase transformation takes place at 0.2 ≤ x ≤ 0.3, where columbite ZnNb₂O₆ phase exists. The dielectric constant (_r) of ceramics presents a decline trend, which is attributed to the decrease of dielectric polarizability (0 ≤ x ≤ 0.15) and the formation of ZnNb₂O₆ phase (0.2 ≤ x ≤ 0.3). The quality factor (Q × f), however, decrease till x = 0.15 and increase after that. The temperature coefficient of resonant frequency (τ_f) value varies consistently with the densification. Typical dielectric ceramics (x = 0.3) was synthesized at 115°C: a _r of 25.79, a Q × f about 56114 GHz and a τ_f of -78.18 ppm/°C, were obtained.