Effect of TiO2 on phase composition and microwave dielectric properties of Zn1.01Nb2O6 ceramics

Nonstoichiometry has been playing an important role in the microwave dielectric performance of columbites A2+Nb2O6 (A2+ = Ca, Mg, or a transition metal). Herein, with an excess of 0.01 mol Zn, the Q×f values of ZnNb2O6 ceramics could be effectively improved from 121,000 GHz to 138,000 GHz. On the basis of high-Q Zn1.01Nb2O6 ceramics, TiO2 was chosen to further tune the τf values for the matrix materials prepared by the conventional solid-state reaction method. The results showed that, with the increase of TiO2 content, the ZnNb2O6-based ceramics underwent four phase regions: columbite (ZnNb2O6) solid solution, ixiolite (ZnTiNb2O8) solid solution, mixture of ZnTiNb2O8 and rutile (Zn1/3Nb2/3)0.5Ti0.5O2, and (Zn1/3Nb2/3)0.5Ti0.5O2 solid solution. Such changes in phase formation had an important influence on the microwave dielectric behavior of (1−x)Zn1.01Nb2O6-xTiO2 ceramics. Importantly, τf could be tuned from −15.3 ppm/°C to +13.9 ppm/°C along with x increased from 0.58 to 0.6. Accompanied with εr ≈ 44.64 ~ 47.43 and Q×f ≥ 12,300 GHz, these materials are promising candidates for applications in microwave components and devices.