Microwave dielectric properties of ZnO–Nb2O5–xTiO2 ceramics prepared by reaction-sintering process

The ZnO–Nb2O5–xTiO2 (1 ≤ x ≤ 2) ceramics were fabricated by reaction-sintering process, and the effects of TiO2 content and sintering temperature on the crystal structure and microwave dielectric properties of the ceramics were investigated. The XRD patterns of the ceramics showed that ZnTiNb2O8 single phase was formed as x ≤ 1.6 and second phase Zn0.17Nb0.33Ti0.5O2 appeared at x ≥ 1.8. With the increase of TiO2 content and sintering temperature, the amount of the second phase Zn0.17Nb0.33Ti0.5O2 increased, resulting in the increase of dielectric constant, decrease of Q × f value, and the temperature coefficient of resonant frequency (τf) shifted to a positive value. The optimum microwave dielectric properties were obtained for ZnO–Nb2O5–2TiO2 ceramics sintered at 1075 °C for 5 h: εr = 45.3, Q × f = 23,500 GHz, τf = +4.5 ppm/°C.