Crystal structure and microwave dielectric properties of temperature stable (CoxZn1-x)TiNb2O8 ceramics

(CoxZn1-x)TiNb2O8 (x = 0.2-0.8) microwave dielectric ceramics were synthesized via the conventional solid-state reaction route, and the correlation of microwave dielectric properties on the crystal structure was discussed. Crystal structures of ceramic samples were systematically investigated by X-ray powder diffraction. Moreover, composition-induced phase transitions were confirmed via the following sequence: for x <= 0.2, single-phase orthorhombic ixiolite (ZnTiNb2O8) was formed, whereas for 0.3 <= x<0.8, ixiolite and rutile coexisted. When x >= 0.8, only single-phase rutile was detected. For the (CoxZn1-x)TiNb2O8 ceramics, the microwave dielectric properties were changed with the crystal structural transitions: the dielectric constant (epsilon(r)) and the temperature coefficient of resonant frequency (tau(f)) increased upon increasing the Co2+, but the quality factor (Q) decreased. A near-zero tau(f) = +1.6 ppm/degrees C was obtained in the Co0.38Zn0.62TiNb2O8 ceramics with epsilon(r) = 40.7 and high Q x f = 16 790 GHz. These research outcomes are expected to have great significance for developing microwave dielectric ceramics in practical applications.