Chemical substitution in spinel structured LiZnNbO4 and its effects on the crystal structure and microwave performance

LiZn1-xMxNbO4 (M = Co, Ni) (x = 0-0.06) systems were fabricated by a facile solid-state reaction method. Structure and property relationships of spinel structured LiZn1-xMxNbO4 were investigated systematically. Appropriate amount of Co2+ and Ni2+ greatly improved the dielectric loss of LiZnNbO4 ceramics. While, the dielectric loss deteriorated seriously when the doping content exceeded x = 0.02. The origin of dielectric loss in LiZn1-xMxNbO4 ceramics was investigated systematically. Moreover, the theoretical dielectric constant and linear expansion coefficient were calculated on the bases of the crystallographic parameters from XRD refinement. The temperature coefficient of resonant frequency calculated by the P-V theory agreed well with the test values. Due to the small doping content, the change in chemical bonds was negligible. Density became the major factor determining the variation of dielectric constant in LiZnNbO4 ceramics. At last, excellent microwave dielectric properties were obtained: Ts = 1010 °C, εr = 15.25, Qf = 107,000 GHz, τf = −63.3  ppm/°C for LiZn0.98Co0.02NbO4 and Ts = 995 °C, εr = 14.85, Qf = 104,000 GHz, τf = −61.7  ppm/°C for LiZn0.98Ni0.02NbO4.