Effects of LiF addition on the densification and microwave dielectric properties of LiInO2 ceramics

Abstract Low-temperature co-fired ceramics (LTCC) LiInO2 + xwt% LiF (x = 0, 1, 2, 3, 4, 5) was synthesized by a traditional solid-state reaction method. XRD, TEM, and SEM show that all specimens form a pure-phase tetragonal structure with a space group of I41/amd. The addition of LiF can effectively optimize the microstructure and improve the relative density of LiInO2 ceramics. As x value increased, the er increased from 9.6 to 13.6, Q×f increased from 39,600 GHz to 52,500 GHz, and all the specimens exhibit a positive τf value at the range of 9.6–19.1 ppm/°C. The low-er and positive τf in LiInO2 ceramics was investigated by bond valence and P–V-L chemical bond theory, indicating that it was closely related to the rattling effect of In and Li. The concentration of oxygen vacancies was studied by dielectric spectroscopy, indicating that doping LiF can compensate for the volatilization of Li during high temperature sintering. Notably, excellent microwave dielectric properties (er ~13.6, Q×f = 52,500 GHz, and τf ~ 18.1 ppm/°C) were achieved in the LiInO2 + 3 wt% LiF sintered at 890 °C.