Low temperature sintering of LiF-doped CoTiNb₂O₈ microwave dielectric ceramics

Rutile-structured CoTiNb₂O₈ ceramics were synthesized via traditional solid-state route. The effects of LiF addition on their sintering behavior, phase composition, microstructure and microwave dielectric properties were investigated systematically in this study. The sintering temperature was successfully lowered to 950 °C by a small amount (1 wt%) of sintering aid. XRD and EDS results indicated that chemical reaction between LiF and host ceramic took place during sintering process. And CoTiNb₂O₈ with Li_0.8Co_0.2Nb_0.96O₃ second phase coexisted in the entire composition range. The addition of LiF to the CoTiNb₂O₈ ceramics induced a limited degradation in microwave dielectric properties. The ε_r and Q × f values of the low-fired CoTiNb₂O₈ ceramics ranged from 39.4 to 53.9 and 17,580 GHz to 20,147 GHz, respectively. While the τ_f decreased in negative values with increasing LiF content. When sintered at 950 °C, the CoTiNb₂O₈ ceramic doped with 1 wt% LiF had excellent microwave dielectric properties: ε_r = 53.9, Q × f = 20,147 GHz, and τ_f = 77.2 ppm/°C, making them promising for LTCC applications.