Enhanced microwave dielectric properties in one-step cold sintered LiF ceramics via pre-calcination treatment

Cold sintering has proven effective in densifying microwave dielectric ceramics , but the resulting properties are significantly influenced by the crystallinity of the raw powder. In this study, lithium fluoride (LiF) raw powder underwent pre-calcination at temperatures ranging from 650 °C to 800 °C for 3 h to enhance grain crystallinity. The calcined powder was then mixed with 10 wt% deionized water and cold-sintered at 150 °C under 900 MPa for 1 h to achieve dense LiF ceramics. XRD results confirmed the preservation of LiF phase composition throughout both processes. Increasing calcination temperature exhibited a positive correlation with enhanced relative density in cold-sintered ceramics, reaching up to 98.6 % at 800 °C. SEM images revealed controlled grain growth with higher calcination temperatures. ε r increased with temperature, corresponding to the variation in relative density. Significantly, Qf value experienced substantial enhancement with increasing calcination temperature, ultimately achieving optimal microwave dielectric properties ( ε r  = 8.80, Qf  = 33,300 GHz, and τ f  = −138 ppm/°C) through cold sintering of LiF powder pre-calcinated at 800 °C.