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

Abstract

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. εr 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 (εr = 8.80, Qf = 33,300 GHz, and τf = −138 ppm/°C) through cold sintering of LiF powder pre-calcinated at 800 °C.