Fig. 3 shows the MW dielectric properties of the LiF ceramics as function of the processing temperatures. εr of as cold-sintered ceramics is ~6.4 and increases significantly with increasing annealing temperature until a maximum of 8.2 at 800 ◦C. The trend of εr is in good agreement with the variation of relative density, indicating that the microstructure is the dominating factor in controlling εr. According to Alford et al., the effect of porosity (P) on εr is revealed using the following equation: [23]