Dielectric characterization of single-crystal LiF, CaF2, MgF2, BaF2, and SrF2 at microwave frequencies

The microwave dielectric properties of single-crystal LiF, CaF₂, MgF₂, BaF₂, and SrF₂, synthesized by Stockbarger melt-growth techniques, are measured using cylindrical specimens as TE_01δ dielectric resonators enclosed in a cylindrical cavity. Single-crystal permittivity and dielectric loss tangent were evaluated at fixed frequencies between 7 and 9 GHz and over a temperature range from -75 to 150°C. The real permittivities of the measured fluorides increase quasi-linearly with temperature, permitting evaluation of the thermal coefficients of permittivity. The dielectric loss tangents increase approximately linearly with frequency, so that Qf (GHz) products at room temperature for BaF₂, SrF₂, CaF₂, LiF, and MgF₂ (normal to c-axis) are 57600, 73000, 92000, 192400, and 458600, respectively. The dielectric data supports existing ion polarizabilities that are used with molar volumes and molecular additivity rules to estimate the permittivities of more complex fluorides whose values have not been experimentally determined.