Study of Pb0.5Cd0.25Lu0.25F2.25 Fluorite Solid Solution with Congruent Melting Nature

The optical, mechanical, and conductive properties of the Pb_0.5Cd_0.25Lu_0.25F_2.25 crystal host have been studied for the first time in comparison with the crystals of the initial single-component fluorides. The short-wavelength transparency cut-off of the three-component mixed crystal is determined by the presence of PbF₂ in its composition; the IR limit is naturally shifted to 15 µm due to the presence of LuF₃ in the composition. The refractive index of the studied solid solution, n = 1.6889 at the wavelength λ = 0.6328 µm, is lower than that of the PbF₂ crystal due to the introduction of less polarizable components CdF₂ and LuF₃. Significant hardening is observed for the three-component crystal: the microhardness H_V = 2.5 GPa, which exceeds the hardness values for PbF₂ and CdF₂ by almost 40%. The electrical conductivity σ_dc of Pb_0.5Cd_0.25Lu_0.25F_2.25 at 500 K is 5.5 × 10⁻⁵ S/cm, which corresponds to the conductivity level of solid solutions M\(_{{1 - x}}\)Lu_xF\(_{{2 + x}}\) (M = Ca, Sr, Ba). The studied multicomponent fluoride material can be a promising crystal medium for various photonic applications.