The dependence of the ionic conductivity σ dc ( y ) of crystallization products on the concentration is studied by impedance spectroscopy in quasi-binary systems R F 3 −PbF 2 ( R = Pr, Nd) in the region of compositions R 1 − y Pb y F 3 – y (0 ≤ y ≤ 0.22) enriched with the rare-earth component R F 3 . The single-phase tysonite (space group ) solid solutions R 1 − y Pb y F 3 – y are synthesized from the melt by directional crystallization for y < 0.1. The maximum conductivity σ dc at 296 ± 1 К is found to be 7 × 10 −5 and 3 × 10 −5 S/cm for crystals with the composition Pr 0.96 Pb 0.04 F 2.96 and Nd 0.95 Pb 0.05 F 2.95 , respectively. For 9−10 mol % PbF 2 , the samples become two-phase, the second phase—the fluorite solid solution Pb 1 − x R x F 2 + x —appears, and their ionic conductivity decreases.