Correlation between the Fluorine Ion Conductivities of Sr1 – xRxF2 + x (CaF2 Type) and R1 – ySryF3 – y (LaF3 Type) Crystals in the SrF2–RF3 Systems (R = La–Nd)

Abstract

The “conductivity logarithm–composition” correlation logσ_dc(x) = ax + b has been revealed for the strongly nonstoichiometric fluorite Sr_1 – xR_xF_2 + x (x is the RF₃ molar fraction, 0.15 ≤ x ≤ 0.47) and tysonite R_1 – ySr_yF_3 – y (y is the SrF₂ molar fraction, y = 1 – x, 0.85 ≤ x ≤ 0.97) phases in the SrF₂–RF₃ systems (R = La, Ce, Pr, Nd). The conductivity σ_dc of the eutectic 70LaF₃ + 30SrF₂ (mol %) composite fits well with the dependence logσ_dc(x) for the nonstoichiometric Sr_1 – xLa_xF_2 + x and La_1 – ySr_yF_3 – y phases.