Role of Ca2+ in the change in the structure type and the fluoride-ion conductivity in crystals upon transition from β-ErF3 to Er0.715Ca0.285F2.715

Abstract

The symmetry dependent structural differences and the fluoride ion conductivity of the β ErF 3 crystal (the orthorhombic β YF 3 type) and the phase Er 0.715 Ca 0.285 F 2.715 (the hexagonal tysonite modifica tion α LaF 3 ) are revealed. A change in the β YF 3 structure type is caused by the partial replacement of Er 3+ by Ca 2+ . It was shown that the contribution of Ca 2+ to the conductivity of the phases R 1 ⎯ y Ca y F 3 ⎯ y is not lim ited to the creation of V anion vacancies. The crystals of Er 0.715 Ca 0.285 F 2.715 characterized by cation com position heterogeneity have structural features (different from the vacancies in the anionic sublattice), which can exert a positive effect on the mobility of fluoride anions. This factor may play a more important role in ion transport than the concentration of anion vacancies.