Repulsion parameters of ions and radicals-application to perovskite structures

Abstract

The compressible ion approach to repulsion which has been shown to work well for the alkali halides (J. Phys. Chem. Solids 37, 395 (1976) ; Curr. Sci. 46, 359 (1977)) has been extended to other cubic ionic crystals. Repulsion parameters have been refined for a number of ions and radicals viz., Cu⁺, Ag⁺, Tl⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Zn²⁺, Cd²⁺, Hg²⁺, Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Sm²⁺, Eu²⁺, Yb²⁺, Pb²⁺, H^-, O^2-, S^2-, Se^2-, Te^2-, NH₄⁺, SH^-, SeH^-, BrO₃^-, ClO₃^-, ClO₄^-, CN-, NH₂^-, NO₃^-, BH₄^-, BF₄^-, SO₄^2-, NH^2-. Using these parameters, calculations have been made on the lattice spacings and compressibilities of a number of perovskite-like crystals of the form A⁺B²⁺C₃^-. The predicted values agree well with experiment. In the case of four crystals viz., LiBaF₃, LiBaH₃, LiEuH₃ and LiSrH₃, there were large discrepancies between the calculated and observed lattice spacings. When these crystals were assumed to be of the inverse perovskite structure, calculations showed good agreement with the experimental data.