Electric field gradient in LiMnFeF6 compounds. polarizable point charge calculations and Mössbauer data

The polarizable point charge model is used to explain Mössbauer data on the electric field gradient (EFG) at the iron site in α- and β-LiMnFeF₆. Lattice summations are performed in direct space. The fluorine polarizability which fits the data is in reasonable agreement with the expected value $\text{(α}{}_{\mathrm{F}}\text{～ 1.2}\text{A}\text{?}{}^3\text{)}$ The dipolar contribution is found to be important. In both cases the main EFG component is positive. In β-LiMnFeF₆, according to the structure, the EFG tensor is axial with respect to the c axis; in α-LiMnFeF₆, the asymmetry parameter η is large (?0.5) and the OZ axis is along the a axis.