Mn2+impurities in fluoroperovskites: a test for theoretical calculations

The equilibrium impurity-ligand distance, R e , in six fluoroperovskites of the AMF 3 series (A: K, Rb, Cs; M: Mg, Zn, Cd, Ca) doped with Mn 2+ has been explored through density functional calculations for MnF 6 A 8 M 6 16+ clusters where the effects of the electrostatic potential due to the rest of the lattice are included. The R e -values obtained coincide, within the experimental uncertainties, with those derived from the analysis of the experimental isotropic superhyperfine constant, A s , and the 10 Dq -parameter and also with available extended x-ray absorption fine-structure results. This important result is shown to be practically independent of the quality of the basis set employed. From the analysis of recent electron paramagnetic resonance data for AlF 3 :Mn 2+ it is concluded that, for this system, R e 197 pm which is 7% smaller than the average distance for pure compounds involving MnF 6 4- complexes. The latter figure is shown to be consistent with the substitution of Mn 2+ for a trivalent cation in AlF 3 :Mn 2+ . The present theoretical scheme has also been applied to Tl + impurities in NaI. First results indicate an outwards relaxation of ligands which is equal to, at least, 5% and thus is much higher than the figure (1%) calculated by Aguado et al (Aguado A, Ayuela A, Lopez J M and Alonso J A 1998 Phys. Rev. B 58 11 964).