Crystal-Field Studies ofFe2+by the Mössbauer Effect: FeF2

Mössbauer experiments on Fe${\mathrm{F}}_2$ in the paramagnetic state are reported. The temperature dependence of the quadrupole splitting is studied experimentally, and interpreted in terms of the variations with temperature of the populations of the energy levels of the ferrous ion. From this analysis, values for the crystal-field splittings of the $T_{2g}$ orbital levels of the ${\mathrm{Fe}}^{2+}$ ion are extracted. The best fit with experiment is obtained for $E_2-E_1=1150\mathrm{}°$K, $E_3-E_1=1300\mathrm{}°$K, with a certain spread in the acceptable values for these energy separations. The results agree well with values deduced previously by magnetic and optical techniques. It is shown, however, that all these results, though consistent among themselves, cannot be explained in terms of a conventional crystalline potential.