Theory of Crystalline Fields of Iron-Group Ions in Solid Solutions

Abstract

A method for calculating lattice distortions in solid solutions developed in earlier work on alkali halide solid solutions is applied to the case of iron-group ions, ${\mathrm{Mn}}^{3+}$, ${\mathrm{Co}}^{++}$, ${\mathrm{Ni}}^{++}$, ${\mathrm{Fe}}^{3+}$, and ${\mathrm{Cr}}^{3+}$, dissolved in alkaline-earth oxides MgO, CaO, BaO, and SrO. The cubic potential at the solute-ion site is calculated in the distorted lattice and compared with the corresponding potential in the undistorted host lattice. The trends in the calculated cubic potential with differences in ionic radii and charges are found to be in qualitative agreement with experimental trends. In a few cases where the cubic field splitting is available, a consideration of the lattice distortion improves agreement with experiment. To improve quantitative agreement between experiment and theoretically calculated crystal-field parameters, one would, of course, have to consider electronic overlap and covalent effects, but our results give definite indications that lattice-distortion effects also play a significant role.