Calculation of the shape of the potential well ofMn2+in CaO, SrO, and BaO

Abstract

The shape of the potential energy well of ${\mathrm{Mn}}^{2+}$ as impurity in a number of alkaline-earth oxides is calculated, using the method of Hatcher and Dienes, for a polarizable-point-ion model. Potentials for the Mn-O, Ca-O, Sr-O, and Ba-O repulsion are derived. It is found that an effective charge of $Z=1.6$ on the ions yields results that are in agreement with experiment. In CaO the ${\mathrm{Mn}}^{2+}$ ion occupies a substitutional site. In SrO the site of ${\mathrm{Mn}}^{2+}$ is also substitutional, but the potential well is very flat over a distance of 0.3 \AA{} in the $〈111〉$ direction. BaO: ${\mathrm{Mn}}^{2+}$ is found to be an off-center system. The off-center sites in the $〈111〉$ and $〈110〉$ direction are both 0.5 eV in energy below the ideal lattice site. The displacements of the impurity in the $〈111〉$ and $〈110〉$ directions are 0.6 and 0.8 \AA{}, respectively.