Degree of dynamical charge overlap in ionic crystals

Abstract

The degree of dynamical charge overlap in Sr${\mathrm{Cl}}_{2}$:${\mathrm{Sm}}^{2+}$ relative to that in Sr${\mathrm{F}}_{2}$:${\mathrm{Sm}}^{2+}$ has been determined from vibronic and static stress data and is compared with theoretical results obtained from a classical, extended-charge shell model. The results definitely imply that there exists less charge overlap in Sr${\mathrm{Cl}}_{2}$ than in Sr${\mathrm{F}}_{2}$. An analysis based on the extended-charge shell model indicates that the major source of this result is the high electronic polarizability of the ${\mathrm{Cl}}^{\ensuremath{-}}$ ion compared to the ${\mathrm{F}}^{\ensuremath{-}}$ ion. Apparently, the electronic charge distribution of the ${\mathrm{Cl}}^{\ensuremath{-}}$ ion distorts within its own ionic volume rather than penetrates into the charge distribution of its neighbor. The opposite appears to be the case for the ${\mathrm{F}}^{\ensuremath{-}}$ ion.