Lattice Distortion around Impurity Ions in Alkali Halide Crystals I. Calculation of Lattice Distortion and Comparison with X-Ray Data of Lattice Parameter Changes

Abstract

Displacements of nearest-neighbor ions around various substitutional impurities in alkali halide crystals are calculated by the isotropic approximation and by the superlattice approximation using the repulsive potentials of Born type and Born-Verwey type. Results of these calculation agree with each other within the error of ±20%.
Lattice parameter change due to solute ions, also calculated by these methods, are compared with available experimental data. Theoretical estimates of lattice parameter changes are found to be larger than experimental values.
Possible ambiguities involved in these theories are examined, and it is concluded that Eshelby’s theory of lattice parameter change is reliable within the error of about ±20%, provided the effect of core relaxation and anisotropy of distortion is properly taken into account.