Bulk and Local Elastic Constants of Imperfect Crystals

Abstract

The influence of point defects on the elastic properties of crystals is investigated by means of the $T$-matrix method. Both bulk and local elastic constants are expressed in terms of the local changes of central and noncentral force constants. The local elastic constants are also obtained by means of a simple phenomenological model. Numerical applications are given for the $F$ center and some weakly bound impurities in alkali halides. The stress coefficients for either ultraviolet or infrared absorbtion bands as corrected for local strain effects are reported.