Lattice Vibrations and Interatomic Forces in AIIB2IIIC4VI Defect-Chalcopyrite Compounds (II). Analysis of Nonpolar Optical Modes

A simplified version of the Keating model originally derived for defect-chalcopyrite compounds is extended to include all A^IIB₂^IIIC₄^VI compounds with ordered arrays of vacancies. It is shown that the trends and frequencies of the nonpolar optical modes of these compounds can be described within this model. Simple scaling laws for the interatomic force constants are proposed and compared with corresponding relations for other binary and ternary compounds with tetrahedral coordination.