Zone‐centered phonons in ternary compounds of chalcopyrite structure

A Keating model calculation of the zone‐centered phonons in ternary compounds of the chalcopyrite (ch) structure is presented. The calculations are restricted to phonons of the phosphor(P) ch‐family. The model describes reasonalby well the phonons of high energy. The spectra are determined preponderantly by the masses of the cations and the force constants between nearest neighbours. The influence of the force constants between second nearest neighbours and the effective charges is small. The dependence of the individual phonons upon changes in the model parameters is unravelled. The variation of the ir‐oscillator strength of the same mode in different compounds demonstrates the importance of changes in the eigenvectors. The force constants of the chalcopyrite (ch) bonds are compared to those of corresponding zincblende (zb) bonds and can be explained by changes in the bond length. The model calculations yield a symmetry assignment of the experimental spectra in CdSnP2 and ZnSnP2.