Zone center frequencies of tetragonal CdAl2Se4

A short-range force constant and a modified rigid ion model have been appli ed for the first time to investigate the phonons in the CdAl2Se4 defect cha lcopyrite compound in its tetragonal phase. The calculation with one bendin g and six stretching force constants in the short-range force constant mode l agrees well with the observed Raman and infrared frequencies. The Al-Se i nteratomic force constants of its bonds are found to be stronger than the C d-Se interatomic force constants. In the modified rigid ion model, the effe ctive charges have been incorporated along with the stretching and the bend ing force constants to exhibit a good agreement for the observed Raman and infrared frequencies. The effective charge on Cd cation has been found to b e much smaller than the effective charge on Al cation. (C) 2000 Academic Pr ess.