The ir transmission of the optical phonons for the mixed crystals ZnS1–xSex and CdS1–xSex, at various concentrations of x, was studied as a function of pressure up to about 43 kbar. At all concentrations a two-mode behavior was observed. For both systems the high frequency mode exhibits a greater pressure dependence than the low frequency mode. The gap mode observed for the ZnS1–xSex mixed crystals at low concentrations of Se is found to be pressure insensitive as contrasted to the Cd1-xSex mixed crystals.
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