Raman spectrum of AgGaS2

Abstract
The first- and second-order Raman spectrum of AgGaS2 has been measured at room temperature. A careful analysis of the data gives phonon frequencies for the various representations at the zone centre which differ considerably from the results of two other investigations, and reasons are given why previous determinations are probably in error. The present results indicate that AgGaS2 cannot be regarded as a small perturbation of a zincblende structure, but they are in accord with the predictions of a recent model calculation by Bettini (1974). A comparison of the optic modes for AgGaS2, CuGaS2 and CuAlS2 shows regularities which are also apparent in the analogous phosphides, and it is inferred that there is an unobserved high-frequency B1 mode in both CuAlS2 and CdSiP2.

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