First‐Order Raman Scattering in NiS2—xSex

The Raman spectra of the system NiS2—xSex are investigated for x = 0.00, 0.10, 0.20, 0.30, and 0.55, at room temperature and at temperatures below the point where the x = 0.55 sample suffers a resistivity change from semiconducting (T ≥ 120 K) to metallic (T ≥ 120 K). No qualitative or anomalous quantitative changes in the spectrum of the sample are found that could be associated with the anomaly in its transport properties. A mode of Ag symmetry appears in the alloys which is absent from the spectrum of pure NiS2. This mode is successfully explained in terms of vibrations of S—Se pairs. Other modes decrease in frequency with increasing selenium concentration, a trend easily understood considering the increase in the unit cell volume with increasing x.