Role of Noble Metal d‐States in the Formation of the Electron Structure of Ternary Sulphides

Combined X‐ray spectroscopic and X‐ray photoelectron investigations are made of the valence electron energy spectra in the semiconducting ternary sulphides CuGaS2, AgGaS2, AgSbS2, Ag3AsS3, and CuFeS2. The main features of such spectra in the complex compounds of noble metals are shown to be governed by the resonance character of the interaction between the d‐states of noble metal and p(s)‐states of non‐metal as already observed earlier especially in binary compounds of noble metals. Its pecularities are manifesting themselves first of all by the splitting of sulphur p‐band into two components and by pushing the latter apart from the noble metal d‐band. The magnitude of this p‐band splitting increases almost linearly with the amount of copper or silver in the compound. With the use of these data for the first time the broadeningof band gap in AIBIIICVI2 ternary sulphides is explained, which occurs under substitution of copper by silver, contrary to the usual narrowing of it with the increase of the mean atomic number of a compound.