The valence of copper in sulphides and selenides: An X-ray photoelectron spectroscopy study

A number of copper sulphides and selenides were studied using X-ray photoelectron spectroscopy. It was found that the copper in all the compounds is monovalent, while the average oxidation state of the chalcogen varies from —2 in Cu2S and Cu2Se, to − 32 in Cu3Se2, to −1 in CuS and CuSe and to built− 12 in CuS2 and CuSe2. The deficit of electrons relative to a closed-shell configuration is delocalized (holes in the S(3p) or Se(4p) valence band), leading to p-type metallic conduction. This is also found for the ternary compounds KCu4S3, CuV2S4 and TlCu2Se2. S2− and S− coexist in KCu4S3; the new compounds TlCu4S3 and KCu4Se3 are isostructural with KCu4S3.