Electronic structure of lanthanum copper oxychalcogenides LaCuOCh (Ch=S, Se, Te) by X-ray photoelectron and absorption spectroscopy

X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge spectroscopy (XANES) have been applied to examine the electronic structures of lanthanum copper oxychalcogenides LaCuOCh (Ch=S, Se, Te), whose structure has been conventionally viewed as consisting of nominally isolated [LaO] and [CuCh] layers. However, there is evidence for weak La–Ch interactions between these layers, as seen in small changes in the satellite intensity of the La 3d XPS spectra as the chalcogen is changed and as supported by band structure calculations. The O 1s and Cu 2p XPS spectra are insensitive to chalcogen substitution. Lineshapes in the Cu 2p XPS spectra and fine-structure in the Cu L- and M-edge XANES spectra support the presence of Cu+ species. The Ch XPS spectra show negative BE shifts relative to the elemental chalcogen, indicative of anionic species; these shifts correlate well with greater difference in electronegativity between the Cu and Ch atoms, provided that an intermediate electronegativity is chosen for Se.

The presence of anionic chalcogen atoms in LaCuOCh is supported by the Ch binding energies, which undergo negative shifts proportional to the polarity of the Cu–Ch bonds.Figure optionsDownload as PowerPoint slideHighlights
► La 3d XPS confirms La–Ch interlayer interactions between [LaO] and [CuCh] layers.
► O 1s and Cu 2p XPS are insensitive to chalcogen substitution.
► Cu XANES spectra support the presence of Cu+ species.
► Negative shifts in Ch binding energies imply anionic chalcogen atoms.