ESCA studies of copper oxides and copper molybdates

Valence band, Cu 2p32, O 1s, Mo 3d, and Cu L3M45M45 photoelectron and X-ray-induced Auger spectra were recorded for metallic copper, Cu2O, CuO, Cu2Mo3O10, Cu6Mo4O15, CuMoO4, Cu3Mo2O9, and Cu3.85Mo3O12. Cu 2p32 binding energy is 0.9 eV lower for Cu+-containing molybdates than for Cu2O and 0.7 eV higher for Cu2+-containing molybdates with respect to that of CuO. Calculation of net chemical shift demonstrates the influence of Madelung potential on the binding energy of core electrons. On the basis of differences in binding energy it was possible to distinguish between various Cu-containing phases and to follow the surface redox processes of copper molybdates which, as it was seen, follow the same reactions as in the bulk processes. Auger spectra suggest the presence of a very thin layer of “surface phase” common for all five studied molybdates and independent of bulk structure and composition.