ESCA studies of copper oxides and copper molybdates

Valence band, Cu 2p _{3}/{2}, O 1s, Mo 3d , and Cu L₃M₄₅M₄₅ photoelectron and X-ray-induced Auger spectra were recorded for metallic copper, Cu ₂O, CuO, Cu ₂Mo ₃O ₁₀, Cu ₆Mo ₄O ₁₅, CuMoO ₄, Cu ₃Mo ₂O ₉, and Cu _3.85Mo ₃O ₁₂. Cu 2p _{3}/{2} binding energy is 0.9 eV lower for Cu ⁺-containing molybdates than for Cu ₂O and 0.7 eV higher for Cu ²⁺-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.