Bonding and chemical shifts in aluminosilicate glasses: importance of Madelung effects

A detailed study of the XPS binding energy shifts of Si 2p, O 1s and Zr 3d in a series of aluminosilicate glasses (a three oxide glass: SiO2-Al2O3-CaO, three four-oxide glasses: SiO2-Al2O3-CaO-TiO2, ZrO2 or CeO2, along with a six-oxide glass SiO2-Al2O3-CaO-TiO2-ZrO2-CeO2) is presented. Their composition is such that these glasses have the same mean electronegativity, so that no changes in the atomic charges is expected. The binding energy shifts are interpreted in terms of initial and final state effects, and the balance of charge transfer contribution and electrostatic effects is discussed. Referred to the ternary glass, the binding energy shifts of the Si 2p, O 1s and Zr 3d lines in the complex glasses are due to an initial state effect, as the extraatomic relaxation is similar along the glass series. These shifts originate from electrostatic Madelung effects, likely coming from a structural change induced by the presence of the other oxides TiO2, ZrO2 and CeO2. These structural effects make it impossible to deduce information on the atomic charges directly from the binding energy shifts, even in a qualitative way