Photocurrent Spectroscopy in Corrosion and Passivity Studies. A Critical Assessment

Semi-empirical correlation between the band gap, Eg, of oxides and the difference of electronegativity of the oxide constituents is described trying to highlight its limits and potentialities. The extension of this correlation to mixed oxides and the consequent possibility to use it for relating the oxide composition to the band gap value is critically reviewed comparing the predicted Eg with the experimental values. Suggestions on how to account for polymorphs with different band gaps, and on how to explain Eg of mixed oxides with partners metals with a largely different electronegativity are discussed on the basis of experimental results reported in the literature.