SEMIEMPIRICAL CORRELATION BETWEEN OPTICAL BAND-GAP VALUES OF OXIDES AND THE DIFFERENCE OF ELECTRONEGATIVITY OF THE ELEMENTS - ITS IMPORTANCE FOR A QUANTITATIVE USE OF PHOTOCURRENT SPECTROSCOPY IN CORROSION STUDIES

A semiempirical correlation between the optical band gap of binary oxi des and the difference of electronegativity between the oxygen and met allic elements (Pauling's extraionic energy) is proposed. In the frame of the proposed correlation an estimate of the repulsive term in the total lattice energy of ionic oxides is obtained in very good agreemen t with the existing data. An extension of the correlation to the terna ry oxides and hydroxides is proposed by using the concept of average c ationic or anionic group electronegativity. The usefulness of the prop osed correlation for the in situ characterization of passive films on metals and alloys by photocurrent spectroscopy is illustrated by repor ting some preliminary experimental results on Sn and AlTi alloy.