Corundum Structure Oxides Studied by XPS

The electronic structure behaviour of Me 2 O 3 oxides (Me = Ti, V, Cr) has been determined from XPS valence band and core level measurements. From Ti to Cr sesquioxide the relative intensity of the 3 d band increases systematically which can be explained by the (atomic) photoelectric cross section and the number of 3 d electrons. Simultaneously the 3 d -2 p band separation decreases indicating a more stronger band overlap equivalent an enhanced covalent bonding component. The different electrical properties among the corundum structure oxides are determined by the trigonal field splitted a 1 g and e g orbitals, their occupation and relative energy position at the Fermi level. The observations confirm the change from itinerant to more localized behaviour of d electrons caused by crystal structure parameter change ( c/a ratio).