The influence of shallow core-level hybridization on the electronic structure of the post-transition metal oxides ZnO, CdO, In 2 O 3 , and SnO 2 has been investigated using high-resolution soft x-ray emission and absorption spectroscopies. Synchrotron radiation excited O K ␣ emission spectra provide a direct measure of the O 2p partial density of states and shallow core-level hybridization for this series of transparent conducting materials and reveal significant mixing of O 2p and shallow-core metal d states for ZnO, CdO, and In 2 O 3 . The experimental data are compared with local density approximation and tight-binding band structure calculations and with previous experimental determinations of direct and indirect band gaps. Rocksalt CdO, bixbyite In 2 O 3 , and rutile SnO 2 all adopt structures with metal cations in sites with locally centrosymmetric coordination. This prevents hybridization of O 2p states with metal 4d states at the zone center, but mixing away from ⌫ leads to indirect band gaps for CdO and In 2 O 3 . A revised value for the lowest indirect band gap in CdO is proposed and the overall trends in the band gap are discussed in terms of the separation between O 2p and metal 4d states. The experimental investigation has been extended to study the effects of Sn doping in In 2 O 3 .

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The orbital character, orientation, and magnetic polarization of the O-2p unoccupied states near the Fermi level (E F ) in CrO 2 was determined using polarization-dependent x-ray absorption spectroscopy and x-ray magnetic circular dichroism from high-quality, single-crystal films. A sharp peak observed just above E F is excited only by the electric-field vector (E) normal to the tetragonal c axis, characteristic of a narrow band (Ϸ0.7 eV bandwidth͒ constituted from O-2p orbitals perpendicular to c (O-2p y ) hybridized with Cr 3d xzϪyz t 2g states. By comparison with band-structure and configuration-interaction cluster calculations our results support a model of CrO 2 as a half-metallic ferromagnet with large exchange-splitting energy (⌬ exchϪsplit Ϸ3.0 eV͒ and substantial correlation effects.

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