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Electronic state of oxygen in oxide minerals

¹ Crystallography and Mineralogy Centre, IICT, and CENIMAT, Mat. Sc. Dept., New University of Lisbon, P-2829-516 Caparica, Portugal
² Geophysics Centre, University of Évora, Apt. 94, P-7000 Évora, Portugal, e-mail: jmirao@uevora.pt

^* Corresponding author, e-mail: crysmin{at}clix.pt

The results are reported here of a XAS study of the O K-edge in oxide minerals, focused on triangular (C₂ site symmetry) and tetrahedral (T_d, C₂ and C₁) environments involving diverse coordinating cations within four crystal structure types: rutile-type (rutile, pyrolusite and cassiterite), fluorite-type (thorianite), spinel-type (spinel s.s.) and garnet-type (andradite). Full multiple-scattering calculations are compared to actual spectra with the aim of interpreting pre-edge peaks and post-edge features. Comments are presented on the role of combinations between O 2p and metal valence bands. It is concluded that the details and the energy of the O K-edge are influenced by the electronic state and coordination geometry of the surrounding cations in connection with the site symmetry constraints of the coordinated oxygen atoms within the host crystal structure.

Key-words: oxygen, XAS, multiple-scattering, minerals, bonding, K-edge..