Soft X-ray spectroscopy of ferrous silicates |
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Authors: | Charles G. Dodd Paul H. Ribbe |
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Affiliation: | 1. Department of Geological Sciences, Virginia Polytechnic Institute and State University, 24061, Blacksburg, VA, USA
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Abstract: | Energy gaps and electrical conductivities in the ferrous silicates, Fe2SiO4 and FeSiO3, depend primarily on Fe-O bonding and may be studied by ultraviolet and soft X-ray spectroscopy. We have measured FeLII–III X-ray band spectra under conditions of “minimal” (I4, at 4.0 keV) and “high” (I10, at 10.0 keV) self absorption to determine 3d orbital energy levels, to delineate d states in the valence band, and to construct band gap models. Absorption spectra, I4/I10, were computed to determine vacant orbital levels in the gap. A difference function (I4–I10) has been proposed to identify X-radiation at photon energies above the measured LIII absorption edge, including high-energy, double-vacancy satellites and radiative transitions involving the anti-parallel (spin-down) d 6 electron in the ground state. The proposed band gap model for Fe2SiO4 is consistent with that of Nitsan and Shankland (1976), including an intrinsic transition of 6.5 eV and an energy gap of 7.8 eV. The 3d orbital energy level electronic structures are in general agreement with levels computed by Tossell et al. (1974) for [FeO6]10? in FeO using an SCF Xα cluster MO method. A high-energy, double-vacancy satellite was found at ~710.7 eV, and is presumed to originate from an LIIIMII,III initial state. The intensity of these satellites for the ferrous silicates and other iron compounds, and corresponding Fe LII/LIII intensity ratios are correlated with differences in band gap magnitudes and gap structure. Fe LII/LIII intensity ratios are not well correlated with iron oxidation state. |
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