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Defect chemistry of Ti and Fe impurities and aggregates in Al2O3
Bristow, Jessica K.; Tiana, Davide; Parker, Stephen C.; Walsh, Aron
We report a theoretical evaluation of the properties of iron and titanium impurities in sapphire (corundum structured α-Al2O3). Calculations using analytical force fields have been performed on the defect structure with the metals present in isolated, co-doped and tri-cluster configurations. Crystal field parameters have been calculated with good agreement to available experimental data. When titanium and iron are present in neighbouring face and edge-sharing orientations, the overlap of the d-orbitals facilitates an intervalence charge transfer (FeIII/TiIII → FeII/TiIV) with an associated optical excitation energy of 1.85 eV and 1.76 eV in the respective configurations. Electronic structure calculations based on density functional theory confirm that FeIII/TiIII is the ground-state configuration for the nearest-neighbour pairs, in contrast to the often considered FeII/TiIV pair. Homonuclear intervalence charge transfer energies between both FeIII/FeII and TiIV/TiIII species have also been calculated, with the energy lying in the infra-red region. Investigation of multiple tri-clusters of iron and titanium identified one stable configuration, TiIII–(TiIV/FeII), with the energy of electron transfer remaining unchanged.
Keyword(s): Generalized gradient approximation; Transition-metal ions; Charge-transfer band; Sapphire thin-films; Doped sapphire; 1st-principles calculations; Electron localization; Polycrystalline AL2O3; Optical-spectra; Blue sapphire
Publication Date:
Type: Journal article
Peer-Reviewed: Yes
Language(s): English
Institution: University College Cork
Citation(s): Bristow, J. K., Tiana, D., Parker, S. C. and Walsh, A. (2014) 'Defect chemistry of Ti and Fe impurities and aggregates in Al2O3', Journal of Materials Chemistry A, 2(17), pp. 6198-6208. doi: 10.1039/c3ta15322c
Publisher(s): Royal Society of Chemistry (RSC)
File Format(s): application/pdf
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First Indexed: 2018-07-06 06:30:38 Last Updated: 2018-07-06 06:30:38