Defect chemistry of Ti and Fe impurities and aggregates in Al 2O3

Jessica K. Bristow, Davide Tiana, Stephen C. Parker, Aron Walsh

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32 Scopus citations


We report a theoretical evaluation of the properties of iron and titanium impurities in sapphire (corundum structured α-Al2O 3). 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/Ti III → 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 Ti IV/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-(Ti IV/FeII), with the energy of electron transfer remaining unchanged. This journal is

Original languageEnglish
Pages (from-to)6198-6208
Number of pages11
JournalJournal of Materials Chemistry A
Issue number17
StatePublished - 7 May 2014


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