Defect chemistry of Ti and Fe impurities and aggregates in Al2O3
Bristow, Jessica K.
Parker, Stephen C.
Royal Society of Chemistry (RSC)
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.
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
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