Computer Modelling of Radiation Damage in Cation Sublattice of Corundum

Abstract

Results of quantum chemical computer simulations of close Frenkel defects in corundum crystals are presented and discussed. The conclusion is drawn that the energy barrier for a back recombination up to fourth nearest neighbours is less than 0.3 eV, i.e. such pairs should be unstable at temperatures above 40 K.

Single molecule power-law behavior on a crystalline surface

“…Extensive theoretical work in sapphire has shown that small polaron formation at vacancies, color centers, and interstitial sites is likely and that these states are stable, exist in multiple charge states, form preferentially Schottky defects, and are found at well-defined energies from 0.3 eV above the valence band maximum ͑VBM͒ to just below the conduction band minimum ͑CBM͒. [46][47][48][49] In particular, interstitial aluminum Al i 0 sites are predicted to lie with respect to the VBM at 4.8 eV ͑Ն3.7 eV with respect to the CBM; doubly occupied͒ or at 5.7 eV ͑Ն2.8 eV with respect to the CBM; singly occupied͒, 48 similar to F, doubly occupied F − and F 2 centers. 46,47 These states are available at room temperature as acceptor states for charge transfer from the molecular excited state with rates in excess of the observed on rates, therefore not contributing to the observed P͑ on ͒.…”

Low temperature X-ray luminescence of KNbO3 crystals

“…Furthermore such e ects should be much more pronounced in materials where vacancy and (or) interstitial defects have low activation energies for di usion. For instance, even in MgO, where intrinsic di usion of both F centres, oxygen vacancies begins above 1000 C, with the corresponding migration energies of 2.5±3.3 eV [28], and oxygen interstitials start to anneal out at 350 C (the corresponding migration energy of 1.6 eV) [29], 50% F centre ionization-induced annealing under sub-threshold electron irradiation was observed [27]. In KNbO 3 the e ects of ionizationinduced and thermally assisted annealing of close Frenkel defects should be much more e ective, due to very low oxygen vacancy migration energy of 0.7 eV [30], with appropriate migration temperature very close to RT.…”

Origin of n- and p-type conductivity in undoped α-PbO: role of defects

“…Analysis of the literature on defect formation in semiconductors [15] and particularly in simple oxides [16], has revealed that additionally to the vacancy defects investigated in our previous study [5], interstitials have to be considered. For crystalline materials, interstitial defects induce a large lattice distortion into their immediate neighbourhood that results in their high formation energy [15].…”