Intrinsic polyatomic defects in Sc2(WO4)3

The intrinsic formation of polyatomic defects in Sc-2(WO4)(3)-type structures is studied by Mott Littleton calculations and Molecular Dynamics simulations. Defects involving the WO42- tetrahedron are found to be energetically favorable when compared to isolated W and O defects. WO42- Frenkel and (2Sc(3+), 3WO(4)(2-)) Schottky defects exhibit formation energies of 1.23 eV and 1.97 eV, respectively and therefore may occur as intrinsic defects in Sc-2(WO4)(3) at elevated temperatures. WO42- vacancy and interstitial migration processes have been simulated by classical Molecular Dynamics simulations. The interstitial defect exhibits a nearly 10 times higher mobility (with a migration energy of 0.68 eV). than the vacancy mechanism (with a slightly higher migration energy of 0.74 eV) and thus should dominate the overall ionic conduction. Still both models reproduce the experimental activation energy (0.67 eV) nearly within experimental uncertainty. (C) 2010 Elsevier B.V. All rights reserved.