Intrinsic polyatomic defects in Sc2(WO4)3

The intrinsic formation of polyatomic defects in Sc2(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 (2Sc3+, 3WO42−) Schottky defects exhibit formation energies of 1.23 eV and 1.97 eV, respectively and therefore may occur as intrinsic defects in Sc2(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.