Mechanism of defect formation and polyanion transport in solid scandium tungstate type oxides

Abstract

The unique diffusion mechanism in the novel polyatomic anion conductor scandium tungstate is studied by molecular dynamics simulations of systems with artificially induced WO4 2- defects and compared to our previous simulations of defect-free structure models. The diffusion activation energy obtained from structures with built-in defects is smaller than for the defect-free models and in the case of tungstate vacancies close to the experimental value, suggesting that extrinsic tungstate vacancies due to the volatility of WO3 are important for the experimental conductivity. The validity of the force field used for the molecular dynamics simulations is further verified by investigating the orthorhombic to monoclinic phase transition of Sc2(WO4)3 under compression. The lattice compressibility in both phases and the phase transition is qualitatively reproduced, though the simulated phase transition pressure occurred is about 0.55 GPa higher than the experimental one. © 2009 Springer-Verlag.