Novel polyanion conduction in Sc2(WO4)3 type negative thermal expansion oxides

The relationship between the polyatomic anion conduction and negative thermal expansion (NTE) in Sc-2(WO4)(3) type structure has been investigated by a combination of computational, electrochemical and X-ray diffraction approaches. The motion of the effective charge carriers in solid-state ionics can be visualised by molecular dynamics (MD) simulations if proper initial structure and force-field are known. By successfully reproducing the NTE for a large temperature range, we have designed and verified a valid force-field to predict the mobile species in Sc-2(WO4)(3). Using the same force-field a series of correlated WO42- migrations are observed in extended isothermal-isobaric MD simulations. Tubandt-type electrolysis experiments confirmed that the mobile species in Sc-2(WO4)(3) is anionic. Scandium tungstate is thus the prototype of novel class of ionic conductors, a WO42- anion conductors. The relationship of the ion transport in this unique ion conductors with polyatomic mobile charge carriers to the NTE is discussed. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim