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

Abstract

The relationship between the polyatomic anion conduction and negative thermal expansion (NTE) in Sc2(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 Sc2(WO4)3. Using the same force-field a series of correlated WO 42- migrations are observed in extended isothermal-isobaric MD simulations. Tubandt-type electrolysis experiments confirmed that the mobile species in Sc2(WO4)3 is anionic. Scandium tungstate is thus the prototype of novel class of ionic conductors, a WO 42- anion conductors. The relationship of the ion transport in this unique ion conductors with polyatomic mobile charge carriers to the NTE is discussed. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.