The scandium tungstate [Sc2(WO4)3] material was investigated by using a combination of atomistic simulation and experimental techniques to probe the defect, dopant and ion conduction properties. The simulations reproduce the complex crystal structure with the calculated unit cell parameters within 0.8% of experimental data from diffraction studies. Frenkel and Schottky defect energies were calculated, suggesting that such intrinsic defects were not significant within the structure. Vacancy migration (O2− or Sc3+) was calculated to be unfavourable. Modelling the pathways of interstitial O2− and Sc3+ migration suggested that either mechanism was possible, although the process to create these defects was still not clear. Isovalent doping onto the Sc3+ site was shown to be energetically favourable for a range of ions (e.g., Ga3+, In3+, Yb3+). In terms of experimental doping studies, a range of strategies were tried in order to introduce either vacancies or interstitial ions. These attempts were unsuccessful, showing that aliovalent doping on either cation site was extremely difficult, and so deviations from the ideal stoichiometry appear unfavourable. Isovalent doping was favourable for a range of ions (e.g., Ga3+, Al3+, In3+) which support the modelling results. Impedance data suggested that the main conduction mechanism was ionic rather than electronic; in agreement with previous studies.

Simulation and Conductivity Studies of Defects and Ion Transport in Sc2(WO4)3. D.J.Driscoll, M.S.Islam, P.R.Slater: Solid State Ionics, 2005, 176[5-6], 539-46