Scandia-stabilized zirconia films were epitaxially grown on sapphire (0001) substrates by oxygen-plasma-assisted molecular beam epitaxy. The cubic phase was found to exist over a wider dopant concentration range than previously observed (4.6-17.6 mol.% Sc2O3). The monoclinic phase was observed for dopant concentrations of 1.5 mol.% and 22.5 mol.%. An increase in the fraction of the monoclinic phase relative to the cubic phase decreased the ionic conductivity. The highest conductivity in the temperature range of 460-900 degrees C was observed for 9.9 mol.% Sc2O3. Atomistic computer simulations show that the observed composition dependence can be related to changes in migration barriers for O-2 ion transport with Sc3+ substitution of Zr4+ ions. (C) 2010 Elsevier B.V. All rights reserved.