We have used oxygen-plasma-assisted molecular beam epitaxy to grow highly oriented Ce1-xSmxO2-delta films on single-crystal c-Al2O3. The samarium concentration x was varied in the range of 1-33 atom %. It was observed that dominant (111) orientation in Ce1-xSmxO2-delta films can be maintained up to about 10 atom % samarium concentration. Films higher than 10 atom % Sm concentration started to show polycrystalline features. The highest conductivity of 0.04 S cm(-1) at 600 degrees C was observed for films with similar to 5 atom % Sm concentration. A loss of orientation, triggering an enhanced grain-boundary scattering, appears to be responsible for the decrease in conductivity at higher dopant concentrations. (c) 2008 The Electrochemical Society.