Epitaxial zirconia and ceria thin films have been of interest recently as components of solid oxide fuel cells and other devices as well as means to study interfacial and strain effects on ion motion. These films are typically fabricated by one of a variety of physical vapor deposition methods. One difficulty in these studies is that the film composition is fixed by the composition of a ceramic or metal alloy target. Here, we demonstrate a means to produce epitaxial films with arbitrary dopant composition and Zr-Ce ratio. Reactive co-sputtering was performed using pure elemental targets of Zr, Ce, Y, and Gd onto (100) MgO substrates. The use of metal targets allowed for high purity and, by varying the relative sputtering powers and deposition time, the composition and thickness of single or multi-layer thin films was controlled. X-ray diffraction and transmission electron microscopy showed that yttria-stabilized zirconia (YSZ) films deposited on (100) MgO substrates at a substrate temperature of 400 degrees C were epitaxially grown along the (100) direction, while gadolinium doped ceria (GDC) films had no epitaxial relationship. Still, it was found that a YSZ film could be used as a buffer layer on the MgO substrates to enable epitaxial growth of the GDC film in the (100) orientation. (C) 2012 Elsevier B. V. All rights reserved.