Oxide thin films in the Cr-Zr-O system with various microstructures and properties were synthesized by reactive radio-frequency magnetron sputtering of a segmented chromium-zirconium target. Nanocrystalline Cr-Zr-O thin films with continuously changing compositions from chromium-rich to zirconium-rich were obtained in a single deposition process. The Cr-Zr-O thin films were characterized by electron probe microanalysis, X-ray diffraction and transmission electron microscopy. Up to a zirconium content of 12 at.% films with a metal/oxygen concentration ratio of 2/3 were deposited. These films revealed a single-phase solid solution (Cr,Zr)(2)O-3 corundum structure. An increasing zirconium (and decreasing chromium) concentration promoted the formation of ZrO2 structures accompanied by a change of the metal/oxygen concentration ratio towards 1/2. First, a cubic, then a tetragonal phase was formed, while at the highest zirconium content a monoclinic phase evolved in addition to the tetragonal phase. Microindentation analysis showed for the single-phase corundum films an increase in hardness of about 20% to 19 GPa with an increase of the zirconium content from 8 at.% to 12 at.%. Films with a ZrO2 structure exhibited indentation hardness values superior to those reported for bulk cubic and monoclinic ZrO2. (C) 2013 Elsevier B.V. All rights reserved.