Microstructure evolution of radio-frequency magnetron sputtered oxide thin films in the Cr–Zr–O system

• Synthesis of Cr–Zr–O thin films by reactive radio-frequency magnetron sputtering
• Thin films with various oxide structures were grown.
• Single-phase solid solution corundum (Cr,Zr)2O3 thin films at low Zr content
• Single-phase solid solution cubic (Zr,Cr)O2 thin films at medium Zr content
• Two-phase tetragonal and monoclinic composite thin films at high Zr content

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)2O3 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.