Magnéli Ti4O7 thin film produced by stepwise oxidation of titanium metal foil

A 3-μm-thick film of Magnéli Ti4O7 was successfully fabricated on the surface of Ti metal foil by a stepwise oxidation process involving annealing at 973 K in air followed by heating to 1173 K under a low oxygen partial pressure. Transmission electron microscopy and high-angle annular dark-field scanning transmission electron microscopy showed that the Magnéli Ti4O7 phase consisted of a period of four layers of equiaxial grains several hundreds of nanometers in size. The black Magnéli Ti4O7 thin film formed by our process absorbed light in the visible and near-infrared regions.