Topotactic reduction yielding black titanium oxide nanostructures as metallic electronic conductors

Detailed analyses of reduced, single crystal, rutile-type TiO(2) via high-resolution transmission electron microscopy (TEM) are reported which reveal that the reduction proceeds topotactically via interstitial diffusion of Ti ions at low temperature, around 350 °C. This important finding encouraged the production of various nanostructured reduced titanium oxides from TiO(2) precursors with morphology retention, and in the process, the synthesis of black titanium oxide nanorods using TiO(2) nanorods was demonstrated. Interestingly, as opposed to the semiconductive behavior of Ti(2)O(3) synthesized at high temperature, topotactically synthesized Ti(2)O(3) exhibits metallic electrical resistance, and the value at room temperature is quite low (<6 μΩ m, comparable to graphite). These unique properties are probably due to the lattice strains generally observed for topotactically synthesized Ti(2)O(3). This work shows that topotactically reduced titanium oxides can have fascinating properties as well as nanostructures.