Nonstoichiometric orthorhombic titanium oxide, TiO2−δ and its thermochromic properties

Redox relationship among anatase, rutile, and a new nonstoichiometric orthorhombic titanium oxide was elucidated. Single crystal of nonstoichiometric orthorhombic titanium oxide TiO1.94 was prepared by reducing a single crystal of rutile TiO2 at 950 °C in H2 for 1 h based on this relationship. The single crystallinity was demonstrated by both the Laue and the Debye–Scherrer methods. Temperature dependence of the conductivity and the reflectance spectrum was measured for the single crystal of TiO1.94, and it was found that the reflectivity in near-infrared region over 1700 nm gradually increased with increasing temperature. “Smart windows” using this titanium oxide was proposed.