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 degreesC in H-2 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. (C) 2004 Elsevier Ltd. All rights reserved.