Sol–gel preparation and characterization of black titanium oxides Ti₂O₃ and Ti₃O₅

Sub-micron black titanium oxides powders Ti₂O₃ and Ti₃O₅ were synthesized via a facile and economical sol–gel method in this paper. Relatively pure Ti₃O₅ and Ti₂O₃ can be obtained by annealing the as-prepared PEG600-based gel with a heating rate of 10 °C min⁻¹ and maintaining the temperature at 1,000 and 1,200 °C, respectively, under high pure (99.999 %) argon atmosphere for 4 h. The FESEM images reveal that the morphologies of the as-prepared Ti₃O₅ and Ti₂O₃ are sphere-like and plate-like mixed type structures. The particle size of Ti₃O₅ sample is in the range of 50–200 nm. However, the appearance of Ti₂O₃ is 200–500 nm irregular flake structures covered with 20–50 nm spherical particles. This PEG600-based sol–gel approach has a low reaction temperature of 1,000 °C herein for the preparation of Ti₃O₅, which is ascribed to that, the molecular PEG-600 was distributed well in the homogeneous gel through secondary cross-linking of the organic molecules, and with the increasing of heating temperature, molecular PEG-600 was carbonized. These nanoscaled and homogeneous mixtures of carbon and TiO₂ made the carbon thermal reduction reaction occur subsequently at 1,000 °C. The Raman vibrational wavenumbers of as-prepared Ti₃O₅ and Ti₂O₃ are perfectly coincident with those of calculated results of pure Ti₃O₅ and Ti₂O₃. Besides, the Fourier transform infrared spectra of Ti₃O₅ and Ti₂O₃ were also investigated in this article. Finally, the powder electrical resistivity of Ti₃O₅ and Ti₂O₃ is 4.7 × 10⁻³ and 2.5 × 10⁻³ Ω m, respectively.