A transparent, high purity, amorphous titanium dioxide thin film composed of densely packed nanometersized grains has been successfully deposited on a glass substrate at room temperature from an aqueous peroxotitanate solution using a simple, inexpensive, reproducible, and environmentally friendly method. The as-deposited thin film was 117 nm thick and composed of closely packed particles of 10-15 nm in diameter, but they aggregated into large grains of 50-100 nm in diameter. The aqueous peroxotitanate solution was obtained by dissolving metatitanic acid (H 2 TiO 3 ) in a mixture of concentrated H 2 O 2 and NH 3 ?H 2 O. An anatase TiO 2 thin film was obtained by heating the as-deposited thin film at 500 uC for 1 h in air. A chemical composition of TiO 1.4 (O 2 ) 0.5 (OH) 0.2 ?1.34H 2 O is proposed for the as-deposited thin film, based on XPS, FT-IR and TG-DTA data. Band gap energies of 3.20 eV for indirect transition and 3.63 eV for direct transition were obtained for the anatase TiO 2 film.

Tungsten-doped vanadium dioxide (VO 2 ) nanopowders were synthesized by thermolysis of (NH 4 ) 5 [(VO) 6 -(CO 3 ) 4 (OH) 9 ]‚10H 2 O at low temperature with, to the best of our knowledge, active white powdery tungstic acid (WPTA) used as a substitutional dopant for the first time. The change in electrical resistance due to the semiconductor-metal transition was measured from -5 to 150 °C by the four-probe method. Differential scanning calorimetry and the resistance-temperature curve of the nanopowders indicated that the phase transition temperature of VO 2 powders was 67.15 °C, but for W-doped VO 2 , the temperature was reduced to 26.46 °C. The results indicated that WPTA was found to be exceptionally effective as a dopant for reducing the transition temperature.

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