Tungsten oxide W18O49 nanowires with diameters of 10–20nm were synthesized with high yield by thermal evaporation in a tube furnace. By heating tungsten trioxide powder at 900°C in vacuum (5×10−3torr), W18O49 nanowires with diameters of 10–20nm and lengths up to micrometers were produced with high yield on the Au-coated Si substrates located in the low temperature zone (550–600°C) of the furnace. The morphology, composition, and crystal structure of the nanowires were characterized by various methods. The conditions and the mechanism of W18O49 nanowire growth are discussed.

Tungsten oxide is one of the most important transition metal oxide materials, which possesses some unique properties such as electrochromic, optochromic, and gaschromic properties. In this paper, we report a simple method for synthesizing high quantity tungsten oxide nanoribbons by oxidizing a tungsten plate under moist conditions. Using potassium iodide as the catalyst, tungsten oxide nanoribbons with a thickness of 40-100 nm, width up to 1 µm and length up to hundreds of micrometres are obtained on a large scale. The morphology, composition and crystal structure of the nanoribbons are characterized by various methods, such as scanning electron microscopy, transmission electron microscopy and x-ray diffraction. The nanoribbons comprise mainly monoclinic tungsten trioxide (WO 3 ) growing along the [001] direction and the orthorhombic WO 3 (H 2 O) 0.33 . The measured lattice parameters are β = 89.93 • , a = 0.7274 nm, b = 0.7501 nm, c = 0.3824 nm for WO 3 and a = 0.7359 nm, b = 1.251 nm, c = 0.7704 nm for WO 3 (H 2 O) 0.33 , respectively.

We report the synthesis of tungsten oxide W18O49 nanowires by thermal evaporation at low temperature without using catalysts. By placing tungsten powder in the high temperature zone at 650 °C and tungsten substrate in the low temperature zone at 400 °C of a tube furnace, W18O49 nanowires with diameters of 10–50 nm are produced with high yield. The nanowires extend to 500–1500 nm length, and the cross-sectional shapes are circular or polygonal. The roles of the source material, the pre-oxide layer on the substrate and the temperature of the reactor are also investigated. It is shown that the presence of oxygen on the W surface is essential for tungsten oxide nanowire growth.

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