Stability and Controlled Composition of Hexagonal WO 3
2008; American Chemical Society; Volume: 20; Issue: 12 Linguagem: Inglês
10.1021/cm800668x
ISSN1520-5002
AutoresImre Miklós Szilágyi, János Madarász, György Pokol, P. Király, Gábor Tárkányi, Sami Saukko, J. Mizsei, A.L. Tóth, András Szabó, Katalin Varga-Josepovits,
Tópico(s)Conducting polymers and applications
ResumoThis paper discusses the formation of nanosized hexagonal tungsten oxide (h-WO3) during the annealing of hexagonal ammonium tungsten bronze (HATB), (NH4)0.33−xWO3−y. This process was investigated by TG/DTA-MS, XRD, SEM, Raman, XPS, and 1H-MAS NMR analyses. Through adjusting the temperature and atmosphere of annealing HATB, the composition (W oxidation state, residual NH4+ and NH3 content) of h-WO3 could be controlled. The effect of composition on the conductivity and gas sensitivity of h-WO3 was studied. New structural information was obtained about both HATB and h-WO3. It was found that NH4+ and NH3 could be situated at three different positions in HATB. Residual NH4+ and NH3 in the hexagonal channels seemed to be vital for stabilizing h-WO3: when they were completely released, the hexagonal framework collapsed. We propose that the structure of h-WO3 cannot be maintained without some stabilizing ions or molecules in the hexagonal channels.
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