WO/sub 3/ nanocrystalline powders were obtained from tungstic acid following a sol-gel process. Evolution of structural properties with annealing temperature was studied by X-ray diffraction and Raman spectroscopy. These structural properties were compared with those of WO/sub 3/ nanopowders obtained by the most common process of pyrolysis of ammonium paratungstate, usually used in gas sensors applications. Sol-gel WO/sub 3/ showed a high sensor response to NO/sub 2/ and low response to CO and CH/sub 4/. The response of these sensor devices was compared with that of WO/sub 3/ obtained from pyrolysis, showing the latter a worse sensor response to NO/sub 2/. Influence of operating temperature, humidity, and film thickness on NO/sub 2/ detection was studied in order to improve the sensing conditions to this gas.
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Jiménez et al. (2002) studied this question.
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