Structural and gas-sensing properties of WO3 nanocrystalline powders obtained by a sol-gel method from tungstic acid

WO₃ 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 WO₃ nanopowders obtained by the most common process of pyrolysis of ammonium paratungstate, usually used in gas sensors applications. Sol-gel WO₃ showed a high sensor response to NO₂ and low response to CO and CH₄. The response of these sensor devices was compared with that of WO₃ obtained from pyrolysis, showing the latter a worse sensor response to NO₂. Influence of operating temperature, humidity, and film thickness on NO₂ detection was studied in order to improve the sensing conditions to this gas.