Mechanism of sensing NO in argon by nanocrystalline SnO2:: electron paramagnetic resonance, Mossbauer and electrical study

The mechanism of NO interaction with nanocrystalline (6-10 nm particle size) SnO2 powdered samples, obtained by sol-gel synthesis, was studied by electron paramagnetic resonance and Mossbauer spectroscopy. Resistance measurements on nanostructured (3 nm particle size) SnO2 thin films (80-160 nm), still obtained by sol-gel route, were coupled to spectral results. Spectroscopic investigations demonstrated that the NO interaction involves electron injection to the oxide, formation of oxygen vacancies, and chemisorption of NO2- and NO3- anions. The amount of oxygen vacancies depends on the annealing atmosphere of SnO2-. When it was previously annealed under inert (Ar) atmosphere, the NO interaction causes a great amount of oxygen defects as the lack of chemisorbed oxygen species forces NO to interact with lattice oxide anions; instead when annealed in air, NO also reacts with chemisorbed oxygen species giving NO2- and NO3- anions. Accordingly, the electrical response is higher in the case of predominant NO interaction with lattice oxide anions, because a great amount of NO electrons are transferred to SnO2. (C) 2003 Elsevier B.V. All rights reserved.