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

The mechanism of NO interaction with nanocrystalline (6-10nm particle size) SnO₂ powdered samples, obtained by sol-gel synthesis, was studied by electron paramagnetic resonance and Mössbauer spectroscopy. Resistance measurements on nanostructured (3nm particle size) SnO₂ thin films (80-160nm), 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. © 2003 Elsevier B.V. All rights reserved.