On the role of catalytic additives in gas-sensitivity of SnO2-Mo based thin film sensors

The experimental results show, that the doping of the SnO2 thin films with molybdenum ions increases the sensor response to alcohols and downshifts the sensor operating temperature. The effect is caused by the formation of substitutional solid solution of molybdenum ions in the SnO2 crystal lattice with stabilized interstitial Mo(V) ions. The formation of Mo(V) ions proceeds by the capturing the conductivity electrons localized in the oxygen vacancies by nearest neighbor Mo(VI) ions and their shift from the regular positions into interstitials of the rutile-type SnO2 lattice, causing the decrease of the electric conductance. The enhancement of SnO2 sensitivity to alcohols in the presence of homogeneously distributed molybdenum additive is closely connected with the high catalytic activity of molybdenum ions in the reactions of oxidizing dehydration of alcohols. The reaction proceeds by the radical mechanism with the elimination of hydrogen form CH2-group in the alcohol molecule. Hydrogen generated by the reaction reduces the oxide surface and thus increases the sensor conductivity. (C) 2001 Elsevier Science B.V. All rights reserved.