Effect of composition on sensing properties of SnO2Â +Â In2O3 mixed nanostructured films

The conductometric response of SnO2 + In2O3 nanocomposite films to hydrogen and carbon monoxide in air are investigated experimentally for varying oxide compositions. The fundamental mechanism of sensory phenomena in such nanocomposite films is also discussed. The experimental results indicate that the response (θcom) of the sensor is determined by the current flow path in the film. For composites with In2O3 composition (XIn) less than 20 wt.%, current flows through the SnO2 crystals. Due to electron transfer from the In2O3 inclusions to the SnO2 matrix, an increase in XIn up to 20 wt.% leads to a significant increase in the conductivity of the composite sensor and θcom for both CO and H2. A further increase in XIn results in percolation transition for In2O3 nanocrystals, which form conducting clusters (threads) of In2O3, with electrical conductivity that is much higher than that of SnO2. The transition from conduction through the SnO2 crystals to conduction through the In2O3 crystals in the composite films occurs at XIn in the range about 20-50 wt.%. For XIn ≥ 50 wt.%, θcom is entirely determined by the sensory properties of the In2O3 conducting clusters, and electron transfer from In2O3 clusters to SnO2 results in a decrease of θcom.