Effect of combined Pd and Cu doping on microstructure, electrical and gas sensor properties of nanocrystalline tin dioxide

The effect of combined Pd and Cu doping on microstructure, electrical and gas sensor properties of nanocrystalline tin dioxide was studied. SnO2, SnO2(PdO), SnO2(CuO), and SnO2(PdO+CuO) films thickness of 0.8–1 μm with doping metal content 0.5–1.6 at.% were synthesized by aerosol pyrolysis. An average SnO2 grain size decreased with the addition of both Pd and Cu. The resistance measurements at 77–373 K showed that all types of doping induce resistivity increase accompanied by the appearance of conductivity activation process. Conductivity transients in the presence of CO were studied at 323–523 K. For the samples doped with Pd the sensor response to CO was found to be comparable with the resistivity increment induced by Pd incorporation into SnO2 matrix. To reveal the effect of CO on the conductivity the low temperature resistance was measured for the films in non-equilibrium state reached by cooling down the film exposed to CO at T=523 K. Experimental data proved that CO adsorption may be regarded as a factor neutralizing the Pd doping action on the films conductivity. The catalytic effect of Pd clusters was found in the interaction of SnO2(PdO+CuO) films with CO.