The influence of nonstoichiometry on electrical transport and ethanol sensing characteristics for nanocrystalline LaFexO3 − δ sensors

Nonstoichiometric nanocrystalline LaFexO3 − δ(x = 0.7/0.8/0.9/1.0/1.1/1.2/1.3) powers were prepared by sol–gel method with citric acid. Temperature dependence of resistance for LaFexO3 − δ sensors fits best to Holsteins model of small polaron hopping conduction. The resistance is determined by the competition between electrical valence compensation and oxygen vacancy compensation. And at each fixed temperature, the resistance is decreased with the introduction of more Fe deficiency. XPS analysis on O1s and C1s spectra verifies the existence of La-carbonate on the surface. The variation of surface concentration of adsorbed oxygen and La-carbonate, atomic ratio of Fe4+/Fe3+ and Fe/La with x value are discussed in combination, which indicate that the release of electrons trapped by native active oxygen due to the decomposition of monodentate La-carbonate also makes contribution to the response of LaFexO3 − δ sensors to ethanol, in addition to the major contribution from adsorbed oxygen species. The best sensing performance of nanocrystalline LaFe0.8O3 − δ sensor is ascribed to its relatively large surface concentration of adsorbed oxygen species and monodantate La-carbonate.