The effect of Al addition on the gas sensing properties of Fe2O3-based sensors

Gas sensors based on alpha -Fe2O3(Al) have been studied experimentally and theoretically. Those with 9 mol% Al-added, sintered at 850 degreesC, exhibi t good gas sensing responses to CO and CH4. Well formed polycrystalline par ticles, essential to good gas sensing properties, are observed. XRD data sh ow that the Al is dissolved into the material. The improvement in the gas s ensing performance is attributed to the increase of the specific surface ar ea caused by this aluminum addition. Variation of surface energy due to the Al-doped iron(III) oxide is modeled with two- and three-dimensional period ic structures. The results show that stronger relaxation leads to a stabili zation of the surface in the case of Al addition compared to that without A l addition. Without relaxation, the non A-added surface has a much lower su rface energy than the Al-added surface. Although the energy difference betw een the relaxed surfaces is small, it indicates that the growth of Al-added iron oxide is less exothermic than that of pure iron oxide, which would ex plain the smaller particle size and hence the increased surface area observ ed after Al addition. (C) 2001 Elsevier Science B.V. All rights reserved.