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

Abstract

Gas sensors based on α-Fe₂O₃(Al) have been studied experimentally and theoretically. Those with 9 mol% Al-added, sintered at 850°C, exhibit good gas sensing responses to CO and CH₄. Well formed polycrystalline particles, essential to good gas sensing properties, are observed. XRD data show that the Al is dissolved into the material. The improvement in the gas sensing performance is attributed to the increase of the specific surface area caused by this aluminum addition. Variation of surface energy due to the Al-doped iron(III) oxide is modeled with two- and three-dimensional periodic structures. The results show that stronger relaxation leads to a stabilization of the surface in the case of Al addition compared to that without Al addition. Without relaxation, the non Al-added surface has a much lower surface energy than the Al-added surface. Although the energy difference between 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 explain the smaller particle size and hence the increased surface area observed after Al addition.