Limitations on the use of perovskite-structure oxides in gas sensing as a result of the concurrent operation of separate mechanisms

This paper addresses the consequences of operating a semiconducting oxide gas sensor with appreciable oxygen ion mobility within a temperature range where equilibration of the bulk oxygen content and surface reactions with reducing gases can proceed simultaneously. The investigations focus on the behaviour of an example of a perovskite material (LaFe0.95W0.05O3) stemming from standard perovskites, but having all alkaline ions substituted by rare earth, on its resistance and stability against sulfur-containing gases (H2S) and on its sensitivity towards some important reducing gases (carbon monoxide, ethanol, methane, propane). The experimental results provide responses to these latter four gases which are distorted by the superimposition of responses involving bulk oxygen equilibration upon the surface reactions with reducing gases. It is concluded that, although perovskite-structure oxides remain useful for oxygen monitoring at high temperature, their deployment for sensing reducing gases is problematical.