Study of the behaviour of CeO₂ in SO₂-containing environment

The undoped n-type semiconductor CeO₂ is a less studied but in many respects promising potential new sensor material. As in our former experiments (using different reactive gases) CeO₂ proved to be a highly corrosion-resistant material, in this work detailed investigations have been carried out on its electrical and corrosion behaviour in a wide temperature range (300-800 °C) in oxygen- and SO₂-containing atmospheres. Our most important results can be summarized as: (a) the resistance of CeO₂ is practically uninfluenced either at 350 or 800 °C by SO₂ if oxygen is present; (b) around these two temperatures no corrosive effect of SO₂ can be observed either; (c) but at 550 °C in the presence of oxygen, the acceptor effect of SO₂ can be observed; (d) at 550 °C during long-term heat treatment (100 h) in an SO₂- and oxygen-containing atmosphere, the CeO₂ in a thin surface layer transforms into CeO and the same time a reversible incorporation of a few percent of S into this layer can be observed. In the present work the connection between the sensitivity maximum for SO₂ found at 550 °C in the presence of oxygen and a possible surface phase transformation is discussed.