Mixed oxides as gas sensors

This paper reviews the current work carried out on mixed-oxide systems such as SnO2-WO3, TiO2-WO3 and SnO2-TiO2 with the ultimate aim of the applicati on in gas sensing devices. Special emphasis is put on a relatively new syst em, SnO2-TiO2. Materials have been prepared in a form of polycrystalline ce ramics and thin films by a variety of methods including impregnation, co-pr ecipitation, sol-gel and sputtering. The effect of the composition on the m icrostructure and surface morphology is discussed. The importance of non-de structive optical methods of measurements, especially those based on the us e of an integrating sphere, is pointed out. The sensor responses to hydroge n and methane are presented for SnO2-TiO2. (C) 2001 Elsevier Science B.V. A ll rights reserved.