Influence of the catalytic introduction procedure on the nano-SnO2 gas sensor performances -: Where and how stay the catalytic atoms?

The role and activity of catalytic additives on solid-state gas sensors are determined by the additive chemical state, aggregation form and interaction with the semiconductor oxide. All these parameters depend on the technological steps involved in the element introduction and the treatments applied to the sensor material. The aim of this work is to analyse the influence of the additive introduction procedure on the gas sensor performance. In order to achieve this objective, two sets of different palladium, platinum or gold modified tin oxide materials have been prepared. In a first set of samples, additives were introduced by impregnation of the previously thermally stabilised oxide. In the second set, catalyst addition was carried out before any thermal treatment was applied. The study of the catalytically modified materials. calcined at different treatment temperatures between 250 and 1000 degreesC, has been performed by means of HRTEM, XRD, XPS, and Raman spectroscopy. The influence of both processes on additive surface concentration, chemical state, nanoparticle growth and resistivity values are presented and discussed. Moreover, electrical characterisation of the sensors prepared from these materials has been carried out. (C) 2001 Elsevier Science B.V. All rights reserved.