Room-temperature response of platinised tin dioxide gas-sensitive resistors

Abstract

Pt-decorated SnO₂ gas-sensitive resistors have been produced which exhibit a practically useful room-temperature response to CO, the magnitude of which is dependent on the Pt loading and the decomposition temperature following the Pt impregnation step. The effect of increasing the decomposition temperature in the range 300–800 °C was twofold: the platinum particle size increased from ca. 1 to 10 nm and the Pt speciation changed from Pt° and Pt(OH)₂ species to essentially PtO and PtO₂. The behaviour of the materials was consistent with a model in which CO reacted with chemisorbed oxygen at the Pt/oxide interface and modulated the Schottky barrier height at intergrain contacts. The gas response exhibited a power-law dependence on CO concentration (Δσ/σ₀=k[CO]^β), with values for the response exponent, β, between 0.2 and 1. The conductance in the pellets was interpreted in terms of a three-phase (gas–SnO₂–Pt–SnO₂) percolation model.