Effects of microstructure of sintered tin oxide on gas-sensing sensitivity

Abstract

Tin oxide (SnO[superscript2]) gas sensor is a widely used material for gas sensor applications, its response being a change in conductance on exposure to oxidising or reducing gas. SnO[superscript2] based sensors are of particular interest due to their high sensitivity at relative low operating temperature. In this study, influences of the microstructure of sintered tin oxide on gas sensitivity and the influences of dopant concentration on the electronic structure and sensitivity to iso-butane of sintered SnO[superscript2] gas sensors are investigated. Sb-doped SnO[superscript2] gas sensors were prepared by a conventional mixed oxide method. SnO[superscript2] was doped with various concentration of Sb[superscript2]O[superscript3] (0.3-1.0wt%) and sintered in air or in N[superscript2] atmosphere. Structural and morphological changes of the samples were characterized by X-ray diffraction study (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). XRD study reveals that sintered Sb-SnO[superscript2] contains a cassiterite phase. SEM and TEM investigations of the samples sintered in air and N[superscript2] atmosphere show porous polycrystalline structure with grain size ranging from 50-300 nm. X-ray photoelectron spectroscope (XPS) analysis was carried out in order to investigate the oxidation states of Sn and Sb in the system and the Fermi level of Sb-doped SnO[superscript2]. Ultraviolet photoelectron spectroscope (UPS) study was used to investigate the valence state of Sb-SnO[superscript2]. From the XPS analysis, the splitting of Sn 3d peak cannot be observed and thus suggesting that the oxidation state of Sb-doped SnO[superscript2] is 4+ and/or 2+. Gas sensitivity are measured at temperature range of 300-400 degree celsius as iso-butane vapor is introduced into flowing dry air and correlated with the response time of gas-sensor. It was found that the gas sensitivity increases with the operating temperature and SnO[superscript2] doped with 0.8wt%Sb[superscript2]O[superscript3] sintered in air exhibits the highest sensitivity to iso-butane.