X-Ray absorption study on the local structures of fine particles of α-Fe2O3–SnO2 gas sensors

Abstract

X-Ray absorption spectra (EXAFS) have been recorded of the local structure around iron and tin in fine powdery α-Fe₂O₃–SnO₂, prepared by thermal decomposition of coprecipitates from aqueous iron(III) sulfate and tin(IV) chloride solutions at pH 8. Tin atoms are substituted for iron atoms in the corundum structure of α-Fe₂O₃ below 15 mol% SnO₂ which is the limit of dissolution. Further addition of SnO₂ destabilises the system such that SnO₂enters the lattice as a substitutional defect. At > 50 mol%, SnO₂ forms a mixture of a rutile SnO₂ phase and an SnO₂ phase dissolved in α-Fe₂O₃. The Fe₂O₃(33 mol%)–SnO₂(67 mol%) structure consists of rutile SnO₂ and an irregular iron oxide phase. The high sensor sensitivity for CH₄ is intimately correlated with the amount of SnO₂ dissolved in α-Fe₂O₃.