X-Ray absorption study on the local structures of fine particles of α-Fe2O3–SnO2gas 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.