EXAFS and XANES study of two novel Pd doped Sn/SnOx nanomaterials

Abstract

EXAFS and XANES at the Pd and Sn K-edges have been used to characterise a novel palladium doped Sn/SnOx nanocomposite that have found application in a new type of high performance solid-state gas sensor. The spherical nanoparticles (10 to 65 nm diameter) prepared either by co-decomposition of Sn and Pd organometallic precursors (doping in volume) or by decomposition of a palladium precursor on preformed Sn/SnOx coreshell nanoparticles (doping in surface) consist of a tin metallic core surrounded by some small platelets of a well-crystallised material embedded in an outer layer of amorphous tin oxide. In this layer tin atoms in an oxidation state close to +IV, are four-fold coordinated to oxygen with bond distances slightly larger than in bulk cassiterite SnO2. In both samples palladium was found to be always in a metallic state, only surrounded by Sn and Pd atoms located at unusually short distances. The two samples that differ mainly by their Pd coordination number present very different morphologies and electrical properties when fully oxidised. A possible location of the Pd atoms in these two materials is proposed.