A Mössbauer study of the amorphous tin-oxide system

The structure of the Sn-O bonding and lattice dynamics of amorphous tin-oxide were studied by Mössbauer spectroscopy (MS), electro-micrography and electron diffraction. Samples were prepared by direct reaction of O₂ gas and Sn vapour condensed on a substrate cooled to 100 K. Studies were performed with various O₂/Sn concentration. It was found that despite the existence of the amorphous state determined by electron diffraction and electro-micrography, the MS results, namely the hyperfine interaction and temperature dependence of the recoil-free-fraction data, were the same as that obtained from polycrystalline materials. Only at extremely high concentration of O₂ (10^-3 torr) and tin deposition rate of 20 Å s^-1 a distinct change is observed in the isomer shift, quadrupole splitting and Debye temperature (⊖_D) of the tin-oxide composed of SnO and SnO₂ species. This high degree of amorphicity is preserved at least up to 450 K. It is unequivocally concluded that in the tin-oxide systems drastic decrease in ⊖_D is coupled to disorder of Sn-O bond, down to the atomic scale of nearest and next nearest neighbours. The MS in this respect is a unique tool for determining the amorphous state of oxide systems.