Structure of pressure-induced amorphous form ofSnI4at high pressure

Abstract

The structure of pressure-induced amorphous form of ${\text{SnI}}_{4}$ has been studied by synchrotron x-ray diffraction measurements using diamond-anvil cell. The structure factor, the reduced radial distribution function, and the density were obtained between 25 and 55 GPa. Comparison of measured structure factor with that calculated for a randomly oriented dimerized molecules model shows no similarity between them. Experimentally obtained radial distribution function provides clear evidence for the absence of both distances between tin and iodine atoms and between iodine atoms within the ${\text{SnI}}_{4}$ tetrahedral molecule. Characteristic features of the structure factor for amorphous ${\text{SnI}}_{4}$ show a marked resemblance to those for elemental metallic glasses which are successfully reproduced by a model of dense random packing of equal-sized spheres. Indeed, various quantities such as positions of peaks in measured structure factors and in experimental radial distribution functions, the coordination number are in precise agreement with those derived from the dense random-packing model. We conclude that the structure of the high-pressure amorphous form of ${\text{SnI}}_{4}$ is the relatively rigid packing of tetrahedra composed of iodine and substitutional tin atoms.