Mechanism Of Pressure Induced Amorphization Of Sni4: A Combined X-Ray Diffraction-X-Ray Absorption Spectroscopy Study

We have studied the amorphization process of SnI4 up to 26.8 GPa with unprecedented experimental details by combining Sn and I K-edge x-ray absorption spectroscopy and powder x-ray diffraction. Standard and reverse Monte Carlo extended x-ray absorption fine structure (EXAFS) refinements confirm that the penta atomic SnI4 structural unit tetrahedron is a fundamental structural unit that appears preserved through the crystalline phase-I to crystalline phase-II transition that has been previously reported between 7 GPa and 10 GPa. Up to now, unexploited iodine EXAFS reveals to be extremely informative and confirms the progressive formation of iodine-iodine short bonds close to 2.85 angstrom. A coordination number increase of Sn in the crystalline phase-II region appears to be excluded, while the deformation of the tetrahedral units proceeds through a flattening that keeps the average I-Sn-I angle close to 109.5 degrees. Moreover, we put in evidence the impact of pressure on the Sn near edge structure under competing geometrical and electronic effects.