The pressure-induced metallic amorphous state of SnI₄. II. Lattice vibrations at the crystal-to-amorphous phase transition studied by Raman scattering

For pt.I see ibid., vol.18, p.789 (1985). The lattice vibrations in the molecular crystal SnI 4 have been investigated by high-pressure and high-temperature Raman spectroscopy. This material shows successive phase transitions at about 1.5, 10 and 20 GPa in a pressure-increasing process. Above 20 GPa an amorphous state is realised. On decreasing the pressure this amorphous state persists to about 2 GPa. Below this pressure the structure changes to another amorphous state and then a new crystal phase, at very close to atmospheric pressure. In the high-pressure amorphous state a strong A 1 -symmetric peak arising from the breathing mode of the SnI 4 tetrahedral molecules splits into a doublet. This is interpreted in terms of pressure-induced dimerisation. The spectra for the liquid are also measured, for comparison with those for the amorphous state.