High-pressure Raman study of the iodine-doped silicon clathrate I8Si44I2

Raman scattering measurements of an iodine-doped I8Si44I2 clathrate have been performed at pressures up to 28 GPa and 296 K. We found two Raman peaks at 75 and 101 cm-1 associated with the vibrations of guest I atoms inside the host Si cages, and observed some framework vibrations around 120–500 cm-1. These characteristic Raman bands and their pressure dependence are investigated in consideration of our recent Ba8Si46 studies. The lowest-frequency framework vibration at 133 cm-1 shows the softening with pressure, which seems to be the common feature of Si clathrates. A strong and broad Raman band centered at 461 cm-1 is identified to the highest-frequency framework vibration, which is likely intensified and broadened by the considerable framework distortion due to the replacement of framework Si with larger I atom. No obvious pressure-induced phase transition was found up to 28 GPa. The guest-host interactions are investigated by the present vibrational properties and are compared with those of previous neutron studies of I8Si44I2