Optical, x-ray, and band-structure studies of iodine at pressures of several megabars

Optical-reflectivity and x-ray-diffraction techniques have been used to determine the electronic properties and structure of iodine to 181 and 276 GPa, respectively, in the diamond-anvil cell. X-ray measurements were performed by energy dispersive diffraction with synchrotron radiation. Monatomic metallic iodine transforms to an fcc structure at 53 GPa that remains stable to the maximum pressure. At 276 GPa, the volume compression V/${\mathit{V}}_0$ is 0.324. Reflectivity data are consistent with a strong metallic character in iodine from 19 to 181 GPa. The linear muffin-tin orbital method has been used to calculate the equation of state to 500 GPa and to model the reflectivity of iodine at high pressures.