Structural study on pressure-induced metallization of C6I6

High-pressure x-ray diffraction measurements of hexaiodobenzene (C6I6) have been carried out at room temperature using a helium pressure-transmitting medium. A 35 % compression in volume at 22 GPa maintained its monoclinic P2 (1)/c which was observed at atmospheric pressure, and involved remarkable d ecrease in b-axis length. The pressure changes of molecular form and orient ation had a direct influence on the variations in the intermolecular I-I di stances. It is speculated that the molecule takes the most favourable orien tation for reducing the volume, resulting in formation of a two-dimensional conductive network without molecular dissociation.