Pressure-induced phase transition, metallization, and superconductivity in boron triiodide

Pressure evolution of structural and electrical properties of boron triiodide, a highly anisotropic molecular crystal consisting of stacked layers of planar BI3 molecules, has been studied by x-ray diffraction and resistivity measurements. A new phase transition was observed to occur at 6.2 GPa from the molecular phase with hexagonal structure to a monatomic phase with the face-centered-cubic lattice of iodine atoms. This first-order phase transition is characterized by the discontinuous crush of stacking of molecular layers. The monatomic phase becomes metallic at similar to 23 GPa and exhibits superconductivity above similar to 27 GPa. The process of molecular dissociation and electrical properties of BI3 are discussed in comparison with those of iodine and other simple molecular iodides.