The crystal structure and oriented transformation of black phosphorus under high pressure

Single crystal X-ray analysis of black phosphorus, a narrow gap semiconductor with puckered layer structure, was performed under high pressure up to 4.7 GPa Pressure dependences of the lattice parameters show anisotropy, as reported in the literature. The length of the b axis and unit cell volume decrease Linearly with increasing pressure but show a bend at around 1.7 GPa, at which the vanishing of the energy gap was observed previously. Lengths of two different covalent bonds decrease with pressure and become equal around the above-described pressure. Transition pressure from the orthorhombic to the rhombohedral phase is 4.6 GPa. The crystal orientation between them at transition proposed by Kikegawa and Iwasaki was confirmed by the use of a single crystal.