Pressure Dependence of the Lattice Vibration in the Orthorhombic and Rhombohedral Structures of Black Phosphorus

Abstract

The lattice vibration of black phosphorus was investigated under hydrostatic high pressure by polarized Raman scattering. On applying pressure the crystal structure changes to the rhombohedral A7-structure from the layered orthorhombic structure at 52 kbar. At atmospheric pressure four phonon modes are observed at 362 cm⁻¹ with A_g-symmetry, 467 cm⁻¹ A_g, 194 cm⁻¹ B_1g and 439 cm⁻¹ B_2g. The Grüneisen parameters are 0.74 for the 362 cm⁻¹ A_g-mode, 0.10 for the 467 cm⁻¹ A_g-mode and 0.22 for the 439 cm⁻¹ B_2g-mode. The energies of the latter two modes change little with pressure, since in these modes the atoms displace to deform the rigid zigzag chain along the a-axis. In the A7-structure the A_1g-mode was observed at 466 cm⁻¹ and the E_g-mode at 392 cm⁻¹. The comparison with the phonon modes in other group V materials was made.