Effect of pressure on bonding in black phosphorus

Abstract

The bond lengths and bond angles of orthorhombic black phosphorus have been determined as a function of hydrostatic pressures to 26.6(5) kbar using time‐of‐flight neutron powder diffraction. We show that the markedly anisotropic compression reported previously results from a large pressure‐induced shortening of the van der Waals bonds separating layers of atoms combined with a shear motion within the layers. Covalently bonded chains of atoms along the a direction remain very rigid. The average effective linear compressibility for van der Waals bonds is 1.48(9) ×10⁻³ kbar⁻¹ while the average effective linear compressibility for covalent bonds is an order of magnitude smaller, 2.6(8) ×10⁻⁴ kbar⁻¹.