EFFECT OF PRESSURE ON BONDING IN BLACK PHOSPHORUS

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. © 1979 American Institute of Physics.