An Influence of the Pressure on Metastability of the HCP Phase of Solid Nitrogen

Abstract

A quenched disordered hep phase of solid nitrogen has been studied as a function of pressure (up to 20 kbar), in the temperature region where a dynamical crossover is observed between nearly free rotations and activated tumbling motion. At low pressure the crystal structure below the crossover temperature remains hep with the molecular orientations frustrated due to the incompatibility the strong quadrupolar interactions with a hexagonal lattice. At higher pressure (p ≥ 10 kbar) this frustrated structure is unstable and transforms into an orthorhombic structure. We conclude that pressure suppresses the frustrated state observed at zero pressure. This glassy system, with increasing pressure, relaxes into a metastable 2-sublattice structure with a herringbone (out of plane) order.