High-pressure isostructural transition in nitrogen

TL;DR

This study investigates high-pressure phase transitions in nitrogen, revealing an isostructural transition at 54 GPa that provides insights into nitrogen's dissociation behavior under extreme conditions.

Contribution

The paper reports the first observation of an isostructural transition in nitrogen using Raman and X-ray diffraction techniques, expanding understanding of nitrogen's high-pressure phases.

Findings

Isostructural transition observed at 54 GPa

Discontinuity in unit cell parameters at transition

Vibron broadening and turnover at transition pressure

Abstract

Understanding high-pressure transitions in prototypical linear diatomic molecules, such as hydrogen, nitrogen, and oxygen, is an important objective in high-pressure physics. Recent ultrahigh-pressure study on hydrogen revealed that there exists a molecular-symmetry-breaking isostructural electronic transition in hydrogen. The pressure-induced symmetry breaking could also lead to a series of solid molecular phases in nitrogen associated with the splitting of vibron, walking a path from fluid nitrogen to molecular solids and then to polymetric nitrogen phases. However, isostructural transition in nitrogen has not been reported so far, which may provide crucial information on the crystallographic nature of the pressure-induced dissociation transitions in nitrogen. Here we present a high-pressure Raman scattering and high-pressure angle dispersive X-ray diffraction study of the previously reported lambda-N2 and reveal an isostructural transition from the lambda-N2 to a new derivative phase, lambda-N2. Under compression, lambda-N2 remains in the monoclinic crystal lattice, accompanied by a monotonic increase in anisotropy. The pressure-dependent decrease of the unit cell parameters exhibits a discontinuity at the pressure of 54 GPa, accompany with sudden broadening and turnover of vibron.