Molecular nitrogen exhibits remarkable structural diversity near the polymeric transition, where multiple phases are metastable. Here, we report two new molecular phases. The first, tζ-N2, is a polytype of monoclinic C2/cζ-N2, characterized by a tripled c axis and 96 atoms per unit cell. The second, ξ-N2, is a previously unreported hexagonal phase (P6cc) containing 112 atoms per unit cell. Both phases were synthesized in a diamond anvil cell by laser heating ζ-N2 to 1800--2500~K at pressures of 78--98~GPa. Their crystal structures were determined using single-crystal X-ray diffraction, corroborated by Raman spectroscopy, and supported by first-principles calculations. The tζ-N2 phase likely corresponds to the previously reported κ-N2 phase.
@article{arxiv.2604.16641,
title = {Two New Molecular Nitrogen Phases near Megabar Pressures},
author = {Alexander F. Goncharov and Elena Bykova and Iskander Batyrev and Maxim Bykov and Huawei Chen and William Palfey and Mahmood Mohammad and Stella Chariton and Vitali Prakapenka and Jesse S. Smith},
journal= {arXiv preprint arXiv:2604.16641},
year = {2026}
}