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arXiv · 2604.16641

Two New Molecular Nitrogen Phases near Megabar Pressures

Alexander F. Goncharov·Elena Bykova·Iskander Batyrev·Maxim Bykov·Huawei Chen·William Palfey·Mahmood Mohammad·Stella Chariton·Vitali Prakapenka·Jesse S. Smith
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Abstract

Molecular nitrogen exhibits remarkable structural diversity near the polymeric transition, where multiple phases are metastable. Here, we report two new molecular phases. The first, $t\zeta$-N$_2$, is a polytype of monoclinic $C2/c$ $\zeta$-N$_2$, characterized by a tripled $c$ axis and 96 atoms per unit cell. The second, $\xi$-N$_2$, 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 $\zeta$-N$_2$ 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 $t\zeta$-N$_2$ phase likely corresponds to the previously reported $\kappa$-N$_2$ phase.

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Alexander F. Goncharov, Elena Bykova, Iskander Batyrev, Maxim Bykov, Huawei Chen, William Palfey, Mahmood Mohammad, Stella Chariton, Vitali Prakapenka, Jesse S. Smith. 2026-04-17. Two New Molecular Nitrogen Phases near Megabar Pressures. https://arxiv.org/abs/2604.16641

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