中国高压科学技术高级研究中心Mao, Ho-Kwang团队近日研究了通向金属氢的超高压晶体通道。2025年5月14日，《自然》杂志发表了这一成果。

分子氢H₂在数兆巴压缩下的结构演化及其与原子金属氢的关系是凝聚态物理学中一个尚未解决的关键问题。尽管理论上已经提出了几十种晶体结构，但只有一种，即仅球形无序H₂的简单六方密堆积（hcp）结构，在实验中得到了证实。通过推进纳米聚焦同步加速器X射线探针，我们在这里报告了在212 GPa以上的压力下从hcp H₂到后hcp结构的转变，该结构具有六倍大的超晶胞，表示球形H₂转变为各种有序构型。 

基于该XRD结果的理论计算发现了空间群P62c中的时间平均结构模型具有球形无序H₂的交替层和由三个H₂分子结合形成的H₂三聚体（H₆）组成的新的石墨烯状层。这种超单体在之前的任何关于hcp后相的理论研究中都没有报道，但与许多具有混合层结构的理论模型接近。

hcp之外结构转变的证据确立了H₂分子在极端压力下聚合的趋势，为金属氢的分子到原子转变的性质提供了线索。考虑到光谱行为显示H₂的强烈振动和弯曲峰高达400 GPa，谨慎的做法是推测氢分子聚合会持续到金属化。

附：英文原文

Title: Ultrahigh-pressure crystallographic passage towards metallic hydrogen

Author: Ji, Cheng, Li, Bing, Luo, Jie, Zhao, Yongsheng, Liu, Yuan, Glazyrin, Konstantin, Bjrling, Alexander, Maral, Lucas A. B., Kahnt, Maik, Kalbfleisch, Sebastian, Liu, Wenjun, Gao, Yang, Wang, Junyue, Mao, Wendy L., Liu, Hanyu, Ma, Yanming, Ding, Yang, Yang, Wenge, Mao, Ho-Kwang

Issue&Volume: 2025-05-14

Abstract: The structural evolution of molecular hydrogen H2 under multi-megabar compression and its relation to atomic metallic hydrogen is a key unsolved problem in condensed-matter physics. Although dozens of crystal structures have been proposed by theory1,2,3,4, only one, the simple hexagonal-close-packed (hcp) structure of only spherical disordered H2, has been previously confirmed in experiments5. Through advancing nano-focused synchrotron X-ray probes, here we report the observation of the transition from hcp H2 to a post-hcp structure with a six-fold larger supercell at pressures above 212GPa, indicating the change of spherical H2 to various ordered configurations. Theoretical calculations based on our XRD results found a time-averaged structure model in the space group P62c with alternating layers of spherically disordered H2 and new graphene-like layers consisting of H2 trimers (H6) formed by the association of three H2 molecules. This supercell has not been reported by any previous theoretical study for the post-hcp phase, but is close to a number of theoretical models with mixed-layer structures. The evidence of a structural transition beyond hcp establishes the trend of H2 molecular association towards polymerization at extreme pressures, giving clues about the nature of the molecular-to-atomic transition of metallic hydrogen. Considering the spectroscopic behaviours that show strong vibrational and bending peaks of H2 up to 400GPa, it would be prudent to speculate the continuation of hydrogen molecular polymerization up to its metallization.

DOI: 10.1038/s41586-025-08936-w

Source: https://www.nature.com/articles/s41586-025-08936-w