Surface melting-driven hydrogen absorption for high-pressure polyhydride synthesis

• 成果类型: Article
• 署名作者: Sato, Ryuhei; Conway, Lewis J.; Zhang, Di; Pickard, Chris J.; Akagi, Kazuto; Sau, Kartik; Li, Hao; Orimo, Shin - ichi
• 署名单位: Tohoku University; University of Tokyo; University of Cambridge; National Institute of Advanced Industrial Science & Technology (AIST); Tohoku University; Tohoku University
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-8726
• DOI: 10.1073/pnas.2413480122
• 发表日期: 2025-06-03
• 关键词: total-energy calculations; molecular-dynamics; lanthanum; hydrides

摘要

The synthesis of new polyhydrides with high superconducting Tc is challenging owing to the high pressures and temperatures required. In this study, we used machine-learning potential molecular dynamics simulations to investigate the initial stage of polyhydride formation in calcium hydrides. Upon contact with high-pressure H2, the surface of CaH2 melts, leading to CaH4 formation. This surface melting proceeds via CaH4 liquid phase as an intermediate state. High pressure reduces not only the hydrogenation (CaH2(s) + H2(l) <-> CaH4(s)) enthalpy but also the enthalpy for liquid polyhydride formation (CaH2(s) + H2(l) <-> CaH4(l)). Consequently, this surface melting process becomes more favorable than the fusion of the polyhydride bulk. Thus, high pressure not only shifts the equilibrium toward the polyhydride product but also lowers the activation energy, thereby promoting the hydrogenation reaction. From these thermodynamic insights, we propose structure-search criteria for polyhydride synthesis that are both computationally effective and experimentally relevant. These criteria are based on bulk properties, such as polyhydride (product) melting temperature and pressure-dependent hydrogenation enthalpy, readily determined through supplementary calculations during structure prediction workflows.