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Updated: Sep 24, 2025

Quantification of Hydrogen Concentrations in Surface and Interface Layers and Bulk Materials through Depth Profiling with Nuclear Reaction Analysis

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Published on: March 29, 2016

New possible candidate structure for phase IV of solid hydrogen.

Guo-Jun Li^1,2, Yun-Jun Gu², Zhi-Guo Li²

¹College of Physics, Sichuan University Chengdu 610065 China xrchen@scu.edu.cn.

|May 6, 2022

Summary

Researchers propose a new orthorhombic structure, Ama2, for solid hydrogen phase IV. This structure better matches experimental Raman frequencies, resolving discrepancies in high-pressure hydrogen research.

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Quantification of Hydrogen Concentrations in Surface and Interface Layers and Bulk Materials through Depth Profiling with Nuclear Reaction Analysis

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Atomically Traceable Nanostructure Fabrication

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Published on: July 17, 2015

Area of Science:

Condensed Matter Physics
Materials Science
High-Pressure Physics

Background:

Solid hydrogen exhibits complex phase behavior under high pressure.
Only the structure of phase I is definitively known, leaving other phases, like phase IV, poorly understood.

Purpose of the Study:

To investigate the phase space of solid hydrogen at 200-500 GPa.
To identify potential candidate structures for phase IV.
To resolve discrepancies between theoretical calculations and experimental vibrational data.

Main Methods:

Particle swarm optimization combined with first-principles simulations.
Density functional perturbation theory for vibrational frequency calculations.
First-principles molecular dynamics for pressure dependence analysis.

Main Results:

A novel orthorhombic structure, Ama2, is proposed as a candidate for phase IV.
Ama2 exhibits a 'mixed structure' with distinct layers, differing from the Pc structure.
Calculated vibrational frequencies of Ama2 show improved agreement with experimental Raman and infrared data.
The pressure dependence of Ama2's low-frequency Raman vibrons aligns better with experimental observations.

Conclusions:

The Ama2 structure provides a better explanation for experimental vibrational spectra of phase IV solid hydrogen.
The weakly bonded layers in Ama2 resemble those in the C2/c structure, confirming experimental findings.
This study advances the understanding of high-pressure solid hydrogen phases and resolves long-standing discrepancies.