Understanding the crystal structure of solid hydrogen under ultrahigh pressure

OCT 23, 2020

Scientists obtain high-quality X-ray diffraction data about solid hydrogen under extreme pressures of up to 254 GPa, paving the way for studying the crystal structure of hydrogen at higher pressures and eventually testing metallic hydrogen.

Aili McConnon

DOI: 10.1063/10.0002412

Understanding the crystal structure of solid hydrogen under ultrahigh pressure internal name — Understanding the crystal structure of solid hydrogen under ultrahigh pressure lead image

Very high pressures and temperatures enable new phenomena, such as creating novel materials and understanding underlying crystal structures. As a result, scientists have increasingly focused on research under extreme conditions. Ji et al. examined solid hydrogen to understand how to measure its crystal structure under ultrahigh pressure.

The researchers developed methods which successfully overcome the difficulties in measuring the crystal structure of hydrogen at above 2,000,000 atmospheric pressures. As a result, they obtained high quality X-ray diffraction (XRD) data of solid hydrogen at extreme pressures of up to 254 GPa at room temperature.

“In our study, we target solid hydrogen to understand how to measure its crystal structure under ultrahigh pressure. In fact, our developed methods can be used in any other materials under ultrahigh pressure,” said author Cheng Ji.

The scientists generated high pressure using a diamond anvil cell, which uses the needle tips of diamond to squeeze the material being studied. By optimizing the sample preparation techniques with a composite gasket, they were able to contain the sample to the target pressure and obtain high-quality, clear data. Finally, they developed advanced diagnostic methods by using a nano-focus X-ray beam and a specially designed collimation tool to further improve data quality.

“Our findings provide a powerful solution for better studying novel materials at ultrahigh pressure based on XRD methods,” said Ji.

The researchers will focus next on crystallographic studies of metallic hydrogen and polymeric nitrogen and continue to develop the experimental techniques for better performing ultrahigh pressure XRD studies.

Source: “Crystallography of low Z material at ultrahigh pressure: Case study on solid hydrogen,” by Cheng Ji, Bing Li, Wenjun Liu, Jesse S. Smith, Alexander Bjorling, Arnab Majumdar, Wei Luo, Rajeev Ahuja, Jinfu Shu, Junyue Wang, Stanislav Sinogeikin, Yue Meng, Vitali B. Prakapenka, Eran Greenberg, Ruqing Xu, Xianrong Huang, Yang Ding, Alexander Soldatov, Wenge Yang, Guoyin Shen, Wendy L. Mao, and Ho-Kwang Mao, Matter and Radiation at Extremes (2020). The article can be accessed at https://aip.scitation.org/doi/full/10.1063/5.0003288 . This paper is part of the High Pressure Science Collection, learn more here .