【Frontiers of HaiChuan Chemical Technology】Amazing! ! ! Chinese scientists were the first to “see” the finest structure of solid hydrogen

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Chinese scientists were the first to “see” the finest structure of solid hydrogen. Under normal temperature and pressure, hydrogen exists in a gaseous state. Under high pressure, hydrogen crystallizes into a solid. The atomic arrangement of solid hydrogen under ultra-high pressure has long remained an unsolved mystery.   On May 14, 2025, the internationally renowned academic journal Nature published a major breakthrough: an international team led by Chinese scientists used X-ray nanoprobes to observe for the first time the complex crystal structure of solid hydrogen. This is the most precise structure of solid hydrogen in the world today.   The increase in pressure causes the crystal structure of hydrogen to become more complex. “Molecules of gaseous hydrogen are randomly scattered throughout space. As the pressure increases to 5 GPa, hydrogen molecules arrange themselves in layers like dominoes, forming solid hydrogen. As the pressure increases further (212–245 GPa), some hydrogen atoms arrange themselves in a honeycomb pattern, resulting in a more complex structure for solid hydrogen: checkerboard-like elements and honeycomb structures stacked on top of each other. ”Ji Cheng, the first author of the paper and a researcher at the Beijing High Pressure Science Research Center, said.   Why do we need to “see” solid hydrogen? “Metallic hydrogen possesses an extremely high energy density, making it an ideal material for hydrogen nuclear fusion; it holds great potential for application and strategic importance, and is referred to as the ‘holy grail of high-pressure physics’. To find metallic hydrogen, studying solid hydrogen is an essential step. ”Ma Heguang, a high-pressure physicist and foreign academician of the Chinese Academy of Sciences, said.   If metallic hydrogen is the “Holy Grail,” then the structure of solid hydrogen under high pressure is akin to the pedestal of that Holy Grail. Chinese scientists were the first to “see” solid hydrogen in its fine-structure state, which exists under high pressure right after gas hydrogen turns into solid hydrogen and before metallic hydrogen forms.   Mao Heguang explained that Nobel Prize in Physics laureates such as Wagner predicted in 1935 that hydrogen would turn into metallic hydrogen under extremely high pressures. Later, physicists proposed that the pressure required to metallize hydrogen is as high as 500 GPa – which is equivalent to the force exerted by a giant jet plane parked on the tip of a needle.   In the laboratories of the Beijing High Pressure Science Research Center, the fractured diamond samples that have been tested are numbered, labeled, and stored. The image shows some of the fractured diamond samples after the experiment was completed, with the box lid removed. (Photo provided by the interviewee) “Observing metallic hydrogen is extremely difficult, as the ultra-high pressure conditions required for hydrogen metallization are very stringent.” We bring two super-sharp diamond tips together, tip-to-tip, to compress the hydrogen molecules in between. High-intensity X-rays are used to penetrate the diamond and illuminate the high-pressure hydrogen; the interaction between these X-rays and the high-pressure hydrogen is akin to taking a ‘photo’ of the solid hydrogen, allowing us to see how the atoms are arranged. ”Jicheng said.   “The study of crystal structures should be at the core of research on metallic hydrogen.” Because the peculiar properties of metallic hydrogen depend on its unique atomic arrangement. ”Mao Heguang said that this discovery provides crucial evidence for understanding the formation pathways and mechanisms of metallic hydrogen.