Unexpected compound reformation in the dense selenium-hydrogen system

• Published in: Communications materials Vol. 6; no. 1; pp. 193 - 7
• Main Authors: Hu, Huixin, Kuzovnikov, Mikhail A., Shuttleworth, Hannah A., Marqueño, Tomas, Yan, Jinwei, Osmond, Israel, Gorelli, Federico A., Gregoryanz, Eugene, Dalladay-Simpson, Philip, Ackland, Graeme J., Peña-Alvarez, Miriam, Howie, Ross T.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.12.2025; Nature Publishing Group; Nature Portfolio
• Subjects: 639/301/119/1002; 639/638/440/94; 639/766/119/2795; Chemistry and Materials Science; Decomposition; Density functional theory; Diamond anvil cells; High pressure; High temperature; Hydrides; Hydrogen; Interstices; Lasers; Materials Science; Molecular chains; Phase transitions; Room temperature; Selenium; Spectrum analysis; Superconductivity
• ISSN: 2662-4443; 2662-4443
• DOI: 10.1038/s43246-025-00899-9

The H 2 Se molecule and the van der Waals compound (H 2 Se) 2 H 2 are both unstable upon room temperature compression, dissociating into their constituent elements above 22 GPa. Through a series of high pressure-high temperature diamond anvil cell experiments, we report the unexpected formation of a novel compound, SeH 2 (H 2 ) 2 at pressures above 94 GPa. X-ray diffraction reveals the metallic sublattice to adopt a tetragonal ( I 4 1 / a m d ) structure with density functional theory calculations finding a small distortion due to the orientation of H 2 molecules. The structure comprises of a network of zig-zag H-Se chains with quasi-molecular H 2 molecular units hosted in the prismatic Se interstices. Electrical resistance measurements demonstrate that SeH 2 (H 2 ) 2 is non-metallic up to pressures of 148 GPa. Investigations into the Te-H system up to pressures of 165 GPa and 2000 K yielded no compound formation. The combined results suggest that the high pressure phase behavior of each chalcogen hydride is unique and more complex than previously thought. High-pressure studies of chalcogen hydrides reveal complex phase behaviors, challenging existing assumptions about their stability and composition. Here, the authors discover a novel compound, SeH 2 (H 2 ) 2 , at pressures above 94 GPa, characterized by a unique tetragonal structure, highlighting the intricate nature of high-pressure chemistry and its implications for material science.