Observation of the most H2-dense filled ice under high pressure

Year: 2023

Authors: Ranieri U., Di Cataldo S., Rescigno M., Monacelli L., Gaal R., Santoro M., Andriambariarijaona L., Parisiades P., De Michele C., Bove LE.

Autors Affiliation: Sapienza Univ Roma, Dipartimento Fis, I-00185 Rome, Italy; Univ Edinburgh, Ctr Sci Extreme Condit, Edinburgh EH9 3FD, Scotland; Univ Edinburgh, Sch Phys & Astron, Edinburgh EH9 3FD, Scotland; Tech Univ Wien, Inst Festkorperphys, A-1040 Vienna, Austria; Ecole Polytech Fed Lausanne, Inst Phys, Lab Quantum Magnetism, CH-1015 Lausanne, Switzerland; Ecole Polytech Fed Lausanne, Theory & Simulat Mat, CH-1015 Lausanne, Switzerland; Ecole Polytech Fed Lausanne, Natl Ctr Computat Design & Discovery Novel Mat, CH-1015 Lausanne, Switzerland; Ist Nazl Ott Consiglio Nazl Ric CNR INO, I-50019 Sesto Fiorentino, Italy; LENS, European Lab Nonlinear Spect, I-50019 Sesto Fiorentino, FI, Italy; Sorbonne Univ, Inst Mineral Phys Mat & Cosmochim, UMR CNRS 759, F-75252 Paris, France.

Abstract: Hydrogen hydrates are among the basic constituents of our solar system’s outer planets, some of their moons, as well Neptune-like exo-planets. The details of their high-pressure phases and their thermodynamic conditions of formation and stability are fundamental information for establishing the presence of hydrogen hydrates in the interior of those celestial bodies, for example, against the presence of the pure components (water ice and molecular hydrogen). Here, we report a synthesis path and experimental observation, by X-ray diffraction and Raman spectroscopy measurements, of the most H2-dense phase of hydrogen hydrate so far reported, namely the compound 3 (or C3). The detailed characterisation of this hydrogen-filled ice, based on the crystal structure of cubic ice I (ice Ic), is performed by comparing the experimental observations with first-principles calculations based on density functional theory and the stochastic self-consistent harmonic approximation. We observe that the extreme (up to 90 GPa and likely beyond) pressure stability of this hydrate phase is due to the close-packed geometry of the hydrogen molecules caged in the ice Ic skeleton.

Journal/Review: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA

Volume: 120 (52)      Pages from: e2312665120-1  to: e2312665120-8

More Information: We acknowledge the European Synchrotron Radiation Facility for provision of synchrotron radiation facilities at the ID15B beam line under proposal number HC-5060 and assistance from M. Hanfland, D. Comboni, and G. Garbarino. Preliminary measurements for this project were carried out at the ID27 beam line, and we thank M. Mezouar and A. Pakhomova. We thank the ANR-23-CE30-0034 EXOTIC-ICE. We acknowledge funding through the Swiss National Fund (FNS) grant EXOTIC-ICES n 212889, PRIN 2022 NRBLPT, and from progetto di ateneo RM120172B8E7BC07. S.D.C. acknowledges computational resources from CINECA, proj. IsC90-HTS-TECH and IsC99-ACME-C, and the Vienna Scientific Cluster, proj. 71754 TEST. L.M. acknowledges computational resources from CSCS, Piz Daint, under project s1192 and the grant Marie Sklodowska-Curie Actions Individual Fellowship (MSCA IF) , project codename THERMOH. We thank Werner F. Kuhs, Andrzej Falenty, Dirk Wallacher, and Alain Polian for help during sample preparation and Lewis Conway for kindly sharing his code for structural analysis. S.D.C. thanks Guang-Rui Qian for the useful discussion.
KeyWords: clathrate hydrates; phase transitions; pressure; Raman | ab; initio simulations
DOI: 10.1073/pnas.2312665120

Citations: 1
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