Abstract
Hydrogen-rich superhydrides are believed to be very promising high-Tc superconductors. Recent experiments discovered superhydrides at very high pressures, e.g. FeH5 at 130 GPa and LaH10 at 170 GPa. With the motivation of discovering new hydrogen-rich high-Tc superconductors at lowest possible pressure, here we report the prediction and experimental synthesis of cerium superhydride CeH9 at 80–100 GPa in the laser-heated diamond anvil cell coupled with synchrotron X-ray diffraction. Ab initio calculations were carried out to evaluate the detailed chemistry of the Ce-H system and to understand the structure, stability and superconductivity of CeH9. CeH9 crystallizes in a P63/mmc clathrate structure with a very dense 3-dimensional atomic hydrogen sublattice at 100 GPa. These findings shed a significant light on the search for superhydrides in close similarity with atomic hydrogen within a feasible pressure range. Discovery of superhydride CeH9 provides a practical platform to further investigate and understand conventional superconductivity in hydrogen rich superhydrides.
Highlights
Hydrogen-rich superhydrides are believed to be very promising high-Tc superconductors
Hydrides may satisfy all these conditions as the low mass of hydrogen results in high phonon frequency; covalent bonding is favourable for strong electron–phonon coupling; metallization under high pressure can result in high electronic density of states at the Fermi level[10]
The cerium sample and hydrogen gas were loaded into the sample chamber of the diamond anvil cell (DAC) and were kept at 9 GPa
Summary
Hydrogen-rich superhydrides are believed to be very promising high-Tc superconductors. Hydrides may satisfy all these conditions as the low mass of hydrogen results in high phonon frequency; covalent bonding is favourable for strong electron–phonon coupling; metallization under high pressure can result in high electronic density of states at the Fermi level[10]. Within this view the remarkable prediction and experimental confirmation of superconductivity at a record high Tc of 203 K under pressure of 150 GPa in H3S makes sense[14,15]. Most of the phases with Tc close to room temperature are predicted to have a clathrate structure with hydrogen forming a cage around metal atom (M)
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