Origin of enhanced chemical precompression in cerium hydride CeH${}_9$

Abstract

The rare-earth metal hydrides with clathrate structures have been highly attractive because of their promising high-$T_{\mathrm{c}}$ superconductivity at high pressure. Recently, cerium hydride CeH${}_9$ composed of Ce-encapsulated clathrate H cages was synthesized at much lower pressures of 80$-$100 GPa, compared to other experimentally synthesized rare-earth hydrides such as LaH${}_{10}$ and YH${}_6$. Based on density-functional theory calculations, we find that the Ce 5$p$ semicore and 4$f$/5$d$ valence states strongly hybridize with the H 1$s$ state, while a transfer of electrons occurs from Ce to H atoms. Further, we reveal that the delocalized nature of Ce 4$f$ electrons plays an important role in the chemical precompression of clathrate H cages. Our findings not only suggest that the bonding nature between the Ce atoms and H cages is characterized as a mixture of ionic and covalent, but also have important implications for understanding the origin of enhanced chemical precompression that results in the lower pressures required for the synthesis of CeH${}_9$.

arXiv comment6 pages, 6 figures

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