Stability and bonding nature of clathrate H cages in a near-room-temperature superconductor LaH10

Abstract

Lanthanum hydride (LaH10) with a sodalitelike clathrate structure was experimentally synthesized to exhibit a near-room-temperature superconductivity under megabar pressures. Based on first-principles density-functional theory calculations, we reveal that the metal framework of La atoms has excess electrons at interstitial regions. Such anionic electrons are easily captured to form a stable clathrate structure of H cages. We thus propose that the charge transfer from La to H atoms is mostly driven by the electride property of the La framework. Furthermore, the interaction between La atom and H cage induces a delocalization of La 5p semicore states to hybridize with the H 1s state. Consequently, the bonding nature of LaH10 is characterized as a mixture of ionic and covalent bonding between La atom and H cage. Our findings demonstrate that anionic and semicore electrons play important roles in stabilizing clathrate H cages in LaH10, which can be broadly applicable to other compressed rare-earth hydrides with clathrate structures.