High-Pressure Synthesis of Seven Lanthanum Hydrides with a Significant Variability of Hydrogen Content

TL;DR

This study reveals a diverse range of lanthanum hydrides synthesized under high pressure, highlighting variability in hydrogen content and structural complexity, which impacts the search for high-temperature superconductors.

Contribution

The paper reports the discovery and structural characterization of seven different lanthanum hydrides, expanding understanding of their chemical diversity under high pressure.

Findings

Seven lanthanum hydrides identified and structurally characterized.

Significant variability in hydrogen content among synthesized hydrides.

Challenges in identifying superconducting phases due to phase heterogeneity.

Abstract

The lanthanum-hydrogen system has attracted significant attention following the report of superconductivity in LaH10 at near-ambient temperatures and high pressures. Here, we present the results of our single-crystal X-ray diffraction studies on this system, supported by density functional theory calculations, which reveal an unexpected chemical and structural diversity of lanthanum hydrides synthesized in the range of 50 to 180 GPa. Seven lanthanum hydrides were produced, LaH3, LaH~4, LaH4+{\delta}, La4H23, LaH6+{\delta}, LaH9+{\delta}, and LaH10+{\delta}, and the atomic coordinates of lanthanum in their structures determined. The regularities in rare-earth element hydrides unveiled here provide clues to guide the search for other synthesizable hydrides and candidate high-temperature superconductors. The hydrogen content variability in lanthanum hydrides and the samples' phase heterogeneity underline the challenges related to assessing potentially superconducting phase(s) and the nature of electronic transitions in high-pressure hydrides.