Predicted High-Pressure Hot Superconductivity in Li$_2$CaH$_{16}$ and Li$_2$CaH$_{17}$ Phases that Resemble the Type-II Clathrate Structure

TL;DR

This study predicts high-temperature superconductivity in novel Li-Ca-H phases with cage-like structures at high pressures, indicating potential for hot superconductors with critical temperatures up to 370 K.

Contribution

The paper introduces two new high-pressure hydride phases with cage-like structures related to Type-II clathrates, predicting their superconducting properties using density functional theory.

Findings

Li₂CaH₁₆ has a predicted Tc of 330 K at 350 GPa.

Li₂CaH₁₇ has a predicted Tc of 370 K at 300 GPa.

Li₂CaH₁₇ remains superconducting down to 160 GPa with Tc of 205 K.

Abstract

High-temperature high-pressure superconducting hydrides are typically characterized by cage-like hydrogenic lattices filled with electropositive metal atoms. Here, density functional theory based evolutionary crystal structure searches find two phases that possess these geometric features and are related to the Type-II clathrate structure. In these $Fd\overline{3}m$ Li$_2$CaH$_{16}$ and $R\overline{3}m$ Li$_2$CaH$_{17}$ phases the calcium atom occupies the larger cage and the lithium atom the smaller one. The highest superconducting critical temperatures predicted within the isotropic Eliashberg formalism, 330~K at 350~GPa for $Fd\overline{3}m$ Li$_2$CaH$_{16}$ and 370~K at 300~GPa for $R\overline{3}m$ Li$_2$CaH$_{17}$, suggest these structures fall in the class of high-energy-density quantum materials known as hot superconductors. As pressure is lowered the cage-like lattices distort with the emergence of quasimolecular hydrogenic motifs; nonetheless Li$_2$CaH$_{17}$ is predicted to be superconducting down to 160~GPa at 205~K.