Ternary superconducting hydrides in the La-Mg-H system

TL;DR

This study explores the La-Mg-H ternary system under high pressure, discovering new superconducting hydrides with high critical temperatures and demonstrating advanced methods for predicting complex crystal structures.

Contribution

The paper reports the discovery of new stable and metastable ternary and binary hydrides in the La-Mg-H system using evolutionary algorithms, advancing the understanding of high-pressure superconductors.

Findings

Identified stable ternary superconducting hydrides with high T_c values.

Predicted novel binary hydrides stable at various pressures.

Developed methods to efficiently explore large chemical spaces.

Abstract

Ternary or more complex hydrogen-rich hydrides are the main hope of reaching room-temperature superconductivity at high pressures. Their chemical space is vast and its exploration is challenging. Here we report the investigation of the La-Mg-H ternary system using the evolutionary algorithm USPEX at pressures on the range 150-300 GPa. Several ternary superconducting hydrides were found, including thermodynamically stable $P6/mmm$-LaMg$_{3}$H$_{28}$ with $T_{\mathrm{C}}=164$ K at 200 GPa, $P/2m$-LaMgH$_8$, $C2/m$-La$_2$MgH$_{12}$ and $P2/m$-La$_3$MgH$_{16}$. In addition, novel binary hydrides were predicted to be stable at various pressures, such as $Cm$-Mg$_6$H$_{11}$, $P1$-MgH$_{26}$, $Fmm2$-MgH$_{30}$, $P1$-MgH$_{38}$ and $R\overline{3}m$-LaH$_{13}$. We also report several novel low-enthalpy metastable phases, both ternary and binary ones. Finally, we demonstrate important methods of exploring very large chemical spaces and show how they can improve crystal structure prediction.