Rational Design of Superconducting Metal Hydrides via Chemical Pressure Tuning

TL;DR

This paper uses a computational method to understand and predict how chemical pressure influences the structure and superconducting properties of metal hydrides, aiming to guide the design of higher-$T_c$ superconductors.

Contribution

It introduces the DFT-CP method to explain structural stability and predicts new superconducting phases in the Y-X-H system based on chemical pressure effects.

Findings

Large metal atoms induce structural distortions affecting $T_c$.

Stability of LaH$_{10}$ and LaBH$_8$ is linked to hydrogen and boron stuffing.

Predicted new ternary phases with potential superconductivity at low pressures.

Abstract

The high critical superconducting temperatures ($T_c$s) of metal hydride phases with clathrate-like hydrogen networks have generated great interest. Herein, we employ the Density Functional Theory-Chemical Pressure (DFT-CP) method to explain why certain electropositive elements adopt these structure types, whereas others distort the hydrogenic lattice, thereby decreasing the $T_c$. The progressive opening of the H$_{24}$ polyhedra in MH$_6$ phases is shown to arise from internal pressures exerted by large metal atoms, some of which may favor an even higher hydrogen content that loosens the metal atom coordination environments. The stability of the LaH$_{10}$ and LaBH$_8$ phases is tied to stuffing of their shared hydrogen network with either additional hydrogen or boron atoms. The predictive capabilities of DFT-CP are finally applied to the Y-X-H system to identify possible ternary additions yielding a superconducting phase stable to low pressures.