Superconductivity in CH4 and BH4- Containing Compounds Derived from the High-Pressure Superhydrides

TL;DR

This study uses density functional theory to predict new superconducting compounds derived from high-pressure superhydrides, identifying stable phases with Tcs above 40 K and analyzing their stability and properties under various pressures.

Contribution

It introduces novel ternary compounds based on LaH10 with boron or carbon substitution, predicting their stability and superconducting properties using advanced computational methods.

Findings

KB2H8 predicted to have Tc above 40 K at high pressure.

Stable phases like KB2H8, RbB2H8, CsB2H8 identified at mild pressures.

Quantum anharmonic effects significantly influence the properties of KB2H8.

Abstract

Inspired by the synthesis of the high-pressure Fm-3m LaH10 superconducting superhydride, systematic density functional theory (DFT) calculations are performed to study ternaries that could be derived from it by replacing two of the hydrogen atoms with boron or carbon and varying the identity of the electropositive element. Though many of the resulting alkali-metal and alkaline-earth MC2H8 phases are predicted to be dynamically stable at mild pressures, their superconducting critical temperatures (Tcs) are low because their metallicity results from the filling of an electride-like band. Substitution with a trivalent element leads to phases with substantial metal d-character at the Fermi level whose Tcs are typically above 40 K. Among the MB2H8 phases examined, KB2H8, RbB2H8 and CsB2H8 are predicted to be dynamically stable at very mild pressures, and their stability is rationalized by a DFT-Chemical Pressure analysis that elucidates the role of the M atom size. Quantum anharmonic effects strongly affect the properties of KB2H8, the highest predicted Tc compound, near 10 GPa, but molecular dynamics simulations reveal it would decompose below its Tc at this pressure. Nonetheless, at ca. 50 GPa KB2H8 is predicted to be thermally stable with a superconducting figure of merit surpassing that of the recently synthesized LaBeH8.