We investigate the superconducting ternary lithium borohydride phase diagram at pressures of 0 and 200GPa using methods for evolutionary crystal structure prediction and linear-response calculations for the electron-phonon coupling. Our calculations show that the ground state phase at ambient pressure, LiBH4, stays in the Pnma space group and remains a wide band-gap insulator at all pressures investigated. Other phases along the 1:1:x Li:B:H line are also insulating. However, a full search of the ternary phase diagram at 200GPa revealed a metallic Li2BH6 phase, which is thermodynamically stable down to 100GPa. This {\em superhydride} phase, crystallizing in a Fm3ˉm space group, is characterized by six-fold hydrogen-coordinated boron atoms occupying the fcc sites of the unit cell. Due to strong hydrogen-boron bonding this phase displays a critical temperature of ∼ 100K between 100 and 200GPa. Our investigations confirm that ternary compounds used in hydrogen-storage applications are a suitable choice for observing high-Tc conventional superconductivity in diamond anvil cell experiments, and suggest a viable route to optimize the critical temperature of high-pressure hydrides.
@article{arxiv.1705.06977,
title = {Prediction of High-Tc conventional Superconductivity in the Ternary Lithium Borohydride System},
author = {Christian Kokail and Lilia Boeri and Wolfgang von der Linden},
journal= {arXiv preprint arXiv:1705.06977},
year = {2017}
}