Thermodynamic stability of Li-B-C compounds from first principles

Abstract

Prediction of high-$T_{\mathrm{c}}$ superconductivity in hole-doped Li${}_x$BC two decades ago has brought about an extensive effort to synthesize new materials with honeycomb B-C layers, but the thermodynamic stability of Li-B-C compounds remains largely unexplored. In this study, we use density functional theory to characterize well-established and recently reported Li-B-C phases. Our calculation of the Li chemical potential in Li${}_x$BC helps estimate the ($T$,$P$) conditions required for delithiation of the LiBC parent material, while examination of B-C phases helps rationalize the observation of metastable BC${}_3$ polymorphs with honeycomb and diamond-like morphologies. At the same time, we demonstrate that recently reported BC${}_3$, LiBC${}_3$, and Li${}_2$B${}_2$C phases with new crystal structures are both dynamically and thermodynamically unstable. With a combination of evolutionary optimization and rational design, we identify considerably more natural and favorable Li${}_2$B${}_2$C configurations that, nevertheless, remain above the thermodynamic stability threshold.

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• Machine-learning Guided Search for Phonon-mediated Superconductivity in Boron and Carbon Compounds
• High-$T_{\mathrm{c}}$ Ag${}_x$BC and Cu${}_x$BC superconductors accessible via topochemical reactions
• Possible high thermoelectric power factor in alkali-metal-intercalated BC${}_3$: anisotropic multiple valleys originating from the van Hove singularity of graphene