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

TL;DR

This study uses first-principles calculations to analyze the thermodynamic stability of various Li-B-C compounds, providing insights into their synthesis conditions and stability, and identifying more favorable but still unstable configurations.

Contribution

It offers a comprehensive first-principles analysis of Li-B-C phases, including stability assessments and the identification of more favorable configurations through evolutionary optimization.

Findings

LiBC's delithiation conditions estimated from chemical potential calculations.

Metastable BC₃ polymorphs with honeycomb and diamond-like structures observed.

Newly reported BC₃, LiBC₃, and Li₂B₂C phases are unstable; more favorable configurations are identified.

Abstract

Prediction of high-$T_{\rm{c}}$ 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.