Tuning dimensionality in binary Li-B compounds and evaluating thermodynamic vs kinetic stability under pressure

The binary phase diagram of the light elements lithium and boron features an intriguing phase with a finite range of stability, LiB$_{\mathrm{x}}$ with 0.8$\le $x$\le $1.0. The experimental hexagonal structure contains two incommensurate sub-lattices, a hexagonal lithium network, and an array of linear boron chains. An alternative structure of almost equal energy is inspired by the AlB$_{\mathrm{2}}$ structure type, and contains graphitic boron sheets interspersed by trigonal lithium layers. We present results from a computational study on this system, at atmospheric and elevated pressures. We model the tunable atomic composition and predict the disappearance of the finite stability range of LiB$_{\mathrm{x}}$ at P$=$40GPa, where layered structures become more stable than chain-like structures across the entire composition range. Kinetic barriers are estimated and are predicted to facilitate the recovery of phases synthesized at high pressure. Up to P$=$70GPa, all stable structures are metallic, and trends of their electronic and dynamic properties will be discussed. At P\textgreater 70GPa, structure searches reveal that stoichiometric 1:1-LiB is most stable in the NaTl structure, with a diamondoid boron network, and becomes an insulator. The Zintl-Klemm concept helps understand the different structural choices under pressure.