Pressure-induced ternary Li-Mn-B compounds: A first-principles study

B-rich metal compounds have garnered significant attention due to their diverse polymeric boron structures and versatile properties including high melting temperature, exceptional hardness, and superconductivity. In this paper, we systematically investigate the ternary phase diagram of the Li-Mn-B system at 0--100 GPa, employing a combination of crystal structure prediction methods and first-principles calculations. We identify five pressure-stabilized compounds with stoichiometries of ${\mathrm{Li}}_{2}\mathrm{Mn}{\mathrm{B}}_{2}, \mathrm{LiMn}{\mathrm{B}}_{3}, \mathrm{LiMn}{\mathrm{B}}_{4}, {\mathrm{Li}}_{2}\mathrm{Mn}{\mathrm{B}}_{8}$, and $\mathrm{LiMn}{\mathrm{B}}_{10}$. These pressure-induced compounds can be recovered to ambient pressure conditions. Notably, the boron atoms in these compounds exhibit diverse polymerization patterns, forming structures such as dimers, zigzag chains, ribbons, kagome lattices, and three-dimensional channel frameworks. The five Li-Mn-B compounds are potential hard materials, with $\mathrm{LiMn}{\mathrm{B}}_{4}$ standing out with a remarkable hardness value of 39.47 GPa. $\mathrm{LiMn}{\mathrm{B}}_{4}$ and $\mathrm{LiMn}{\mathrm{B}}_{10}$ are indirect semiconductors with band gaps of 0.92 and 0.64 eV, respectively. Notably, $\mathrm{LiMn}{\mathrm{B}}_{10}$ exhibits a lower effective mass than silicon, superior solar cell efficiency compared with silicon, and a work function comparable with that of silicon. These properties highlight the considerable potential of $\mathrm{LiMn}{\mathrm{B}}_{10}$ as a viable material for photovoltaic applications. ${\mathrm{Li}}_{2}\mathrm{Mn}{\mathrm{B}}_{8}$ is predicted to be a superconductor with a critical temperature of 15 K at 50 GPa. When the pressure is reduced to 0 GPa, ${\mathrm{Li}}_{2}\mathrm{Mn}{\mathrm{B}}_{8}$ displays antiferromagnetic properties. $\mathrm{LiMn}{\mathrm{B}}_{3}$ is a suitable precursor to obtain a ${\mathrm{B}}_{20}$-caged structure with remarkable superconductivity at ambient pressure, reaching a ${T}_{\mathrm{c}}$ of 31 K. In this paper, we provide comprehensive insights into the ternary phase diagram of the Li-Mn-B system at high pressure, elucidating the formation of various stable compounds with intriguing properties.