We have discovered a stoichiometric LiB with hexagonal boron layers by compressing known LiB0.9 with linear boron chains. The sp to sp 2 rebonding occurred at room temperature and moderate pressures above 21 GPa. The study was motivated by a long-standing prediction that LiB in the stable layered configuration could be a close analog to the MgB2 superconductor. Apparent stacking disorder in LiB and an evidenced stoichiometry shift in LiBy (down to y ≈ 0.75) made the materials' characterization a challenge. Ab initio modeling allowed us to establish LiBy's pressure-dependent composition and predict overlooked related stable structures. The synchrotron powder diffraction data indicates that synthesized LiB remains metastable under ambient pressure.

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