LAUSR

Abstract The fascinating properties and widely applications of boron-rich compounds induce the research interest in this work. Herein, a first-principles calculations was performed to investigate the effects of pressure on the structural, mechanical and dynamical properties of the newly discovered orthorhombic sodium boride with I212121 and Imma symmetry (denoted as I212121–Na2B30 and Imma-Na2B30 hereafter). Results show that the I212121–Na2B30 is energetically more favorable than the Imma-Na2B30 with increasing pressure, suggesting that more uniform charge transfer in I212121–Na2B30 than Imma-Na2B30. The mechanical calculations indicate that both phases of Na2B30 are mechanical stability and possess superior mechanical properties under pressure. The Vickers hardness values of Na2B30 are estimated using three different models, the results show that both phases of Na2B30 are hard materials (Hv ​> ​20 ​GPa) under pressure, and the hardness value of I212121–Na2B30 is higher than the Imma-Na2B30, which mainly originates from the strong B–B covalent bonding and the cages formed by B12 icosahedra unit. Further analysis of brittleness and ductility show that both phases of Na2B30 are intrinsically brittleness and high pressure can reduce its brittleness. Finally, the phonon calculation noted that the two phases of Na2B30 are dynamically stable at 0 ​GPa, but the instability exhibited when the pressure increased to ~16 ​GPa for the I212121–Na2B30, and the maximum imaginary frequency decreases with the increase of pressure. These results can provide a deeper insight into physical properties of boron-rich compounds, and thus are useful to design and synthesis superhard materials in the future.