First Principles Study on Mechanical Properties of Superhard α-Ga Boron

The mechanical properties and intrinsic hardness of the α-Ga boron phase (α-Ga-B) are studied by using the combination of first-principles calculations and a semiempirical macroscopic hardness model. It is found that α-Ga-B is mechanically stable and possesses higher bulk/shear modulus as compared with γ-B₂₈, a newly discovered high-pressure boron phase. The theoretical hardness of α-Ga-B is estimated to be 45 GPa, which is much higher than 38 GPa for γ-B₂₈. The results strongly indicate that α-Ga-B is a potential superhard boron phase. To further obtain insight into the superhard nature of α-Ga-B, we simulate stress–strain curves under tensile and shear deformation. Meanwhile, the microscopic mechanism driving the tensile and shear deformation modes in α-Ga-B is discussed in detail.