Study of the Electronic Structure, High-Pressure Elastic Property and Phase Stability of Germanium Nitride

Through the plane-wave method in the framework of density functional theory in combination with the quasi-harmonic approximation, the mechanical stability, phase boundary, electronic structures and elastic properties of β-, w- and γ-Ge₃N₄ are investigated at high temperatures and pressures.The γ phase, which belongs to super-hard material, has the maximum rigidity and shear stress resistance.The β phase has the minimum bulk modulus, Young's modulus and G/B ratio.The β phase has better ductility and tenacity than the other two phases.β- and w-Ge₃N₄ belong to ductile materials while the γ phase shows a brittle manner.When the pressure exceeds 30 GPa, the γ phase belongs to ductile materials too.β-, w- and γ-Ge₃N₄ are typical semi-conductors, the bonding interactions are mainly contributed by the Ni-2p, Ge-4s and 4p bands.The β, w and γ phases belong to Γ-A, Γ-N indirect band gap and direct band gap semiconductors, respectively.The β→w phase transition is sensitive to pressure.The w→γ phase transition is accompanied by the shrinkage of volume.Meanwhile, the phase boundaries of β→w→γ transitions are also successfully obtained.