中文摘要：

采用密度泛函理论框架下的平面波方法结合准谐近似,研究了Ge3N4的β相、w相和γ相在高温高压条件下的力学稳定性、相变点、电子结构和弹性性质。结果表明：γ相的抗剪切能力最强、刚度最大、属于超硬材料,β相具有最小的体弹模量、杨氏模量和G/B值、因此韧性和延性最好;w相和β相都属于延性相;而γ相则呈现出脆性,在30GPa后转变为延性材料。3种相都属于半导体,成键主要来自于N-2p轨道和Ge-4s、Ge-4p轨道的杂化;它们的结构能保持稳定是源于强烈的共价键;β相、w相和γ相分别属于Γ-A型、Γ-N型间接带隙和直接带隙半导体。研究发现,β→w相变对压强非常敏感,可以认为该相变是因压强的改变而引起的;w→γ相变伴随着晶胞体积的塌缩;同时,还成功地得到了β→w→γ相变的相界。

英文摘要：

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 ofβ-,w-andγ-Ge3N4 are investigated at high temperatures and pressures.Theγphase,which belongs to super-hard material,has the maximum rigidity and shear stress resistance.Theβphase has the minimum bulk modulus,Youngs modulus and G/Bratio.Theβphase has better ductility and tenacity than the other two phases.β-and w-Ge3N4 belong to ductile materials while theγphase shows a brittle manner.When the pressure exceeds 30 GPa,theγphase belongs to ductile materials too.β-,w-andγ-Ge3N4 are typical semiconductors,the bonding interactions are mainly contributed by the Ni-2p,Ge-4s and 4pbands.Theβ,wandγphases belong toΓ-A,Γ-N indirect band gap and direct band gap semiconductors,respectively.Theβ→w phase transition is sensitive to pressure.The w→γphase transition is accompanied by the shrinkage of volume.Meanwhile,the phase boundaries ofβ→w→γtransitions are also successfully obtained.