【摘要】 利用基于密度泛函理论(Density functional theory,DFT)的广义梯度近似(Generalized gradient approximation,GGA)研究C掺杂Mg(B1-xCx)2晶体的电子结构和弹性性质。计算所得晶格参数和平衡态体积与实验结果符合较好。能带结构和态密度的研究结果表明,随着C掺杂量增加,费米能级附近Γ点、A点的能量EΓ(σ)、EA(σ)和费米能级处的态密度N(EF)减小,这与超导转变温度TC随C掺杂量增加而减小的实验结果一致。由Voigt、Reuss和Hill’s(VRH)近似计算得到的单晶弹性常数推导出多晶的弹性常数,结果表明随C掺杂量增加,Mg(B1-xCx)2晶体的体弹性模量单调地增加(可压缩系数单调地减小);泊松比ν和体积弹性模量/剪切弹性模量(BH/GH)的值先是较大幅度减小,而后略有增加;Mg(B1-xCx)2的泊松比远小于1/3,BH/GH的值小于材料的脆性和延展性的临界判据参数1.75,表明Mg(B1-xCx)2晶体是脆性化合物。更多还原

【Abstract】 The electronic structure and elastic properties of C doping Mg(B1-xCx)2 are studied by generalized gradient approximation(GGA) based on density functional theory(DFT) were studied.The calculated lattice parameters and equilibrium volumes are in good agreement with the available experimental data.The investigation results of energy band structure and the density of state(DOS) show that the energy EΓ(σ),EA(σ) of the point Γ and A near the Fermi level,and N(EF) at the Fermi level decrease with the increasing of the doping C;and these results are consistent with the results of experiment of superconductor transition temperature,Tc,being decreased with the increase of C dopant.Single-crystal elastic constants are calculated and the polycrystalline elastic modules are estimated according to Voigt,Reuss and Hill’s approximations(VRH).The results show that the bulk modules increase monotonously and the values of Possion ratio as well as the ratio of bulk modulus for Hill’s model(BH)/shearing modulus of Hill’s model(BG) decrease first and then increase with the increasing of the doping C.Possion ratio of Mg(B1-xCx)2 is far less than 1/3 and the value of BH/GH is less than the material brittle-to-ductile transition critical criterion of 1.75 both of then indicate that Mg(B1-xCx)2 is a brittle compounds.更多还原