First-principles Studies Of Ni-Al And Ca-X(X=Si, Ge, Sn, Pb, Zn) Intermetallic Compounds

The structural properties, heat of formations, elastic properties, and electronic structures of Ni-Al and Ca-X(X=Si,Ge,Sn,Pb,Zn) intermetallic compounds were analyzed in detail by using density functional theory.For Ni-Al intermetallic compounds, higher calculated absolute values of heats of formation indicate a very strong chemical interaction between Al and Ni. According to the computational single crystal elastic constants, all the Al-Ni intermetallic compounds considered are mechanically stable. The polycrystalline elastic modulus and Poisson's ratio were deduced by using Voigt, Reuss, and Hill (VRH) approximations, and the calculated ratio of shear modulus to bulk modulus indicated that AlNi, Al₃Ni, AlNi₃ and Al₃Ni₅ compounds are ductile materials, but Al₄Ni₃ and Al₃Ni₂ are brittle materials. With increasing Ni concentration, the bulk modulus of Al-Ni intermetallic compounds increases in a linear manner. The electronic energy band structures confirm that all Al-Ni intermetallic compounds are conductors.We also study the properties of Ca-X(X=Si,Ge,Sn,Pb,Zn) intermetallic compounds. According to the computational single crystal elastic constants, except Ca₃₆Sn₂₃, CaZn₃, all the other Ca-X intermetallic compounds considered are mechanically stable. The results of polycrystalline elastic properties indicate that Ca₂Sn, Ca₇Sn₆, CaSn₃, Ca₂Pb, CaPb₃, Ca₃Zn, Ca₅Zn₃, CaZn, CaZn₁₁ are ductile materials, and the others are brittle materials. Higher calculated absolute values of heats of formation indicate a very strong chemical interaction between Ca and Si, Ge, Sn, Pb due to the research of the heat of formation. But the heats of formation for Ca-Zn intermetallic compounds are obviously smaller than Ca-X (X=Si,Ge,Sn,Pb). Finally the electronic energy band structures are studied. According to the result, Ca₂Si, Ca₂Ge, Ca₂Sn, Ca₂Pb are direct-gap semiconductor. And their band gaps are 0.324eV, 0.265eV, 0.06eV and 0.07eV, respectively. Ca₃Si₄ is indirect band gap semiconductor and its band gap is 0.598eV. All the other compounds are conductors.