First-principles Calculation of Stability and Mechanical Properties of Ca-doped Mg₁₇Al₁₂

The cell structures of four compounds (Ca_xMg_17-x)Al₁₂（x=0,1,4,12） formed by doping Ca into Mg₁₇Al₁₂were optimized by first principles of density functional theory.The structural stability,electronic properties and mechanical properties of the four compounds were calculated.The results show that the heat of formation and binding energy of the four compounds are all negative.Among them,the structure of (Ca₁₂Mg₅)Al₁₂compound is the most stable and the alloying ability is best,because the densities of states result show that the valence electron hybridization of Ca （s）,（p） and Al （s）,（p） orbitals is strong.The results of charge density and population indicate that there are metal bonds,covalent bonds and ionic bonds in(Ca_xMg_17-x)Al₁₂（x=0,1,4,12） compounds.Compared with other compounds,ionic bonds in (Mg₅Ca₁₂)Al₁₂are stronger.The calculation results of elastic constants and moduli show that (Ca_xMg_17-x)Al₁₂（x=0,1,4,12） compounds are at brittle phase,and(Mg₁₃Ca₄)Al₁₂compound owns the least brittleness and best ductility.