First-principle study on structural stability of Ca alloying Mg₁₇Al₁₂ phase

Using the first-principle pseudopotential plane-wave method, the energy and electronic structures of Ca alloying Mg₁₇Al₁₂ phase were investigated. The results show that the negative formation heat and the cohesive energy of (Mg_17-xCa_x)Al₁₂ (x = 0, 1, 4, 12) phases gradually increase when the Mg atoms at I, II, III positions of Mg₁₇Al₁₂ phase are substituted by Ca respectively, which indicates that for the alloying ability of (Mg_17-xCa_x)Al₁₂ (x = 0, 1, 4, 12) phase the replacement of Ca for Mg(III) atoms is the strongest among the above three substitutions, and the (Mg₅Ca₁₂)Al₁₂ phase formed by this manner has the highest structural stability. After compared the densities of states (DOS) of (Mg_17-xCa_x) Al₁₂ phases, it is found that the increase of the structural stability of Mg₁₇Al₁₂ phase alloyed by Ca attributes to an increase in the bonding electron numbers at lower energy level below Feimi level, which mainly originates from the contribution of valence electron numbers of Al(p) and Ca(s) orbitals.