Mg_(17)Al_(12)相Ca合金化结构稳定性的第一原理研究

First-principle study on structural stability of Ca alloying Mg_(17)Al_(12) phase

采用第一原理赝势平面波方法,计算了Mg17Al12相Ca合金化前后的能态与电子结构。计算结果显示:当Ca分别置换Mg17Al12相中Mg(Ⅰ)、Mg(Ⅱ)和Mg(Ⅲ)原子时,(Mg17-xCax)Al12相(x=0,1,4,12)的负生成热逐渐升高、结合能逐渐增大,表明Ca置换Mg17Al12相中Mg(Ⅲ)原子时其Ca合金化能力最强,合金化后形成的(Mg5Ca12)Al12相结构稳定性最高。电子态密度(DOS)分析结果表明:Ca合金化后Mg17Al12相结构稳定性升高的主要原因是由于合金化后来自Al(p)和Ca(s)的价电子使其在低能区的成键电子数增多。

Using the first-principle pseudopotential plane-wave method, the energy and electronic structures of Ca alloying Mg_(17)Al_(12) phase were investigated. The results show that the negative formation heat and the cohesive energy of (Mg_(17-x)Ca_x)Al_(12) (x=0, 1, 4, 12) phases gradually increase when the Mg atoms at Ⅰ, Ⅱ, Ⅲ positions of Mg_(17)Al_(12) phase are substituted by Ca respectively, which indicates that for the alloying ability of (Mg_(17-x)Ca_x)Al_(12)(x=0, 1, 4, 12) phase the replacement of Ca for Mg(Ⅲ) atoms is the strongest among the above three substitutions, and the ((Mg_5Ca_(12))Al_(12)) phase formed by this manner has the highest structural stability. After compared the densities of states (DOS) of (Mg_(17-x)Ca_x)Al_(12) phases, it is found that the increase of the structural stability of Mg_(17)Al_(12) 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.