Influences of alloying elements and oxygen on the stability and elastic properties of Mg17Al12

Influence of alloying elements (Ca, Mn, Ni, Cu, Zn, Zr, Sn, and La) and oxygen on stability and elastic properties of Mg17Al12 has been studied by first principles total energy calculations. The occupation preferences of oxygen and alloying elements in Mg17Al12 are identified. Ca, Zr, and La tend to substitute for Mg atoms, Zn, Cu, and Ni prefer to occupy Al site, and Mn and Sn show positive occupation energy for substituting both Mg and Al atoms. The impurity oxygen prefers to occupy interstitial sites surrounded by four Mg atoms regardless the presence of alloying elements in this system. Elastic constants were estimated to evaluate the mechanical stability of alloyed systems. The results show that alloys which own negative occupation energy also satisfy the mechanical stability criteria. Electronic structures were analyzed to clarify the intrinsic mechanisms of how alloying elements and oxygen influence the stability of Mg17Al12. The stabilization effect of alloying elements and oxygen was found to originate from the strong bonding interaction with the matrix.