Influence of H, C, N and O impurities on the stability of Mg and Al from first-principles calculations

Abstract

The influence of H, C, N and O impurities on the energetic and mechanical stabilities of Mg and Al were studied by first-principles total energy calculations. The occupation preference and formation energy of impurities in Mg and Al were estimated. H and C decrease the energetic stability of Mg and Al, while N and O significantly increase it. In Mg, H and O prefer to occupy the tetrahedral site, while C and N tend to occupy the octahedral site. In Al, only C prefers the octahedral site, while other elements will occupy the tetrahedral site. Electronic structures were analyzed to clarify the bonding properties and stability mechanisms of H, C, N and O in Mg and Al. The bonding characteristics around the Fermi energy level respond to the influence of impurities on the stability of Mg and Al. This work shows that all the impurities form strong bonds with the host atoms, but H and C weaken the interactions between host atoms, while N and O rarely affect these kinds of interactions. It seems that these bonding characteristics are independent of the crystal structures of matrices and the valence electron configurations of the host atoms. Elastic constants of impurity-containing systems were estimated from curves of energy against strain to evaluate the mechanical stability and elastic properties of the systems considered. All the impurity-containing systems satisfy the mechanical stability criteria. The influence of impurities on the elastic properties of Mg and Al was also studied.