The native point defects in C14 Mg2Ca Laves phase: A first-principles study

The native point defects in C14 Mg₂Ca Laves phase are studied from the first-principles density functional theory calculations within GGA approximation. The defect formation energies indicate that anti-site defects are energetically favored over vacancies. Under Mg-rich and even general Ca-rich condition, defect Mg_Ca of Mg anti-site on Ca sublattice is favorable owing to the lowest formation energy. The Ca_Mg2 defect of Ca anti-site on Mg2 sublattice is also likely dominant only under extreme Ca-rich environment. The present results could explain reasonably the asymmetric off-stoichiometry of Mg₂Ca. The effective point defect concentrations of Mg₂Ca as a function of composition and temperature at experimental range are also calculated from a canonical statistical model, and the derived results show a linear relationship between the logarithm of defect concentration and T^?1. Geometrical factor is further studied, and it is found that atomic size possesses an obvious influence on the structure of point defect in Mg₂Ca. The electronic feature is further studied to reveal underlying mechanism for formation of point defects.