Ab initio investigation of native point defects in Mg₂₄Y₅

Eight possible native point defects in Mg₂₄Y₅ are studied from the density functional theory (DFT) calculations within GGA approximation. The energetic results show that anti-site defects with lower formation energies are energetically favored over vacancies. Under both Mg-rich and Y-rich conditions, Mg_Y1 defect is dominant due to the lowest defect formation energy, followed by Y_Mg2, Mg_Y2 and Y_Mg1, which reasonably explains the Mg-rich off-stoichiometry of Mg₂₄Y₅ alloys. For vacancy defects, the formation energies on the two Mg sub-lattices are smaller than ones on two Y sub-lattices, and V_Mg1 has the lowest formation energy, while V_Y2 is most unlikely due to the highest formation energy originating from the large mismatch in atomic size and the strong interaction of Y with surrounding atoms. The defect concentration distribution as a function of temperature and stoichiometry is further obtained from grand canonical statistics. The size factor and electronic structure are further discussed, demonstrating that Mg₂₄Y₅ alloy is typical system in which the point defects are affected by strong size effect due to the large atomic size radius and strong electronic factor caused by the intensive interaction of Y with the surrounding atoms. - Highlights: • The most stable point defect in Mg₂₄Y₅ is anti-site defect Mg_Y1. • Vacancy is not likely to play an important role for the off-stoichiometry of Mg₂₄Y₅. • Defect formation energy depends strongly on chemical potential. • Size effect possesses significant influence on formation of point defects. • The total DOS reveal the electronic mechanism for the stability of anti-site defects.