First-principles study of point defects in C14 MgZn2 Laves phase

• Defect formation energy depends sensitively on the environment conditions.
• Incorporation of lattice vibrations results in obvious temperature effect.
• The point defect of Mg-rich side in MgZn2 is double at low temperature.
• The anti-site defects are energetically favored over vacancies at high temperature.
• The present study completely explains the different experimental observations.

The density function theory calculations are performed to study the native point defect in MgZn2. The calculated defect formation energy depends largely on the atomic chemical potentials of Mg and Zn, and suggests that Mg anti-site on Zn2 site is dominant under strong Mg-rich condition, while Zn2 vacancy is favorable under moderate Mg-rich condition. For Zn-rich side Zn anti-site on Mg sublattice is energetic. Lattice vibration effect is further considered, it is found that incorporation vibration contribution into defect formation energy results in obvious temperature effect. The present results indicate that defect configuration is sensitive to the environment conditions, reasonably explain the different experimental observations. The derived point defect concentration undergoes a dramatic change from Zn- to Mg-rich near the stoichiometry. The locally atomic geometry around point defect and electronic structure are also studied, which further reveal the underlying mechanism for structure of point defect.