First-principles Investigation Of Point Defect And Atomic Diffusion In Al₂Ca

Atomic diffusion is one of important fundamental processes for formation of Mg alloy materials,and has been attracting widespread attention.Especially,relevant diffusion data in critical precipitated phase Al2Ca has been rarely reported so far to our best knowledge.Thus,it is necessary and valuable to investigate atomic diffusion in Al2Ca.Considering the difficulty and precision of experimental measurement,theoretical research is an important means to understand the diffusion process in crystal materials.The first-principles calculation based on density functional theory(DFT)is a particularly effective theoretical method,and has been widely used in the prediction of performance of solid materials and made great progress,so in this paper atomic diffusion in Al2Ca has been studied from first-principles calculations.The structure and relative stability of the native point defects are studied at first because these point defects often play an important medium role in atomic diffusion.The formation energies of point defects are calculated and the relative stability of point defects is discussed.The calculated results show that the dominating defects structure are AlCa and CaAi antisite defects on Al-rich and Ca-rich side of off-stoichiometry,respectively.The formation of vacancies in the two sublattices is more difficult than that of the antisite point defects.The formation energies of the composite defects associated with the diffusion studies and the corresponding atomic diffusion migration energy barriers are further calculated.Then several predominant diffusion processes in Al2Ca are studied,including sublattice one-step mechanism,3-jump vacancy cycles and antistructure sublattice mechanism.The associated energy profiles are calculated with climbing image nudged elastic band(CI-NEB)method,then the saddle points during atomic diffusion and activation barriers are further determined.The resulted activation barriers show that both A1 and Ca can diffuse mainly mediated by neighbor vacancy on their own sublattice.3-jump cycle mechanism mediated by Vca may make some contribution to the overall Al diffusion.And antistructure(AS)sublattice mechanism can also play an important role in Ca atomic diffusion owing to the moderate activation barrier.