A molecular dynamics simulation of energetics and diffusion of point defects in a Au–Ag alloy

Abstract

For revealing an aging mechanism for self-irradiation in a Pu–Ga alloy, we carried out a molecular dynamics (MD) simulation on a substitutional material, i.e., Au–Ag alloy. In this work, we estimate physical and microscopic properties of the Au–Ag alloy containing various point defects using a MD method, in particular, formation energy for point defects, migration energy for point defects diffusion into interstitial sites, and diffusion coefficient for the Au–Ag alloy containing point defects, such as vacancy, He atom and He-vacancy (He-V) cluster. The results indicate that volumetric heat capacity and linear expansion coefficient would decrease due to the various point defects, and He atom has the most remarkable influence on the physical properties of the Au–Ag alloy for point defects considered in this work. The formation energy of Au and Ag self-interstitial atom indicates that Octa1 is the most stable site, and structural stability of octahedral (Octa) interstitial sites for the He atom obeys \(\hbox {Octa1}> \hbox {Octa2}> \hbox {Octa4} > \hbox {Octa3}\). For the \(\hbox {He}_{n}\hbox {V}_{m}\) cluster, the formation energy of the defect structure is most stable at \(n = m\). The diffusion coefficient of the He-V cluster is relatively smaller, showing that vacancy defects would further decrease atomic diffusion. An influence of various point defects on the diffusion velocity in the Au–Ag alloy obeys the He-V \(\hbox {cluster}> \hbox {He}> \hbox {vacancy}> \hbox {Ag} > \hbox {Au}\).