Mechanistic understanding of vacancy formation energies in FCC concentrated alloys from DFT calculations

Due to chemical and lattice symmetries, pure metals have single values of properties such as vacancy formation energy ( E v f ). However, concentrated alloys, that consist of multiple elements in large proportions randomly distributed on a crystal lattice, have a range of E v f s due to diverse nearest neighbor (NN) environments. While previous studies have illustrated a correlation between NN chemistry and E v f , in this work, using density functional theory (DFT) calculations, we take a step forward and show that atomic volume and electronegativity also have a significant effect on the E v f . Specifically, we show that larger atomic volume increases E v f . In addition, charge gain due to higher electronegativity of a central atom also increases E v f s. We find that such mechanisms can lead to very large E v f variations, at times over 1 eV. The study is performed in model FCC alloys including binary Ni-Cu, Cu-Au, Ag-Au, and ternary Ni-Cu-Au. We show that the fundamental principles observed in binaries translate into ternaries. These observations would be helpful in the design and development of concentrated alloys for high temperature applications.