First-principles study of the structure of Mg/Nb multilayers

The magnesium (Mg) phase characterized within Mg/Nb multilayers can adopt either a body-centered cubic (bcc-Mg) or hexagonal close packed (hcp-Mg) structure, depending on the Mg layer thickness. Using first-principles density functional theory, we find that bcc-Mg has a similar weight density of hcp-Mg, lower Young's modulus, and higher shear modulus than hcp-Mg, and the same conventional slip systems as the bcc structure. A simple theoretical model is developed to predict the structural stability of both the bcc-Mg/Nb and hcp-Mg/Nb multilayers. It shows that the bcc-Mg/Nb multilayer is energetically favorable when the bcc-Mg layer is less than 4.2 nm. (C) 2014 AIP Publishing LLC.