Failure of the Hume-Rothery stabilization mechanism in theAg5Li8 gamma-brass studied by first-principles FLAPW electronic structure calculations

Abstract

The first-principles FLAPW (full potential linearized augmentedplane wave) electronic structure calculations were performed for theAg5Li8 gamma-brass, which contains 52 atoms in a unit cell and has been known for many years asone of the most structurally complex alloy phases. The calculations were also made for itsneighboring phase AgLi B2 compound. The main objective in the present work is to examine if theAg5Li8 gamma-brass is stabilized at the particular electrons per atom ratioe/a = 21/13 in the same way as some other gamma-brasses likeCu5Zn8 and Cu9Al4, obeying the Hume-Rothery electron concentration rule. For this purpose, thee/a valuefor the Ag5Li8 gamma-brass as well as the AgLi B2 compound was first determined by means of the FLAPW-Fouriermethod we have developed. It proved that both the gamma-brass and the B2 compound possess ane/a value equal tounity instead of 21/13. Moreover, we could demonstrate why the Hume-Rothery stabilization mechanism fails for theAg5Li8 gamma-brass and proposed a new stability mechanism, in which the unique gamma-brassstructure can effectively lower the band-structure energy by forming heavily populatedbonding states near the bottom of the Ag-4d band.