Vacancy-induced brittle to ductile transition of W-M co-doped Al(3)Ti (M=Si, Ge, Sn and Pb)

We investigated the effect of vacancy formation on brittle (D0(22)) to ductile (L1(2)-like) transition in Al(3)Ti using DFT calculations. The well-known pseudogap on the density of states of Al(3)Ti migrates towards its Fermi level from far above, via a W − M co-doping strategy, where M is Si, Ge, Sn or Pb respectively. In particular, by a W − M co-doping the underline electronic structure of the pseudogap approaches an octahedral (L1(2): t(2g), e(g)) from the tetragonal (D0(22): e(g), b(2g), a(1g), b(1g)) crystal field. Our calculations demonstrated that (1) a W-doping is responsible for the close up of the energy gap between a(1g) and b(1g) so that they tend to merge into an e(g) symmetry, and (2) all M-doping lead to a narrower gap between e(g) and b(2g) (moving towards a t(2g) symmetry). Thus, a brittle to ductile transition in Al(3)Ti is possible by adopting this W − M co-doping strategy. We further recommend the use of W-Pb co-doped Al(3)Ti to replace the less anodic Al electrode in Al-battery, due to its improved ductility and high Al diffusivity. Finally this study opens a new field in physics to tailor mechanical properties by manipulating electron energy level(s) towards higher symmetry via vacancy optimization.