Anomalous Energy Pathway of Vacancy Migration and Self-Diffusion in Hcp Ti
S L Shang, L G Hector Jr., Y Wang, and Z K Liu
Phys. Rev. B 83, 224104 (2011)
An anomalous energy pathway with energetically equivalent double saddle points for vacancy mediated self-diffusion within an hcp-Ti basal plane is unveiled by density functional theory. Examination of migration pathway and phonon force constants suggests that the migrating atom tries to follow the bcc-hcp phase transition via the Burgers shear deformation. We propose that the formed energy local minimum with a bcc-like atomic environment between the two saddle points originates from the existence of high-temperature bcc phase and is a feature of Group IV hcp metals with bcc-hcp phase transition. Computed diffusion coefficients are in favorable accord with experiments for hcp Ti.