Direct diffusion through interpenetrating networks: Oxygen in titanium
  How impurity atoms move through a crystal is a fundamental and recurrent question in materials. The previous understanding of oxygen diffusion in titanium relied on interstitial lattice sites that were recently found to be unstable, making the diffusion pathways for oxygen unknown. Using first-principles quantum-mechanical methods, we find three oxygen interstitial sites in titanium, and quantify the multiple interpenetrating networks for oxygen diffusion. Surprisingly, no single transition dominates, but all contribute to diffusion. 
Henry H. Wu, Dallas R. Trinkle (Department of Materials Science and   Engineering, University of Illinois, Urbana-Champaign)
cond-mat.mtrl-sci