First-Principles Investigation of Titanium Nanoparticle Oxidation

We perform first-principles calculations to investigate the initial stages of titanium nanoparticle oxidation. We determine the most stable structure of a 181-atom decahedral nanoparticle with various oxygen coverages ranging from a single atom to full oxidation of the surface. Linear Oad−Ti−Oad bonding configurations on the nanoparticle surface are found to be most stable for low oxygen coverage. The degree of lattice expansion is observed to gradually increase with increasing oxygen content up to 8.2% for full oxidation of the surface. To investigate likely mechanisms for subsequent subsurface oxidation, we calculate energy barriers for many inequivalent oxygen diffusion pathways. We find that the most favorable pathways involve penetration of oxygen into subsurface octahedral sites in the center of facets where the strain is largest. The results provide atomistic insight into the oxidation behavior of Ti nanoparticles and highlight the important role played by adsorption induced strain.