Vacancy-Vacancy Interaction Induced Oxygen Diffusivity Enhancement in Undoped Nonstoichiometric Ceria

FL Yuan and YW Zhang and WJ Weber, JOURNAL OF PHYSICAL CHEMISTRY C, 119, 13153-13159 (2015).

DOI: 10.1021/acs.jpcc.5b01317

Molecular dynamics simulations and molecular static calculations have been used to systematically study oxygen vacancy transport in undoped nonstoichiometric ceria. A strong oxygen diffusivity enhancement appears in the vacancy concentration range of 2-4% over the temperature range from 1000 to 2000 K. An Arrhenius ion diffusion mechanism by vacancy hopping along the < 100 > direction is unambiguously identified, and an increasing trend of both the oxygen migration barrier and the prefactor with increasing vacancy concentration is observed. Within the framework of classical diffusion theory, a weak concentration dependence of the prefactor in oxygen vacancy migration is shown to be crucial for explaining the unusual fast oxygen ion migration in the low concentration range and consequently the appearance of a maximum in oxygen diffusivity. A representative ?100? direction interaction model is constructed to identify long-range vacancy-vacancy interaction as the structural origin of the positive correlation between oxygen migration barrier and vacancy concentration.

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