Nanocrystalline yttria: Grain growth depression by thermal annealing in air

Nanocrystalline yttria was prepared by mechanical processing. A fraction was annealed in air at 473 K. Annealed and non-annealed powders were treated in Ar at temperatures between 700 and 1000 K, which induced a parabolic grain growth kinetics with an Arrhenius-like dependence on temperature. Grain growth is significantly slower in annealed powders with respect to non-annealed ones. This is related to oxygen chemical absorption during annealing in air and the consequent decrease of oxygen vacancies originally present in powders.