8 nm Co nanoparticles with various crystalline structures called polymorphs were produced using different synthetic procedures, such as using reverse micelles, the thermal decomposition of organometallics approach or the hot injection process. These 8 nm Co nanoparticles differing by their crystalline structures are exposed to oxygen at elevated temperature. The fcc Co polycrystalline nanoparticles produce either Co–CoO yolk–shell or CoO hollow structures whereas amorphous Co nanoparticles produce Co–CoO core–shell nanoparticles. Furthermore, single domains with either hcp or e crystalline structure behave differently upon oxygen diffusion. Co–CoO nanoparticles were produced from the hcp phase while CoO hollow nanoparticles were the product for e-phase Co nanocrystals.
Source : Crystal polymorphism: dependence of oxygen diffusion through 2D ordered Co nanocrystals. Z .Yang, J.Yang, J.Bergström, K.Khazen, and M. P. Pileni Phys. Chem. Chem. Phys., 2014,16, 9791-9796.