Nanoparticles of cobalt ferrite prepared by the co-precipitation method with crystallite size varying from 4.7 to 41nm were characterized by positron annihilation lifetime spectroscopy. Three lifetime components were fitted to the lifetime data. The shortest lifetime component was attributed to the delocalized positron lifetime shortened by defect trapping. The intermediate lifetime was attributed to the positron annihilation in diffuse vacancy clusters or micro-voids at the grain boundaries and at the grain-boundary triple points. The longest component corresponded to the pick-off annihilation of ortho-positronium formed at the larger voids. The variations in these lifetimes and their relative intensities with annealing temperature and crystallite size were studied in detail.

Investigation of Nanocrystalline CoFe2O4 by Positron Annihilation Lifetime Spectroscopy. S.Bandyopadhyay, A.Roy, D.Das, S.S.Ghugre, J.Ghose: Philosophical Magazine, 2003, 83[6], 765-73