Nano-sized crystalline gamma-Fe2O3 (particle size ca. 7 nm) was synthesized by mild oxidation of iron micelle obtained from Fe(CO)(5). Heat treatment at 400 degrees C in vacuum was effective to remove a large amount of organic impurities, the weight of which was over 40 wt.% in the as-prepared solid phase. Significant suppression of the spinel-rocksalt transformation was confirmed as the major nano-sized effect and led to the reversible topochemical lithium interaction with the corresponding lattice volume expansion. (c) 2005 Elsevier B.V. All rights reserved.