Nanocrystalline zinc ferrite is synthesized at room temperature by high-energy ball-milling the stiochiometric (1:1 mol%) mixture of ZnO-alpha-Fe2O3. Nucleation of nanocrystalline Zn-ferrite particle takes place by solid-state diffusion between nanocrystalline ZnO and alpha-Fe2O3 particles. Both the particle size and collision temperature favors the formation mechanism. The process of mechanosynthesis of zinc ferrite at room temperature led to the formation of metastable inverse spinel structure. The formation of normal and inverse spinel structures is noticed after 30 min and 2.5 h ball-milling, respectively, and the degree of inversion increased with increasing milling time. The structural and microstructural evolution of ZnFe2O4 caused by milling is investigated by X-ray powder diffraction. The relative phase abundances of different phases, particle size, rms strain, lattice parameter change, etc. have been estimated from Rietveld powder structure refinement analysis of XRD data. A significant amount (wt.%) of nanocrystalline ZnFe2O4 is formed within 2.5 h ball-milling with a very compressed lattice parameter. However, lattice parameter of 10 h-milled sample annealed at 1273 K for 1 h agreed well the literature value and surprisingly, inverse spinel structure is completely absent in the annealed material. This leads to the conclusion that inverse spinel structure is a metastable one, formed under high-energy impact with a very small particle size (similar to6 nm) and high temperature annealing even for a shorter time is sufficient to reduce the disorderness in occupancy of tetrahedral and octahedral sites by Zn2+ and Fe3+ cations. (C) 2003 Elsevier B.V. All rights reserved.