Structural evolution of ball-milled ZnFe2O4

Nanostructured zinc ferrite produced by milling in both low-energy and high-energy ball mills has been investigated by X-ray diffraction and Mossbauer effect spectroscopy. The lattice parameter of the milled products remains essentially unchanged from that of equilibrium ZnFe2O4 with the steady-state average particle size found to decrease to d=18(2) nm on low energy milling compared with d=8(1) nm on high energy milling. The room temperature Mossbauer spectra of the milled materials have been analysed using two doublets, one of which is considered to be associated primarily with the octahedral lattice sites. Spectral broadening is observed with decreasing particle size, particularly below d-10 nm, for which the effects of magnetic hyperfine splitting become evident. The mean inversion parameter of nanostructured ZnFe2O4 is found to increase to csimilar to0.75 for particle sizes of dsimilar to8 nm reflecting the systematic evolution of zinc ferrite from its normal spinel structure towards an inverse spinel structure on mechanical treatment as observed previously. The other factors which contribute to the Mossbauer spectra of nanostructured ZnFe2O4 (dsimilar to8-70 nm) are discussed. (C) 2002 Elsevier Science B.V. All rights reserved.