We have studied the cation distribution over the tetrahedral and octahedral sites in the spinel structure of nanocrystalline NiZnFeO ferrites prepared by spray pyrolysis. Fe Mössbauer spectroscopy data for the ferrites demonstrate that, depending on the composition of the materials, the tetrahedral site may accommodate only Fe (inverse spinel, x ≥ 0.4) or both Fe and Zn cations (mixed spinel, x = 0 and 0.2), which accounts for the fact that the composition dependence of the unit-cell parameter for the ferrites deviates from Vegard's law. [ABSTRACT FROM AUTHOR]