The ultrafine ZnFe2O4, MnFe2O4, and cation deficit Zn-Mn ferrites were obtained by thermal decomposition of appropriate mixed complex compounds with acetylacetone (2,4-pentadione) ligands ([M(AA),]) at 500 degreesC. In ZnFe2O4 cation distribution is partially inverse with 14% of Zn2+ ions at octahedral 16d sites, while MnFe2O4 is a normal spinel. Cation distribution in nonstoichiometric (Zn,Mn,Fe)(3-delta)O-4 (delta = 0.18-0.30) is found to be (Zn(x)Mn(y)square(epsilon))(8a)[Fe(z)square(v)](16d), with a random distribution of vacancies. Nonstoichiometry in Zn-Mn ferrites is accompanied by a cation valence change, i.e., partial oxidation of Mn2+ to Mn4+. Microstructure size-strain analysis shows isotropic X-ray line broadening due to the crystallite size effect and anisotropic X-ray line broadening due to the crystallite strain effect. In binary ferrites anisotropic X-ray line broadening due to the strain effect is higher in ZnFe2O4 than in MnFe2O4, while in ternary cation-deficient Zn-Mn ferrites it decreases as the vacancy concentration delta increases.