Hydrothermal techniques have been used to synthesize samples of ZnxFe3-O-x(4) (x = 0.0-1.0) starting with ZnSO4 center dot 7H(2)O/FeSO4 center dot 7H(2)O aqueous solution. The sequence of phases, structural and magnetic properties were followed by X-ray diffraction (XRD), Mossbauer spectroscopy and transmission electron microscopy (TEM). Refinement of the XRD spectra yielded the dependence of the lattice parameters of zinc-doped magnetite and zinc ferrite phase as function of the Zn molar concentration x. As well, the particle diameter was derived and represented as a function of Zn content x. As a function of Zn concentration, the phase content of hydrothermally synthesized samples was found to consist of zinc-doped magnetite, goethite and zinc ferrite. Consistent with the XRD results, Mossbauer spectroscopy data indicate the presence of magnetite and goethite at x <= 0.2, magnetite and zinc ferrite at x <= 0.9 and pure zinc ferrite only at high zinc concentrations. The presence of different magnetite phases was confirmed by TEM and particles with a size of 50 nm were identified. Our results show that zinc ferrite is formed at high zinc concentration by the hydrothermal method and an acicular component of goethite-magnetite is obtained at low zinc content. (C) 2007 Elsevier B.V. All rights reserved.