Synthesis and characterization of Zn1-xNixFe2O4 spinels prepared by a citrate precursor

Nanocrystalline single-phase samples of Zn1-xNixFe2O4 ferrites (0 < x < 1) have been obtained via a soft-chemistry method based on citrate-ethylene glycol precursors.. at a relatively low temperature (650 degrees C). The influence of the nickel and zinc contents as well as that of heat treatments were investigated by means of X-ray powder diffraction, Brunauer-Emmett-Teller (BET) surface area, scanning electron microscopy (SEM) and Fourier Transform Infrared (FTIR) Spectroscopy. Higher Ni content increases the surface areas, the largest one (similar to 20 m(2)/g) being obtained for NiFe2O4 annealed at 650 degrees C for 15 h. For all compositions, the surface area decreases for prolonged annealing at 650 degrees C and for higher annealing temperatures. Those results were correlated to the particle size evolution; the smallest particles (similar to 50 nm) observed in the NiFe2O4 sample (650 degrees C. 15 h) steadily increase as Ni ions were replaced by Zn, reaching similar to 100 nm in the ZnFe2O4 sample (650 degrees C 15 h). For all the Zn1-xNixFe2O4 samples and, whatever the heat treatments was, the FTIR spectra show two fundamental absorption bands in the range 650-400 cm(-1), characteristics of metal vibrations, without any superstructure stating for cation ordering. The highest v(1)-tetrahedral stretching. observed at similar to 615 cm(-1) in NiFe2O4, shifts towards lower values with increasing Zn, whereas the v(2)-octahedral vibration, observed at 408 cm(-1) in NiFe2O4 moves towards higher wavenumbers, reaching 453 cm(-1) in ZnFe2O4. (c) 2005 Elsevier Inc. All rights reserved.