Characterization of the Lattice Transitions and Impurities in Manganese and Zinc Doped Ferrite Nanoparticles by Raman Spectroscopy and X-ray Diffraction (XRD)

Temperature-induced phase transitions and the presence of impurities to the spinel phase ferrite nanoparticles were comparatively assessed using the same annealed samples, by Raman spectroscopy (RS) and X-Ray Diffraction (XRD), in order to point out advantages and disadvantages of either method depending on the research issue at hand. RS revealed gradual phase transitions from predominantly magnetite-like below 250 degrees C with the possibility of tracking cation vacancies, over maghemite-like at 300-600 degrees C, hematite-dominated in the 700-1000 degrees C range, and back to a spinel phase at 1100 degrees C with a different arrangement of cations on A-sites than the starting sample. On the other hand, XRD on the same samples showed abrupt transition from the spinel structure to hematite between 600 and 700 degrees C, and back to spinel at 1100 degrees C, but this technique performed better at revealing other oxide phases present below the identification threshold of Raman spectroscopy. Magnetization measurements support the phase transitions assignments, showing no saturation magnetization for the samples annealed at 700-900 degrees C, while those annealed at 1000 and 1100 degrees C re-gained saturation magnetization up to 31.7 emu/g. Magnetite- and maghemite-like structures in the 100-300 degrees C range are more clearly distinguished by RS than XRD, due to their isostructural character (both have face-centered cubic symmetry). These analytical aspects have to be understood in order to achieve more efficient and comprehensive characterization of synthesized ferrite nanoparticles.