Structure and characterization of cerium-doped hematite nanoparticles

Cerium-doped hematite particles of the type xCeO2-(1−x)α-Fe2O3 (x=0.1, 0.5) were synthesized using mechanochemical activation and characterized by X-ray diffraction (XRD), Mössbauer spectroscopy and transmission electron microscopy (TEM). XRD patterns yielded the dependence of lattice parameters and particle size as a function of ball milling time for each value of the molar concentration x. For x=0.1, the Mössbauer spectra were fitted with one or alternatively, two sextets, corresponding to Ce ions substituting Fe ions in the hematite structure. For x=0.5, Mössbauer spectra fitting required the addition of a quadrupole-split doublet, representing Fe substituting Ce in the CeO2 lattice. We evidenced this transition using our recently developed method for precise determination of the recoilless fraction in a single room-temperature transmission Mössbauer measurement of a two-absorber sample. We observed the occurrence of a minimum in the values of the recoilless fraction for t=4 h of milling, followed by a further decrease of the f factor due to the appearance of nanoparticles in the system. This system was also obtained by magnetomechanical activation in an applied magnetic field of 0.4 T. It was concluded that magnetic ball milling is a useful technique for obtaining magnetic systems with dilute impurities. TEM and high-resolution TEM were performed on the milled samples to examine the morphology of the nanoparticles obtained.