Magnetism and Recoilless Fraction of Cerium-Doped Hematite Nanoparticles System
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Magnetism and Recoilless Fraction of Cerium-Doped Hematite Nanoparticles System Monica Sorescu1, and Lucian Diamandescu2 1 Physics, Duquesne University, 600 Forbes Avenue, Pittsburgh, PA, 15282 2 Materials Science, National Institute for Materials Physics, Bucharest, 77125, Romania ABSTRACT 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) and Mössbauer spectroscopy. 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 hours of milling, followed by a further decrease of the f factor due to the appearance of nanoparticles in the system. INTRODUCTION The study of semiconducting oxides has become increasingly important due to their sensing properties in the detection of toxic and dangerous gases, such as CO, NO2, Cl2 and CH4 [1-3]. Enhanced gas properties are expected for nanostructured semiconducting oxides due to the great surface activity provided by their high surface areas [4-10]. However, the mechanism of sensing in xCeO2-(1-x)α-Fe2O3 is not well understood, due to incomplete understanding of its microstructure characteristics. In this paper we report the mechanochemical synthesis of xCeO2-(1-x)α-Fe2O3 nanoparticles for x=0.1 and 0.5. X-ray diffraction (XRD) and Mössbauer spectroscopy have been used to correlate the structure, morphology and phase dynamics in connection with the cerium concentration. Experimental evidence for compositional transition in this system is given by precise measurements of the recoilless fraction. EXPERIMENTAL Powders of hematite and cerium dioxide were milled at different molar concentrations (x=0.1 and 0.5) in a hardened steel vial with twelve stainless steel balls (type 440; eight of 0.25 in diameter and four of 0.5 in diameter) in the SPEX 8000 mixer mill for time periods ranging from 2 to 16 hours. The ball/powder mass ratio was 1:5 and all experiments were performed in a glove box under protective argon atmosphere. The structure of the powders was examined using Rigaku D-2013 X-ray diffractometer with CuKα radiation (λ=1.540598 Å). The 57Fe Mössbauer spectra were recorded at room temperature using a 57Co in Rh source and an MS-1200 constant acceleration spectrometer.
RESULTS AND DISCUSSION Figures 1 (a)-(e) and 2 (a)-(e) represent the XRD patterns of ceria-do
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