Designing Mixed Oxides Magnetic Nanoparticles for Sensing Applications
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Designing Mixed Oxides Magnetic Nanoparticles for Sensing Applications Monica Sorescu1 , L. Diamandescu1,2 , A. Tomescu2 and S. Krupa1 1 Duquesne University, Department of Physics, Pittsburgh, PA, U.S.A 2 National Institute for Materials Physics, Bucharest, Romania ABSTRACT Zirconium-doped hematite particles of the type xZrO2-(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. The Mössbauer spectra were fitted with one or alternatively, four sextets, corresponding to Zr ions substituting Fe ions in the hematite structure and further required the addition of a quadrupolesplit doublet, representing Fe substituting Zr in the ZrO2 lattice. We further correlated the structural properties of the zirconium-doped hematite system with the sensing properties. These were measured as function of temperature, gas concentration (carbon monoxide and methane) and variable humidity of air. The material system was found to be sensitive over the entire range of CO concentrations and the linearity of the sensor signal was not affected by the relative humidity of air, which makes it the ideal system for sensing devices. Comparative results obtained for tin-doped hematite nanoparticles are also presented. INTRODUCTION Investigations of semiconducting oxides have become increasingly important due to their sensing properties in the detection of toxic gases, such as carbon monoxide or methane [1-3]. Metal oxides are semiconductor materials best suited for gas sensing. In contradistinction to other semiconductors, which suffer irreversible chemical transformations at the surface and progressive oxidation due to prolonged and repeated heating in air, metal oxides absorb the oxygen on their surface reversible. If the semiconducting oxides are in addition nanostructured, it is expected that they will exhibit great surface activity due to their enhanced surface areas [414]. The mechanism of sensing in doped hematite nanoparticles is not well understood, however, due to incomplete understanding of their microstructure characteristics. In this paper we report the mechanochemical synthesis of xZrO2-(1-x)α-Fe2O3 nanoparticles for x=0.1 and 0.5 and the hydrothermal synthesis of xSnO2-(1-x)α-Fe2O3 over the entire composition range for x=0-1. X-ray diffraction (XRD) and Mössbauer spectroscopy have been used to analyze the structural and magnetic properties of doped hematite nanoparticles. We further correlate the structural properties of the material with measurements of the sensing properties of the system, in different gases, at different temperature and variable air humidity and observe that the zirconium-doped hematite nanoparticle system is an excellent material from the viewpoint of sensor device applications. EXPERIMENTAL Powders of hematite and zirconium dioxide were milled at diffe
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