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Spectroscopic Studies of M??ssbauer, Infrared, and Laser-Induced Luminescence for Classifying Rare-Earth Minerals Enriched in Iron-Rich Deposits
摘要： Rare-earth (RE) phosphates often appear as an accessory phase in igneous or metamorphic rocks; however, these rocks are composed of myriad chemical elements and nuclides that interfere with the qualitative or quantitative analyses of the RE phosphates over a range of concentrations in the absence of a pretreatment. In addition, the limit of each analytical methodology constrains the approach as well as the usefulness of the results in geoscience applications. Here, we report the specific mineral characterization of RE-containing ores from Yen Phu mine, Vietnam, using a range of state-of-the-art spectroscopic techniques in conjunction with microscopy: M?ssbauer spectroscopy, infrared microspectroscopy, time-resolved laser-induced fluorescence spectroscopy (TRLFS), and scanning electron microscopy with energy-dispersive X-ray spectroscopy. Because the distribution of each element in the deposit differs, such combinatorial works are necessary and could lead to more plausible answers to questions surrounding the point of origin of RE elements. The results of our M?ssbauer spectroscopic analysis indicate that the three ores sampled at different locations all contain magnetite-like, hematite-like, and iron(III) salts other than hematite. In addition, we confirmed the presence of phosphate around the grain boundary in the magnetite-like mineral phase by infrared microspectroscopic analysis. The present analytical findings of trace amounts of europium(III) using TRLFS suggest that the europium ions generate identical luminescence spectra despite being embedded in three different matrices of iron minerals. This demonstration highlights the benefits of combinatorial spectroscopic analyses to gain insights into the effects of the environment of REs on their solid-state chemistry and shows the potential utility of TRLFS as a resource mining tool. Further applications of this approach in the analytical screening of rocks and minerals are feasible.
关键词： energy-dispersive X-ray spectroscopy,spectroscopic techniques,rare-earth phosphates,Yen Phu mine,infrared microspectroscopy,scanning electron microscopy,time-resolved laser-induced fluorescence spectroscopy,M?ssbauer spectroscopy,Vietnam
更新于2025-09-23 15:21:01
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57Fe M?ssbauer and XRD studies on β-FeSi2 prepared by high energy mechanical attrition
摘要： The evolution of different phases of Fe-Si binary system on milling elemental Fe and Si has been carried out in argon atmosphere at 1000 rpm using the hardened tungsten carbide powders has been studied by x-ray diffractometry and 57Fe M?ssbauer spectroscopy. The milling medium. The sizes of both Fe and Si are found to be less than 50 nm on milling the mixture for 50 min. Metallic α-FeSi2 formation takes place at this stage due to enhanced reactivity caused by reduction in particle size. The semiconducting β-FeSi2 phase along with ε-FeSi and a metastable Fe-Si solid solution are found to be formed on annealing the milled product at 500 °C. A clean semiconducting β-FeSi2 phase forms on milling Fe and Si for 50 minute followed by annealing at 800 °C for 2 hrs.
关键词： M?ssbauer spectroscopy,X-ray diffraction,semiconducting β-FeSi2
更新于2025-09-23 15:21:01
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Bulk and surface characterisation of micrometer-thick cobalt ferrite films grown by IR PLD
摘要： We have studied micrometer-thick cobalt ferrite films deposited on Si (100) single crystal substrates by nanosecond pulsed laser deposition at 1064 nm.The thickness of the deposited films (1.3 μm) was monitored by AFM. The chemical and structural characterisation of the films was carried out by Raman spectroscopy and transmission M?ssbauer spectroscopy at 300 and 26 K. For comparison purposes, transmission M?ssbauer data at these two temperatures were also recorded from a commercial cobalt ferrite powder and the home-made target used to grow the films. The surface characterisation was performed by X-Ray Photoelectron Spectroscopy (XPS) and Integral Low Energy Electron Spectroscopy (ILEEMS). XPS showed Co and Fe to be present as Co2+ and Fe3+, as expected for cobalt ferrite. The Raman spectra showed the lines characteristic of cobalt ferrite. The M?ssbauer spectra, both in the transmission and backscattering modes, were fitted to two sextets whose hyperfine parameters are in good agreement with those expected from Fe3+ cations occupying the tetrahedral and octahedral sites in the spinel-related structure. No significant differences were observed in the relative areas of the two sextets in the transmission and ILEEMS spectra, suggesting that the cation distribution at the surface and the bulk are not too different. However, the relative areas of the two components changed drastically with temperature both in the spectra of the films as in those recorded from the cobalt ferrite standards. We discuss the possible origin of the evolution with temperature of those relative areas.
关键词： X-ray photoelectron spectroscopy,Raman spectroscopy,Cobalt ferrite,M?ssbauer spectroscopy,Pulsed laser deposition
更新于2025-09-10 09:29:36
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Structure, Magnetic and Photochemical Properties of Fe–TiO2 Nanoparticles Stabilized in Al2O3 Matrix
摘要： Fe–TiO2 nanoparticles with Fe concentration from 0.24 to 5 wt % were synthesized in a Al2O3 matrix through multiple impregnations from organic solutions of Ti n-butoxide and Fe acetylacetonate. Microstructure, morphology and magnetic properties of the composites were studied using X-ray analysis, transmission electron microscopy, energy-dispersive analysis, M?ssbauer spectroscopy and magnetic susceptibility. It was shown that the deposition of the solution with low concentration of Ti n-butoxide leads to the formation of mostly extensive Fe–TiO2 films with a small fraction of individual Fe–TiO2 nanoparticles. On the contrary, the increase of Ti n-butoxide concentration results in the formation of a great number of individual Fe–TiO2 nanoparticles on Al2O3. The size of these particles increases from 2–3 nm to 5–8 nm with the increase of Fe content in the samples from 0.24 to 1.0 (wt %). M?ssbauer spectroscopy revealed two types of magnetic ions. The first type of paramagnetic Fe3+ demonstrate spin–lattice relaxation properties while another one substitutes Ti4+ in the TiO2 structure thus forming Fe–TiO2 stabilized particles in the matrix. According to the magnetic data antiferromagnetic and ferromagnetic types of exchange spin coupling occur in Fe–TiO2/Al2O3 composites. The increase of Fe concentration in the composites from 1 to 5 wt % results in the narrowing of the TiO2 band gap from 3.2 to 2.7 eV and shifting the absorption edge in visual spectrum from 350–400 to 450–500 nm.
关键词： M?ssbauer spectroscopy,magnetic properties,Fe-doped TiO2
更新于2025-09-10 09:29:36
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Synthesis, crystal structure, M?ssbauer spectroscopy, optical and magnetic properties of Cs2M2Fe(PO4)3 (M = Mn, Co, Ni, Cu) ordered pollucite structure
摘要： Four isomorphous iron phosphates Cs2M2Fe(PO4)3 (M = Mn, Co, Ni, Cu) have been synthesized as powder by conventional solid state technic and characterized by X-ray diffraction, magnetic susceptibility, diffuse reflectance and M?ssbauer spectroscopies. All these compounds crystallize in the space group I4132 of the cubic system with similar cell parameters: a = 13.8268(1) ?, 13.7624(1) ?, 13.5917(1) ? or 13.5834(1) ? for M = Mn, Co, Ni or Cu, respectively and eight formula units per cell. Their structure closely related to that of pollucite, is built up from [M2/3,Fe1/3]O4 tetrahedra connected to each other through the common corners with PO4 tetrahedra. The resulting anionic three-dimensional framework leads to the formation along [1 1 1] direction, of channels where the large cesium ions occupy two independent crystallographic sites. A M?ssbauer study at room temperature, confirmed the +3 oxidation state of iron and its tetrahedral coordination. Diffuse reflectance spectroscopy also confirmed the occurrence of isolated Fe3+ ions: low energy gap due to oxygen to iron (III) inter-electronic transition and absence of d-d transition linked to iron; the colorimetric properties of the compounds were shown to be mainly governed by the visible d-d transitions linked to the M2+ cation in tetrahedral coordination. Magnetic susceptibility measurements reveal that the title compounds are weakly magnetically ordered at very low temperature due to super-superexchange magnetic interaction. The thermal evolution of χm follows in a wide temperature range, a Curie-Weiss law χ = C/(T-θ) with θ = -59, -36, -50 and -39 K for Mn, Co, Ni and Cu phases, respectively.
关键词： iron phosphates,M?ssbauer spectroscopy,optical properties,magnetic properties,pollucite structure
更新于2025-09-09 09:28:46