Nanoparticles of iron (α-Fe) and iron oxide (Fe
3
O
4
) with a core-shell structure (α-Fe core, Fe
3
O
4
shell) covered with additional graphite-like carbon layer have been synthesized. The samples ...were obtained by solid-phase pyrolysis of iron phthalocyanine (FePc) at a pyrolysis temperature of 1000°C, followed by annealing in an oxygen atmosphere at a temperature of 250°C. The composition, structure and morphology of the samples were investigated by transmission and scanning transmission electron microscopy with elemental mapping, synchrotron X-ray diffraction and Raman spectroscopy.
The anomalous-diffraction method applied near the absorption edge of Hf is used to investigate the features of atomic ordering in the Eu
2
Hf
2
O
7
structure. Structural parameterization describing a ...continuous transition between ideally disordered (fluorite) and ideally ordered (chalcolamprite) structures is proposed. A comparison between the calculated and experimental results demonstrates qualitative coincidence and confirms the hypothesis that the sample under study exists in the intermediate phase. The method is sensitive to cation ordering, but anion ordering of the suggested model is not described.
The shells of the chambered nautilus (
Nautilus pompilius
) are studied by X-ray structure analysis (XRD) and electron microscopy (SEM and TEM). The shell structure is examined in a nanometer scale ...using XRD and synchrotron-based small angle X-ray scattering (SAXS). The mineral composition of shells includes 98–99 wt % aragonite, ~1 wt % organic substance (conchiolin), 1 wt % strontianite, and 0.5 wt % calcite. Trace elements comprise Na, Mg, Al, K, Si, Fe, P, S, Zn, Sr, Ba, and Cl. The laminated layers are composed of aragonite crystals with a width of 5–10 μm and a thickness of 0.5–1 μm; the prismatic layers, with a length of 7–12 μm long and a width of 1–3 μm. According to XRD and SAXS assays, the aragonite layers are formed of flawless monocrystals lacking any internal structuring. The shell conchiolin is a polymer formed of a system of parallel fibers folded with a step of approximately 100 nm without longitudinal structuring. Presumably, the unique structure of the nautilus shells has determined the existence of Nautiloidea over 500 Ma and their preservation as fossils for over 100 Ma.
In-situ EXAFS combined with a Paris-Edinburgh press (PEP) is an outstanding tool to investigate the local environment of trace elements in melts at high pressure and temperature. A novel design of ...the pressure assembly ensures a highly stable experimental setup (reaching temperatures of up to 2000 K at 2.5 GPa) while permitting the necessary level of X- ray transmission. This study focuses on the structural incorporation of the geochemically important trace elements Y and Sr in sodium-rich silicate-carbonate melts. Y and Sr K edge EXAFS were collected in transmission mode of the melt (at ∼2.5 GPa, 1600 K) and its respective quench products. Distinct changes in the XANES region suggest a change in site symmetry during the cooling process.
The valence states and local structure around Mn atoms in mixed-valence Mn2BO4 have been studied by temperature dependent X-ray powder diffraction (XRPD), X-ray photoelectron (XPS) and Mn K-edge ...X-ray absorption (XAFS) spectroscopies measurements. X-ray absorption near-edge structure (XANES) and XPS have been used to measure the average oxidation state of Mn in bulk and near-surface of the material. The edge position, peak shapes and pre-edge features of Mn K-edge XANES spectra have been discussed. The pronounced temperature dependence of the Debye-Waller (DW) factor corresponding to the MnO coordination shell has been found from the extended x-ray absorption fine structure (EXAFS) analysis and has been associated with variations in the local distortions in MnO6 octahedra and emergence of short-range magnetic correlations at low temperatures. The XRPD measurements have been carried out at 298, 523 and 773 K. The monoclinic symmetry (P21/n) was found to persist up to highest temperature measured. The BVS calculations have revealed large valence difference between two manganese sites that strongly supports the presence of charge ordering up to high temperatures.
•The monoclinic symmetry was found to persist up to 973 K.•The large bond-valence difference between Mn1 and Mn2 sites suggests the presence of the charge ordering up to highest temperature measured.•The DW factor is progressively reduced below 100 K and goes through a minimum at the TN.•The average manganese oxidation state in bulk was found to be Mn(2.55±0.08)+.
•Single crystals of of the warwickites Mn2-xFexBO4 (x=0.3, 0.5, 0.7) have been synthesized.•Crystal and local atomic structure has been studied through X-ray diffraction and X-ray absorption ...spectroscopy.•The Fe-doping was found to enhance the magnetic frustation giving rise to the supression of the long-range magnetic order.
Single crystalline Mn2-xFexBO4 with x=0.3, 0.5, 0.7 grown by the flux method have been studied by means of X-ray diffraction and X-ray absorption spectroscopy at both Mn and Fe K edges. The compounds were found to crystallize in an orthorhombic warwickite structure (sp. gr. Pnam). The lattice parameters change linearly with x thus obeying the Vegard’s law. The Fe3+ substitution for Mn3+ has been deduced from the X-ray absorption near-edge structure (XANES) spectra. Two energy positions of the absorption edges have been observed in Mn K-edge XANES spectra indicating the presence of manganese in two different oxidation states. Extended X-ray absorption fine structure (EXAFS) analysis has shown the reduction of local structural distortions upon Fe substitution. The magnetization data have revealed a spin-glass transition at TSG=11, 14 and 18K for x=0.3, 0.5 and 0.7, respectively.
Bronze statues “John the Baptist” and “Dancing Cupid” from the collections of the Pushkin State Museum of Fine Arts have been investigated at the National Research Centre “Kurchatov Institute.” These ...statues were previously damaged in fire. Before carrying out restoration, it was necessary to perform their complex study, including identification of statue materials; elemental and phase analysis of contaminations; estimation of the state of surfaces and internal parts; and detection of technological elements, as well as hidden defects, corroded parts, and cracks. To this end, scanning electron microscopy with X-ray microanalysis, synchrotron radiation diffraction, and neutron radiography and tomography have been used.
Single‐crystalline MgFeBO4, Mg0.5Co0.5FeBO4, and CoFeBO4 have been grown by the flux method. The samples have been characterized by X‐ray spectral analysis, X‐ray diffraction, and X‐ray absorption ...spectroscopy. The X‐ray absorption near‐edge structure (XANES) and extended X‐ray absorption fine structure (EXAFS) spectra have been measured at the Fe and Co K‐edges over a wide temperature range (6.5–300 K). The composition, the charge state, and local environment of both Fe and Co atoms have been determined. The effects of Co substitution for Mg on the local structural distortions have been revealed experimentally and the MO bond anisotropy has been found.
A complex study of a spearhead dated back to IV mill. BC from burial mound no. 1 near Novosvobodnaya village (collection of the State Historical Museum) and, in particular, the material of spearhead ...superficial crust has been performed. The elemental and phase composition of the metal of spearhead and the superficial crust on its surface have been determined by scanning electron microscopy, jointly with energydispersive X-ray microanalysis and X-ray phase analysis. A comparative analysis of the results of studying the spearhead superficial crust and similar crusts on other artifacts from the mounds near Novosvobodnaya village suggest natural origin of the crust on copper‒arsenic artifacts.
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