A sustainable reaction process for phase pure LiFeSi2O6 with goethite as an iron source

Lithium-iron methasilicate (LiFeSi$_{2}$O$_{6}$, LFS), a member of clinopyroxene family, is an attractive compound for its multiferroic properties and applicability in energy-related devices. Conventional preparative method requires heating at elevated temperatures for long periods of time, with inevitable severe grain growth. We demonstrate that α-FeO(OH) (goethite) is superior as an iron source toward phase pure LFS over conventional hematite, α-Fe$_{2}$O$_{3}$. The exact phase purity, i.e., no trace of iron containing reactant, is confirmed in the goethite-derived LFS by 57Fe Mössbauer spectroscopy. The grain growth of LFS during heating is suppressed to keep its crystallite size of 120 nm. Higher reactivity of goethite in comparison with hematite is mainly attributed to the dehydration of goethite, which in our case was accelerated by Li$_{2}$O. Related reaction mechanisms with the possible product pre-nucleation during mechanical activation are also mentioned. The magnetic properties of goethite-derived LFS are equivalent to those prepared via a laborious solid-state route. Thus, the presented preparative method offers a more sustainable route than conventional processing, and thus enables practical application of LFS

Evolution of the fishtail-effect in pure and Ag-doped MG-YBCO

We report on magnetic measurements carried out in a textured YBa$_2$Cu$_3$O$_{7-\delta}$ and YBa$_2$(Cu$_{1-x}$Ag$_x$)$_3$O$_{7-\delta}$ (at $x \approx$ 0.02) crystals. The so-called fishtail-effect (FE) or second magnetization peak has been observed in a wide temperature range 0.4~$<T/T_c<$~0.8 for $\textbf{H}\parallel c$. The origin of the FE arises for the competition between surface barrier and bulk pinning. This is confirmed in a non-monotonically behavior of the relaxation rate $R$. The value $H_{max}$ for Ag-doped crystals is larger than for the pure one due to the presence of additional pinning centers, above all on silver atoms.Comment: 6 pages, 6 figure

Nanostructure and Magnetic Anomaly of Mechanosynthesized Ce1-xYxO2-δ (x ≤ 0.3) Solid Solutions

Electromagnetic properties of complex oxide solid solutions containing Ce and Y attract increasing interests due to their high application potential. Their properties are known to be dependent on many factors including grain size and crystal defects. Here we focus on unique features of nanocrystalline Ce1-xYxO2-δ (x ≤ 0.3) solid solutions prepared via a mechanosynthesis. Mechanically activated CeO2-δ and mechanosynthesized Ce1-xYxO2-δ exhibit room-temperature ferromagnetism. The saturation magnetization reaches maximum for the Ce0.9Y0.1O2-δ solid solution. XPS and Raman spectra show that Ce4+ ions are partially reduced to Ce3+, with simultaneous introduction of oxygen vacancies accumulated on surface of the solid solutions. An analysis of the experimental magnetization data and the determination of both the spin state and the concentration of magnetic carriers revealed that a small part of the Ce3+ spins (&lt;1%) is responsible for the magnetic state of the Ce1-xYxO2-δ system. Existence of clusters with a short-range antiferromagnetic order is also suspected. © 2020 Elsevier LtdThe present work is supported by the APVV (project 19-0526 ), EUREKA (project E!9982 ) and the VEGA (project 2/0055/19 ). A. Ye. thanks the State Assignment (Theme “Magnit” No. АААА-А18-118020290129-5) for financial support. H.K., K.L.S. and M.S. are grateful to the National Scholarship Program of Slovakia ( SAIA, n. o.). V.Š. acknowledges the support by the DFG (project SE 1407/4-2 )

Changes in YBCO Single Grain Bulk Superconductor Exposed to Air Moisture

Changes in bulk single grain YBCO superconductor at exposition to air were studied. The increase of the sample weight caused by reaction with air moisture was observed by weighing the samples over two months period. Thermal analyses and mass spectrometry of the exposed samples has shown evolution of water and oxygen during sample heating. Observation with scanning electron microscope confirmed the formation of some nanosize phases at the inner sample surfaces. XPS spectra done on the freshly cleaved and on the air exposed (001) surfaces confirmed changes in Ba and Cu bonds. Observed structural changes did not caused systematic changes in measured trapped field

Space weathering of asteroidal surfaces

Context. The surfaces of airless bodies in the Solar System are continuously altered by the bombardment of micrometeoroids and irradiation by solar wind, flares, and cosmic particles. Major effects of this process – space weathering – are darkening and “reddening” of the spectra of surface materials, as well as a “degrading” of absorption features. Aims. We studied the changes induced by energetic ion irradiation in the ultraviolet-visual-near-infrared (UV-Vis-NIR) (0.2–0.98 μm) reflectance spectra of targets selected to mimic the surfaces of airless bodies in the inner Solar System. Our chosen targets are olivine pellets, pure or covered by an organic polymer (polystyrene), which is transparent before irradiation. Polystyrene is used as a template for organic matter of low volatility that can be present on asteroidal surfaces. Moreover we measured the changes induced by ion irradiation in the absorption coefficient of the polymer. The purpose was to have a tool to better compare laboratory with observed spectra and distinguish between planetary objects with pure silicate surfaces and those whose surface is covered by organic matter exposed to cosmic ion bombardment. Methods. The samples were irradiated in vacuum, at room temperature, with 200 keV protons or 200–400 keV argon ions. Before, during, and after irradiation diffuse reflectance spectra were acquired. Polystyrene films were also deposited on quartz substrates and irradiated while transmittance spectra were recorded. Results. We measured the variations of the absorption coefficient of polystyrene as a function of ion fluence. We showed that after ion irradiation the diffuse reflectance spectra of the samples covered by organics exhibit a much more significant variation than those of pure silicates. The spectra of targets made of olivine plus polystyrene can be fitted by using the measured absorption coefficient of polystyrene. Conclusions. The results obtained for pure olivine extend to the UV the spectral range of previous experiments. The data concerning the absorption coefficient of polystyrene are available on our web site (http://web.ct.astro.it/weblab/dbindex.htm

Elimination of oxygenation cracks in top-seeded melt-growth YBCO superconductors by high pressure oxygenation

International audienc

Thermal and energetic processing of astrophysical ice analogues rich in SO 2

International audienc

Oxygenation mechanism of TSMG YBCO bulk superconductor

International audienc

Study of the Mechanochemical Reduction of Ilmenite Concentrate by Addition of Aluminum

Mechanochemical reduction of ilmenite concentrate $(FeTiO_{3})$ with elemental aluminum powder was performed by high-energy milling in an industrial eccentric vibratory ball mill ESM 656-0.5 ks (Siebtechnik, Germany). The mechanochemically reduced ilmenite with various times of milling was characterized by X-ray diffraction analysis, which confirmed the presence of the $Al_2O_3$ and $Fe_2Ti$ phases after 120 min of milling. Thermal analysis evidenced the completion of a mechanochemical reduction during milling. After 360 min of milling, the $Fe_2Ti$ phase decomposed to α-(Fe,Ti) alloy, which was proven by $\text{}^{57}Fe$ Mössbauer spectroscopy. X-ray photoelectron spectroscopy detected the amorphous TiO phase in product after mechanochemical reduction, which is in accordance with thermodynamic prediction. Decreasing of specific surface area after 60 min of milling resulted from growing layers of the solid products of $FeTiO_3$ mechanochemical reduction