New Publications

https://doi.org/10.1007/s10973-023-12792-z

Samarium monosulfide, a strain gauge and barometric material, exists in equilibrium with Sm₃S₄ and Sm₂O₂S in the S-Sm–O system. Therefore, studying phase equilibria in the refractory Sm₂S_3-X-SmS-Sm₂O₂S system is a scientifically interesting task. In this system, 49 samples were synthesized and studied by powder XRD, differential scanning calorimetry, visual thermal analysis, and microstructural analysis. Melting points of Sm₃S₄, SmS, and Sm₂O₂S compounds were determined. Eutectic diagrams of Sm₃S₄-Sm₂O₂S, SmS-Sm₂O₂S, SmS-Sm₃S₄ systems were constructed. Temperatures and compositions of the binary eutectic points were determined. Fusion enthalpies for Sm₃S₄, SmS, and Sm₂O₂S phases were estimated using the Schröder–Le Chatelier equation. The liquidus lines were calculated using second-degree polynomials and Redlich–Kister model. Coordinates of the ternary eutectic point in the Sm₃S₄-SmS-Sm₂O₂S system were calculated using the cutting-plane method and the Scheffé method. The calculated compositions of ternary eutectic points were averaged at one most probable point, in accordance with the data on the samples microstructure. The experimental temperature of the ternary eutectic point coincides with the calculated values within the margin of error. Positions of eutectic valleys and approximate positions of isotherms in the system were established. Thermodynamic parameters of the α-Sm₂S₃ → γ-Sm₂S₃ polymorphic transition and the dependence of the Sm₂S_3-X composition on heat treatment conditions were determined. According to the scanning electron microscopy data, the approximate composition of the crystallized from the melt Sm₂S₃ sample is Sm₂S_2.95. The Sm₁₀S₁₄O phase decomposes at 1470 ± 15 °C in the course of a solid-phase reaction. The phase diagram of the Sm₂S_3-X-Sm₂O₂S system was revisited. Optical band gaps of Sm₁₀S₁₄O and Sm₂O₂S phases were determined. The Sm₁₀S₁₄O compound was optically characterized for the first time; its direct and indirect optical bandgaps were found equal to 2.48 and 2.37 eV, respectively. The determined direct and indirect optical bandgaps of Sm₂O₂S (4.4 eV and 3.95 eV, respectively) agree with the earlier measurements, thus confirming the accuracy of the chosen synthesis procedures.

https://doi.org/10.1016/j.nanoso.2023.101089

The results of a study of the dynamic (alternating current magnetic susceptibility) and static magnetic properties, as well as ⁵⁷Fe Mössbauer spectrometry and ferromagnetic resonance of two-line ferrihydrite nanoparticle systems with varying intensities of magnetic interparticle interactions are reported. The strength of the magnetic interparticle interactions has been tuned by coating (with various degrees of coating) the ferrihydrite particles (2–4 nm in size and an average size ∼2.7 nm) of the initial synthetic sample by arabinogalactan. Also, a biogenic ferrihydrite sample (an average particle size of 2-nm) with a natural organic coating was studied and it has the weakest magnetic interparticle interactions among of all the samples. Relaxation times of the particle’s magnetic moment were determined by the data of static and dynamic magnetic susceptibilities and from analysis of ⁵⁷Fe Mössbauer spectrometry. Based on the temperature dependences of the relaxation times, it has been concluded that the predominantly collective processes of freezing of the particle magnetic moments occur under the action of the magnetic interparticle interactions. It is shown that an important role in these processes is played by a magnetic subsystem of the surface spins of the particles. The effect of the interplay between the surface spin and magnetic moment subsystems on the static magnetic properties (low-temperature magnetic hysteresis loops) and the parameters of the microwave absorption line under the magnetic resonance conditions is discussed.