National Institute Of Materials Physics - Romania

This work investigates the influence of composition on the thermal properties of the high entropy alloy family Cu5Cr35Fe35V20-X-5 (at. %), where X = Ti, Ta, W or Mo in the framework of acting as a thermal barrier between the W-based plasma-facing elements and the CuCrZr or Cu-based heat sink components of the fusion reactor. The alloys were produced by arc melting and their microstructure and mechanical properties were previously characterized by XRD, SEM, and Vickers hardness measurements. Thermal properties have been measured on as-cast at thermally treated alloys using the laser flash method in the temperature range 25 degrees C to 600 degrees C to determine the thermal diffusivity, alpha, thermal conductivity, lambda, and specific heat, C-p. Dilatometry experiments were also carried out to obtain the linear thermal expansion coefficient, CTE, as a function of temperature. For all materials, the thermal conductivity increases with temperature from 15 W/mK at RT to 28 W/mK at 600 degrees C and does not significantly depend on the thermal treatment for the Mo-HEA and W-HEA, but increases after aging for the Ta-HEA and Ti-HEA. These values are lower than those of W (similar to 122 W/mK at 600 degrees C) and much lower than for CuCrZr-IG (similar to 354 W/mK at 400 degrees C). The thermal expansion coefficients of these HEAs, similar to 10 x 10(-6) degrees C-1 at RT and similar to 2 x 10(-6) degrees C-1 at 650 degrees C are between those of CuCrZr and the W for the entire operative temperature range. These results indicate that the Cu5Cr35Fe35V20-X-5 (X = Ti, Ta, W, Mo) HEAs have a promising combination of the thermophysical properties, lambda, C-p and CTE, to act as thermal barrier in plasma-facing components that require the union of W- and Cu-based materials.

Among many iron-based superconductors, isovalently substituted BaFe2(As1-xPx)2 displays, for x approximate to 0.3, apart from the quite usual Second Magnetization Peak (SMP) in the field dependence of the critical current density, an unusual peak effect in the temperature dependence of the critical current density in the constant field, which is related to the rhombic-to-square (RST) structural transition of the Bragg vortex glass (BVG). By using multi-harmonic AC susceptibility investigations in three different cooling regimes-field cooling, zero-field cooling, and field cooling with measurements during warming up-we have discovered the existence of a temperature region in which there is a pronounced magnetic memory effect, which we attributed to the direction of the structural transition. The observed huge differences in the third harmonic susceptibility at low and high AC frequencies indicates the difference in the time-scale of the structural transition in comparison with the timescale of the vortex excitations. Our findings show that the RST influence on the vortex dynamics goes beyond the previously observed influence on the onset of the SMP.

In the present work, we report the synthesis and investigations of La0.9K0.1MnO3 and La0.8K0.1Pb0.1MnO3 bulk samples which could be potential magnetocaloric materials for magnetic refrigeration close to room temperature. A flash combustion reaction and sintering at 1200 degrees C for 10 h are used to prepare the bulk materials. Both compounds crystallized into a rhombohedral structure with R3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\overline{3 }$$\end{document}c space group confirmed by X-ray powder diffraction results. Scanning electron microscopy analysis, combined with XRD peak profiles is performed to estimate the particle/crystallite size of the samples. Moreover, the Curie temperature, TC, is found to be higher in lead-rich sample due to the enhancement of the grain size and the Mn3+-O-Mn4+ double exchange (DE) interaction. Therefore, the bulk sample La0.8K0.1Pb0.1MnO3 shows a room temperature phase transition of 289 K as well as a higher saturation magnetization. The La0.8K0.1Pb0.1MnO3 bulk compound exhibits a high and sharp peak in magnetic entropy change up to 5.5 Jkg-1 K-1 under 5 T at the magnetic transition temperature TC. To compare the magnetocaloric performances of the studied compounds, relative cooling power (RCP) was employed. The obtained experimental results revealed that the increase in particle size influences severely the magnetocaloric properties.

This study investigates polycrystalline samples of TiFe2-xRexSn (with x = {0, 0.02, 0.04, 0.06, 0.2}) synthesized using conventional arc-melting and spark plasma sintering. Structural and morphological analysis shows that low Re substitutions result in good phase purity with minor traces of secondary phases, while higher Re content leads to the segregation of additional phases. The magnetism and electrical resistivity of the samples are affected by inherent Fe-Ti atomic disorder, with the effects of secondary phases becoming more prominent in the samples with higher Re content. The Seebeck coefficient values increase only for TiFe1.98Re0.02Sn, while the power factor increases for x = {0, 0.02, 0.04}, reaching maximal values for x = 0.02 at similar to 300 K and x = 0.04 at similar to 325 K, i.e., (2.22 +/- 0.2) x 10(-4) Wm(-1) K-2. The thermal conductivity of the samples increases with x, resulting in modest values of the figure of merit, with the maximum achieved for x = 0.02 at 325 K, i.e., 0.015 +/- 0.002. (c) The Author(s) 2024

Fabrication aspects of PdO thin films and coatings are reviewed here. The work provides and organizes the up-to-date information on the methods to obtain the films. In recent years, the interest in Pd oxide for different applications has increased. Since Pd can be converted into PdO, it is instructive to pay attention to the preparation of the pure and the alloyed Pd films, heterostructures, and nanoparticles synthesized on different substrates. The development of PdO films is presented from the early reports on coatings' formation by oxidation of Pd foils and wires to present technologies. Modern synthesis/growth routes are gathered into chemical and physical categories. Chemical methods include hydrothermal, electrochemical, electroless deposition, and coating methods, such as impregnation, precipitation, screen printing, ink jet printing, spin or dip coating, chemical vapor deposition (CVD), and atomic layer deposition (ALD), while the physical ones include sputtering and cathodic arc deposition, laser ablation, ion or electron beam-induced deposition, evaporation, and supersonic cluster beam deposition. Analysis of publications indicates that many as-deposited Pd or Pd-oxide films are granular, with a high variety of morphologies and properties targeting very different applications, and they are grown on different substrates. We note that a comparative assessment of the challenges and quality among different films for a specific application is generally missing and, in some cases, it is difficult to make a distinction between a film and a randomly oriented, powder-like (granular), thin compact material. Textured or epitaxial films of Pd or PdO are rare and, if orientation is observed, in most cases, it is obtained accidentally. Some practical details and challenges of Pd oxidation toward PdO and some specific issues concerning application of films are also presented.

In this work, single-phase Te-doped CoSb3 polycrystalline bulk (Indium powder) and nanocomposites (alpha-WC nanopowder) were synthesized via a ball milling, hand-grinding and consolidated by spark plasma sintering technique. The thermoelectric and mechanical characteristics of as-synthesized composites were studied. The electrical resistivity varies between 11.82 and 12.82 mu Omega-m for CoSb2.875Te0.125 + x (x = 0.33% In, 1% In, 2% In, 4% In and 1% In + 0.33% alpha-WC, respectively) composites. At temperature of 300 K, composite with x = 1% In exhibit the lowest resistivity of 11.82 mu Omega-m. Also, negative values of Seebeck coefficients confirm that electrons are the predominant charge carriers. The maximum power factor of 2566 and 2482 mu Wm-1 K-2 are observed from x = 1% In and x = 1% In + 0.33% alpha-WC composites at 673 K, respectively. Notably, the power factor of 1% In and 1% In + 0.33% alpha-WC composites is slightly higher (1.05 times) than the CoSb2.875Te0.125 sample. The composites with lowest weight percent of 1% In and 1% In + 0.33% alpha-WC have a considerably improved power factor. For the composite with x = 1% In + 0.33% alpha-WC, the minimum thermal conductivity of 2.32 W/m-K at 300 K was achieved through a combination of doping and dispersion in the CoSb2.875Te0.125 matrix. It is possible that the multi-scale size distributions of grains will reduce the lattice thermal conductivity by scattering phonons over a large wavelength range. As a result, an increased figure of merit of 0.82 was achieved for CoSb2.875Te0.125 + 1% In + 0.33% alpha-WC composites at 823 K. The results suggest that the doping with composite approach could boost thermoelectric efficiency in n-type CoSb3-based materials.

Fe, Co and Si powders were exposed to mechanochemical activation by high-energy ball milling for 0, 2, 4, 8 and 12 h. The samples were subsequently characterized by Mossbauer spectroscopy, X-ray powder diffraction (XRPD), magnetic measurements and optical diffuse reflectance spectroscopy. The room temperature Mossbauer measurements were consistent with the occurrence of FeCo2Si and Fe0.5Co0.5Si crystalline phases. The low temperature Mossbauer spectra confirmed the absence of superparamagnetism up to 44 K in the milled system. XRPD patterns supported the phase sequence derived from Mossbauer spectroscopy. The coercive field was found to increase with the ball milling time (BMT). Zero-field-cooling-field-cooling (ZFC-FC) measurements performed at 200 Oe in the temperature range 5-300 K evidenced the transition to the skyrmion phase of the Fe0.5Co0.5Si material below the critical temperature of 44 K. The optical absorption in the UV-Vis-NIR region of the spectrum was found to increase with BMT.

The Inconel 718 superalloy, a precipitation-hardenable material, is of particular interest for applications involving components operating under extreme conditions due to its excellent mechanical properties, high corrosion resistance at temperatures up to 700 degrees C, and good workability. At high temperatures, thermal transfer processes are crucial for temperature distribution across the component's section, structural transformations, and variations in the alloy's properties. The history of accidental overheating events is critical for the microstructure and properties of the alloy. Studies on thermal transfer in the Inconel 718 alloy available in the literature typically focus on the alloy in its as-delivered state. The experimental research presented in this paper examines the influence of repeated overheating history on the thermal diffusivity of the alloy.