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.

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

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.

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.

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.

Two-dimensional materials are currently among the most intensively studied topics in condensed matter physics because of their intriguing properties and the possibilities of integration in future electronic device applications. Image potential states, i.e. two-dimensional unoccupied electronic states that are confined in front of a surface, can provide detailed information on work function, electric field effects, charge transfer, charge injection, and charge dynamics at surfaces. This information is essential to understand and tailor the properties of twodimensional materials for electronic device applications. In this work, we briefly review recent developments in the detection and analysis of image potential states in single- and multilayered two-dimensional materials, heterostructures thereof, and nanostructures, such as nanoislands and nanoribbons. We also address several issues that can have an effect on image potential states, such as the preparation method, quality of the material, defects, interfacial interactions, and interactions with the substrate.

In view of their potential applicability in technology fields where magnets are required to operate at higher temperatures, the class of nanocomposite magnets with little or no rare earth (RE) content has been widely researched in the last two decades. Among these nanocomposite magnets, the subclass of magnetic binary systems exhibiting the formation of L10 tetragonal phases is the most illustrious. Some of the most interesting systems are represented by the Mn-based alloys, with addition of Al, Bi, Ga, Ge. Such alloys are interesting as they are less costly than RE magnets and they show promising magnetic properties. The paper tackles the case of MnGa binary alloys with various compositions around the Mn3Ga stoichiometry. Four MnGa magnetic alloys, with Mn content ranging from 70 at% to 75 at% were produced using rapid solidification to form the melt. By combining structural information arising from X-ray diffractometry and transmission electron microscopy with magnetic properties determined by vibrating sample magnetometry, we are able to document the nature and properties of the structural phases formed in the alloys in their as-cast state and upon annealing, the evolution of the phase structure after annealing and its influence on the magnetic behavior of the MnGa alloys. After annealing at 400 degrees C and 500 degrees C, MnGa alloys are showing a multiple-phase microstructure, consisting of co-existing crystallites of L10 and D022 tetragonal phase. As a consequence of these structurally and magnetically different phases, co-existing within the microstructure, promising magnetic features are obtained, with both coercive fields and saturation magnetization exceeding values previously reported for both alloys and layers of MnGa.

We explored the possibility to guide the forming process in a Ta/TiO2/Pt memristive device using an X-ray nanopatterning procedure, which enables the manipulation of the oxygen content at the nanoscale. The irradiation of selected areas of the sample by a 65 x 58 nm2 synchrotron X-ray nanobeam locally generated oxygen vacancies which resulted in the formation of a conductive filament in the desired position in the material. The subsequent application of an electric field between the electrodes was exploited to achieve reversible bipolar resistive switching. A multitechnique characterization was then performed, highlighting a local increase in the height of the crystal and the formation of a dislocation network, associated with the presence of Wadsley defects. Our results show that X-ray nanopatterning could open new avenues for a more deterministic implementation of electroforming in oxide-based memristive devices. We tuned the oxygen content in a Ta/TiO2/Pt memristive device at the nanoscale by a synchrotron X-ray nanobeam. We obtained a conductive filament of oxygen vacancies in the desired position in the material to achieve a controlled resistive switching.