National Institute Of Materials Physics - Romania

Superconducting bulk disks, of 20 mm in diameter and similar to 3.5-mm thickness of MgB2 were prepared by spark plasma sintering. Samples are co-added with 10 wt. % hexagonal BN (h-BN) or graphene (G) and other additives (B4C, Te, cubic BN, fullerene C-60, or Repa-C6H10O7Ge2 (GEP)), where h-BN and G are introduced in the composite to provide full machinability by chipping of the composite and the other additives to modify microstructure and superconducting characteristics. Measurements of trapped magnetic field B-tr for a fixed rate of the applied magnetic field decrease (0.00015 T/s) indicate that samples with G show less flux jumps, but a higher thermomagnetic stability is accompanied by lower values of B-tr than for samples with h-BN. The highest maximum B-tr at 12 K for samples added with h-BN or graphene was recorded for MgB2(Te)(0.01) + 10wt.% h-BN (3.48 T) and MgB2(B4C)(0.01) + 10wt.% G (2.73 T), respectively. These values of maximum trapped field were determined for an applied field of - 2.5 and - 1.8 T. Results suggest that machinable MgB2-based composites show potential for bulk superconducting magnet applications.

Exchange biasing of oxide-DMSs (dilute magnetic semiconductors) in exchange bias nanostructures, which are essential for use in spin-based electronic devices, presents a challenge because, in the available literature, exchange coupling typically occurs between secondary phases, with oxide-DMS not being involved. The experimental results presented in this study are consistent with the participation of Fe-doped ZnO (oxide-DMS) as a ferromagnetic (FM) component in the exchange bias (EB) of the ZnFeO system. The study was conducted on ZnFeO nanostructured systems with a 2 at% iron concentration, which were processed by the decomposition of Zn-Fe-propionates and annealing in an Ar-5%H-2 atmosphere at temperatures between 480 degrees C and 510 degrees C and times between 60 min and 100 min. The magnetization investigations support the coexistence of an FM phase with a Curie temperature above 300 K, an antiferromagnetic phase with a Neel transition, T-N, at about 200 K and a disordered spin-glass-like phase with a transition, T-SG, at about 50 K. All samples show the EB effect, characterised by a high EB blocking temperature, T-B approximate to 200 K, and/or a low EB blocking temperature, T-B approximate to 50 K. The analysis of experimental data provides evidence for the exchange biasing of Fe-ZnO (oxide-DMS) by the FeO (AFM) phase and/or SG phase. The exchange-biasing of Fe-ZnO oxide-DMS is promising for developing new materials (e.g., FM electrodes) to improve the efficiency of injecting highly spin-polarised currents in spintronic devices and to increase the device operating temperature.

Design of products involves functional and sensory aspects, where surfaces play an important role. This study uses (i) sensory attributes to show that tactile sensation is highly dependent on surface roughness, and (ii) variation in pupil diameter to suggest that roughness close to fingerprint geometry causes less arousal. A panel of over 30 participants explored six plexiglass surfaces with different roughness generated by variations in milling speed and depth. The pattern obtained on the samples is periodic in one direction, with an average wavelength between 113 mu m to 600 mu m and an average height between 13 mu m and 123 mu m. During a blind touch, the sensory attributes of smoothness, grip and quality of each sample were evaluated by the panellists, as well as the emotional attributes of valence and arousal. The evolution of pupil diameter over time was also recorded, and its average value during the first two seconds of touch was considered as a new emotional attribute. These attributes made it possible to calculate six centred indicators, ranging between -1 and 1, for each panellist and each sample. Statistical analysis of these indicators showed that the declared valence is correlated with smoothness, grip, and quality, all gradually decreasing as roughness increases. These results will allow product designers to improve the hedonic experience of future users. To more precisely analyse arousal, valence, and the evolution of pupil diameter, three of the six samples, manufactured with the same cutting tool, were considered. Valence and arousal appeared relatively difficult to verbalised, but the pupil diameter allowed the samples to be discriminated. The sample with a roughness close to the geometry of the fingerprint appeared to be the least emotional.

Within the framework of the EUROfusion Consortium, the Characterization of armour, heat sinks materials and joints sub-project of the Work Package Material (WP-MAT) has been dedicated to the development of different tungsten (W) monoblock mock-ups equipped with advanced materials for divertor target applications in the EUDEMO fusion reactor. Assessing the status of the relevant joining interfaces of these mock-ups, not only after fabrication but throughout the whole component lifetime, plays a key role in the qualification process. At the ENEA Special Technologies Laboratory (TES), a number of facilities have been built to perform non-destructive inspections of plasma-facing components for fusion applications by ultrasonic testing (UT). The present work reports on the results of the UT inspections assessing the structural integrity of the relevant joining interfaces of three small-scale mock-ups provided with advanced W armour materials, specifically W-matrix with W2C inclusions consolidated by Spark Plasma Sintering (SPS), K-doped rolled W and K-doped laminated W. The UT examinations are carried out after fabrication and after the high heat flux tests (HHFT) at the neutral beam facility GLADIS. All results confirm the high-quality joining achieved by HIP and HRP. During the HHF tests of mock-ups, after a few hundred HHFT cycles defects are detected at the joining interfaces, due to debonding, delamination and W material cracks mainly affecting the loaded zone. The ultrasonic pulse-echo technique provides not only the size and position of the defects in the plane orthogonal to the ultrasonic beam, but also their depth in the material. During the analysis, the probe is inserted inside the pipe and the mock-up is examined in a cylindrical configuration. The coupling medium (demineralized water) is poured only inside the pipe. The main inspection parameters and the piezoelectric probes are chosen to obtain the maximum resolution in accordance with the thickness and joining interfaces to be analyzed.

MgB2 is a perspective superconductor for many power applications. How this potential refers also to microwave or radiofrequency applications is still to be determined. Although its ultimate surface resistance in zero field is not competitive with conventional metallic superconductors, its strong pinning properties can favor RF applications in a dc magnetic field. Nonetheless, the RF response in the vortex state has been relatively less studied, as well as the effect of artificial pinning centers on the microwave surface resistance in the mixed state. In this paper we study the surface resistance of spark-plasma-sintered MgB2, with and without Te and cubic-BN (cBN) addition, in a dc magnetic field up to 1.2 T. We summarize previous results on pure MgB2, and we present new data on Te-and cBN-added MgB2. We use a two-tone dielectric-loaded resonator to measure the field-dependent surface resistance at 16.5 and 26.7 GHz in the temperature range from 10 K to T. By exploiting the simultaneous measurements at two frequencies, we extract the flux-flow resistivity, the pinning constant kp and the depinning frequency fp. The two-band nature of MgB2 affects the field dependence of the flux-flow resistivity. The microscopic superconducting state is not affected by the addition of artificial pinning centers, indicating that Te and cBN do not affect interband or intraband scattering. Pinning shows a measurable trend towards an increase in the Te-and cBN-added samples at higher temperatures and fields. We finally compare the results to those obtained in bulk Nb3Sn, also in view of possible in-field RF applications such as microwave cavity-based haloscopes.

The Ni49+xMn32-2xGa19+x (x = 0; 2) Heusler ferromagnetic shape memory alloys were prepared using spark plasma sintering using raw flake-type powders obtained by soft grinding melt-spun ribbons. Samples were characterized using x-ray diffraction, electron microscopy, thermal analysis, and bending tests. Although the properties of ribbons and corresponding powders show similar properties' tendencies, they are opposite in the bulk sintered alloys when compared with precursor powders. Namely, Ni49Mn32Ga19 bulk shows a higher enthalpy (5.8 J g-1), an increased martensitic transformation (MT) temperature (by 9 K), and a reduced hysteresis span (5 K). Conversely, for the Ni51Mn28Ga21 sintered sample, a lower enthalpy (2 J g-1), a significant decrease (by 40 K) in the MT starting temperature, and a broadening of the hysteresis range (26 K) were observed. This difference is analyzed versus specific features of the microstructure. Moreover, the activation energy and the pre-exponential factor of the MT, extracted through kinetic analysis within two non-isothermal models, Kissinger and Friedman, complement and sustain these findings. Fractography details of the sintered samples are discussed in relation to the stress-strain curves from the bending tests. The Ni49Mn32Ga19 bulk sample exhibits a higher bending strength (260 MPa) and a lower strain (0.55%) than the Ni51Mn28Ga21 sample (177 MPa and 0.61%). The observed dependence of functional characteristics on preparation enables the possibility of property control required for various applications and suggests that the proposed route is promising in this regard for further investigations.

A multiphase high-entropy diboride (Ti0.25Ta0.25Hf0.25Zr0.25)B2 is obtained by spark plasma sintering from a mixture of single-metal diborides. The as-prepared material at the microscale can be defined as a composite where grains of a Ta-rich/Ti-poor complex diboride phase are the reinforcement and grains of Ta-poor/Ti-rich complex diboride are the matrix. However, at the nanoscale, the grains are heterogeneous, composed of regions with a multitude of complex diboride compositions. The interface between nanoregions is compositionally graded and has an irregular shape. The four-metal diboride shows a deformation-resistant mechanism under bending load. A strengthening process is active, increasing the room temperature bending strength (326 MPa) by approximate to 50% at 1800 degrees C (488 MPa). A ductile behavior with a deformation strain of approximate to 7.5% is observed at 2000 degrees C while bending strength (407 MPa) is approximate to 25% above the value at room temperature. At 2000 degrees C, observation of dislocations propagating from one compositional nanoregion to another and with a different density suggests dislocation contribution, first of all, to plasticity. The peculiar heterogeneity of this material at nano- and microscales is considered the reason for the remarkable mechanical response to bending load at different temperatures.

The search for advanced materials has been growing, and high entropy alloys (HEAs) are emerging as promising candidates for application in the fusion domain. This work investigates the effect of Cr on the FeTaTiW medium entropy alloy to form (CrFeTaTi)70W30 high entropy alloy, comparing the experimental production and characterization with the simulation (molecular dynamics and hybrid molecular dynamics-Monte Carlo) of the phases formed. The alloys were produced by mechanical alloying and sintered by spark plasma sintering. Both simulations have shown that a body-centered cubic structure is formed for both compositions. Monte Carlo simulation provides a more precise prediction of microstructural formation and element segregation. Microstructural examination of the consolidated material revealed the presence of a W-rich phase and a Ti-rich phase, consistent with the phase separation observed in the MC simulations. Moreover, X-ray diffraction analysis of the milled powder for FeTaTiW and (CrFeTaTi)70W30 confirmed the formation of a bcc (body-centered cubic)-type structure with a low fraction of intermetallic phases. Mechanical testing showed ductile behavior at 1000 degrees C where (CrFeTaTi)70W30 showed a stress magnitude almost double that of FeTaTiW. Additionally, the thermal diffusivity between 20 and 1000 degrees C of both alloys increases as the temperature rises. (CrFeTaTi)70W30 exhibits an increase from 3 to 5 mm2/s, while FeTaTiW increases from 4 to 9 mm2/s. Still, both system's thermal diffusivity values are lower than those of CuCrZr and pure tungsten. Despite this, the study underscores the promising attributes of HEAs and highlights areas for further optimization to enhance its suitability for extreme conditions.

The field of newly developed two-dimensional (2D) materials with low symmetry and structural in-plane anisotropic properties has grown rapidly in recent years. The phosphorene analog of group IV monochalcogenides is a prominent subset of this group that has attracted a lot of attention because of its unique in-plane anisotropic electronic and optical properties, crystalline symmetries, abundance in the earth's crust, and environmental friendliness. This article presents a review of the latest research advancements concerning 2D group IV monochalcogenides. It begins with an exploration of the crystal structures of these materials, alongside their optical and electronic properties. The review continues by discussing the various techniques employed for the synthesis of layered group IV monochalcogenides, including both bottom-up methods such as vapor-phase deposition and top-down techniques like mechanical and/or liquid-phase exfoliation. In the final part, the article emphasizes the application of 2D group IV monochalcogenides, particularly in the fields of photocatalysis, photodetectors, nonlinear optics, sensors, batteries, and photovoltaic cells.

In recent decades, magnetic hyperthermia (MH) has gained considerable scientific interest in cancer treatment due to its ability to heat tumor tissues deeply localized inside the body. Functionalizing magnetic nanoparticles (MNPs) with vector molecules via specific organic molecules that coat the particle surface has enabled targeting particular tissues, thereby increasing the specificity of MH. MH relies on applying radiofrequency (RF) magnetic fields to a magnetic nanoparticle distribution injected in a tumor tissue. The RF field energy is converted into thermal energy through specific relaxation mechanisms and magnetic hysteresis-driven processes. This increases the tumor tissue temperature over the physiological threshold, triggering a series of cellular apoptosis processes. Additionally, the mechanical effects of low-frequency AC fields on anisotropic MNPs have been shown to be highly effective in disrupting the functional cellular components. From the macroscopic perspective, a crucial parameter measuring the efficiency of magnetic nanoparticle systems in MH is the specific absorption rate (SAR). This parameter is experimentally evaluated by different calorimetric and magnetic techniques and methodologies, which have specific drawbacks and may induce significant errors. From a microscopic perspective, MH relies on localized thermal and kinetic effects in the nanoparticle proximity environment. Studying MH at the cellular level has become a focused research topic in the last decade. In the context of these two perspectives, inevitable questions arise: could the thermal and kinetic effects exhibited at the cellular scale be linked by the macroscopic SAR parameter, or should we find new formulas for quantifying them? The present work offers a general perspective of MH, highlighting the experimental pitfalls encountered in SAR evaluation and motivating the necessity of standardizing the devices and protocols involved. It also discusses the challenges that arise in MH performance evaluation at the cellular level.