National Institute Of Materials Physics - Romania

The present study is focused on describing the influence of the sintering method (fast field-assisted Spark Plasma Sintering vs. conventional sintering) on the functional properties of BaTi0.90Hf0.10O3 ceramics with polymorph superposition around room temperature. Dense ceramics, derived from nanopowders synthesized via Pechini method, with grain size downscaled from 3.7 to 0.07 mu m were prepared using different sintering strategies. XRD data at room temperature revealed the presence of mixtures of dissimilar structural modifications either for the starting nanopowder, as well as for the related ceramics. The Landau-based calculations indicated that different amounts of polymorphs are stable in these ceramics, by considering the grain size reduction and the strain-stress fields produced by the fast sintering method, thus confirming the experimental results of the structural and Raman analyses. By decreasing the average grain size from micro-to nanoscale, a slight decrease of the Curie temperature, accompanied by the increase of the diffuseness of the ferroelectric-to-paraelectric phase transition and the decrease of both the permittivity maxima and the dielectric losses was detected. Both the dielectric response and the ferroelectric P(E) loops indicated a ferroelectric-relaxor crossover as the grain size decreased in the nanometre range. The beneficial effect of the nanostructuring on the energy storage efficiency was also revealed.

Background . Algeria has long sought to exploit its uranium deposits in the Hoggar region, whose objective is to market the ore, and use part of the production exclusively in the civil field, especially in electricity generation. The exploitation and valorisation of this ore; require a very specific process of exploitation, characterization and treatment. The main objective of this work is to establish a detailed and complete technical data sheet for the Tahaggart deposit, enabling the implementation of a uranium ore mining and beneficiation technique to obtain a marketable product known as "yellow cake". Methods . To achieve this objective, samples were taken from the site understudy, followed by microscopic and macroscopic analyses non-thin sections to obtain petrographic, mineralogical and geochemical identifications. Results . The analyses confirmed the sandstone character of the ore and the predominance of quartz, clays, oxides and iron hydroxides as well as uranium and rutile minerals. The uranium contents in the mineralized altered levels varied from 0.90 to 1.32 and from 0.34 to 0.74 % in the mineralized conglomeratic sandstones. Uranium occurred either in the high-grade uranium minerals or low-grade apatite, zircon, rutile, and in traces in monazite. & Scy; o n c l u s ions . Different studies carried out on the Tahaggart region have proven the presence of Uranium ores with remarkable quantities, varying between 0.90 to 1.32 % in the mineralized altered levels and 0.34 to 0.74 % in the mineralized conglomeratic sandstones, however, despite this, and in view of the strategic value that uranium enjoys at the international level; to date, there is no exploitation this mine by the state. The best treatment method in this case is heap leaching; the recovery rate by this method can reach 70 % in uranium as "yellow cake".

Capitalizing on invasive plant species and stopping their aggressive spread might be achieved by using them as a renewable source of useful products such as cellulose. The study aimed to develop new cellulose-based food packaging materials with antioxidant and antimicrobial activity. The cellulose was extracted from the invasive plant species Robinia pseudoacacia pods, crosslinked with citric acid, used as reinforcement for polyvinyl alcohol (PVA) and functionalized with ferulic acid (FA). The obtained materials were characterized by XRD, ATR-FTIR, contact angle and SEM. The materials exhibited low solubility in water and the swelling degree was proportional to the FA content. The FA release from the matrix was assessed by HPLC and the antioxidant profile by CUPRAC, FRAP, and TEAC methods. The obtained materials inhibited the growth of bacteria, yeasts and molds, being especially active on Gram-positive bacteria and yeasts. Overall, the most promising formulation for further developing new packaging materials for products with water activity less than 0.95 was the one with the highest FA content.

Floquet topological insulators (FTIs) are materials which undergo topological phase transitions under a time periodic perturbation causing time reversal symmetry breaking. In this Letter, we propose a spin filter model based on a FTI realized by irradiating a honeycomb lattice with circularly polarized light, in the presence of intrinsic spin-orbit coupling. The main ingredient of our proposed mechanism of Floquet topological spin filter (FTSF) implementation is the presence of an on-site staggered potential which controls independently the topological phases of the two existent spin states. After giving a numerical example of the occurrence of the FTSF phase, we argue that the origin of the FTSF phase resides in the spatial inversion symmetry breaking due to the presence of a staggered potential. The light helicity degree of freedom may be used to select the filtered spin state. Moreover, due to the topological properties of our model, the spin will be purely filtered in a Hall transport experiment. We discuss also the experimental feasibility.

Cu2ZnSnSe4 (CZTSe) is a promising material for thin-film solar cells due to its suitable band gap, high absorption coefficient, and composition of earth-abundant and nontoxic elements. In this study, we prepared CZTSe thin films from Cu/SnSe2 and ZnSe stacks using a two-step annealing process. Initially, Cu-Sn-Se (CTSe) films were synthesized by sequential deposition and annealing of Cu and SnSe2 precursors in either a selenium (Se) or tin-selenium (Sn+Se) atmosphere. After the deposition of a ZnSe layer on top of CTSe films, the stack underwent a second annealing process, again in either a Se or Sn+Se atmosphere, resulting in four distinct annealing combinations: Se -> Se, Sn+Se -> Se, Se -> Sn+Se, and Sn+Se -> Sn+Se. The first annealing step enabled the formation of CTSe, while the second annealing step, performed after ZnSe deposition, led to the formation of the CZTSe phase. Comprehensive characterization including grazing incidence X-ray diffraction (GIXRD), Raman spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and electrical measurements was conducted. GIXRD and Raman analysis revealed kesterite CZTSe phase peaks, with some samples showing a split in the main peak at similar to 27 degrees (2 theta), indicating the presence of Cu x Se and ZnSe secondary phases. SEM analysis showed the impact of Sn and Se annealing on grain size, with larger grains observed in films annealed in Sn+Se atmospheres, particularly in the second heat treatment process. EDS results displayed consistent elemental composition across samples, with varying Cu/(Zn+Sn), Zn/Sn and Se/metal ratios influencing the band gap values from 1.09 to 1.63 eV. Hall measurements indicated p-type conductivity with carrier concentrations between 1016 and 1023 cm-3. These results highlight the effectiveness of our two-step annealing process, particularly the Sn+Se atmosphere, in optimizing CZTSe thin films for potential use in high-efficiency thin-film solar cells.

Potassium ions are important for developing electrode materials because they have similar properties to lithium and sodium ions. Mixed chromium phosphates (KMIICr(PO4)2) II Cr (PO 4 ) 2 ) with substituted M II sites using divalent elements (M = Ni, Co, Cu) were synthesized using a solid-state reaction method. The samples were analyzed using various techniques such as powder X-ray diffraction, Fourier transform infrared, Raman, and electron paramagnetic resonance spectroscopy. The proposed phosphates had a monoclinic phase structure with a P21/n 1 /n space group, and they contained large tunnels occupied by K+ + cations. The dielectric properties showed that the Ni-based phosphates had slower dielectric relaxation, while the Co and Cu-based phosphates had quicker polarization and depolarization processes. Additionally, the resistance of the grains decreased from Ni to Co to Cu-based phosphates, indicating easier charge movement in each material, consistent with the increase in conductive losses and a.c. conductivity when changing the M II ions.

Expression of concern for 'Iron oxide magnetic nanoparticles with versatile surface functions based on dopamine anchors' by Mykola Mazur et al., Nanoscale, 2013, 5, 2692-2702, https://doi.org/10.1039/C3NR33506B.

The spin frustration and other magnetic properties of the "cartwheel" heptanuclear cluster [FeIII 7O3(O2C t Bu)9(Me-dea)3(H2O)3] (Me-deaH2 = N-methyldiethanolamine) have been previously investigated; we present here a Mossbauer spectroscopic study and sub-Kelvin magnetization and ac susceptibility measurements which enable a complete magnetic picture of this frustrated cluster. 57Fe Mossbauer spectra above 150 K showed three doublets in a 1:3:3 ratio, which could be assigned by their respective quadrupole splittings to the central Fe(1) and the peripheral Fe(2) and Fe(3). The field dependence of the corresponding magnetic sextets at 3 K showed that the spins on the central Fe(1) and the three peripheral Fe(2) sites with O5N coordination are oriented mutually coparallel, while these are antiparallel to the spins on the peripheral Fe(3) sites with O6 coordination, resulting in an overall S = 5/2 ground state. This provides experimental confirmation of the previously proposed spin ground state structure. Upon cooling to sub-Kelvin temperatures, a crossover to spin blocking with T B approximate to 0.21 K could be observed. This single-molecule magnet behavior had been expected but had not been observable with a conventional SQUID. The anisotropy barrier, of 3-fold symmetry, can be described in terms of the parameter D/k B = -0.47 K and a fourth-order perturbation; the latter enables thermally activated quantum tunneling through the excited sublevel m z = +/- 3/2, with an activation barrier of U/k B = 1.9 K.

Kynurenic acid (KA) is an active metabolite of tryptophan with notable biological effects, such as antioxidant, neuroprotective, and anti-inflammatory properties. It often undergoes changes of the concentration in biological fluids in chronic diseases. Thus, detecting KA is of great importance for diagnosing inflammatory and neurodegenerative conditions, monitoring disease progression, and assessing responses to pharmacological treatment. This study aimed to design a tailored, flexible platform for sensitive and direct electrochemical detection of KA in biological fluids. Carbon-based electrodes were custom-printed in the lab using specialized inks and flexible substrates. The working electrodes were further functionalized with graphene oxide and subsequently electrochemically reduced to increase the sensitivity toward the analyte. An optimized differential pulse voltammetry protocol was developed for KA detection. The elaborated platform was firstly characterized and then evaluated regarding the analytical performances. It showed a good limit of detection (3 nM and demonstrated the capability to detect KA across a broad concentration range (0.01-500 mu M). Finally, the elaborated flexible platform, was succesfully applied for KA determination in serum and saliva samples, in comparison with an optimized HPLC-UV method. The developed platform is the first example of in-lab printed flexible platform reported in literature so far for KA detection. It is also the first study reported in the literature of detection of KA in raw saliva collected from 10 subjects. The sensitivity towards the target analyte, coupled with the adaptability and portability, showcases the potential of this platform for thus illustrating great potential for further development of wearable sensors and biomedical applications.