National Institute Of Materials Physics - Romania

The microscopic mechanism of the occurrence of ferroelectric properties in M-type barium hexaferrites is investigated by experimental and first-principle computation methods. The analysis of magnetic, X-ray, and Mossbauer measurements of BaFe12O19 samples ascertains the correlation between the thermal factor in the process of annealing samples and their functional properties. The occurrence of the remnant polarization in barium hexaferrites at room temperature contradicts the description of their crystal structure in the fra-mework of centrosymmetric space group P63/mmc (No. 194), in which one of the symmetry operations is inversion center. Therefore, the crystal structure of BaFe12O19 was analyzed in the frameworks of SG P63/mmc (No. 194) and non-centrosymmetric SG P63mc (No. 186). The computed value of polarization for a non-centrosymmetric unit cell is similar to 3.5 mu C/cm2. The analysis of polarization was carried out on a path connecting the polar P63mc and non-polar P63/mmc structures and considered in terms of the total energy barrier. Our result allows ascertaining a direct relationship between the remnant polarization of the unit cell and the broken spatial-inversion symmetry in the crystal structure of M-type barium hexaferrite.(c) 2022 Elsevier B.V. All rights reserved.

Cu2SnSe3 (CTSe) is a polyvalent material that can be used as an absorber layer for thin film solar cells or as a starting layer for the synthesis of CZTSe or CZTSSe compounds. Obtaining CTSe single phase films with opti-mized properties for thin film solar cells is a difficult task. A systematic study using both metallic and binary chalcogenides precursors for the formation of the CTSe phase was not performed. The films consisting of four different stacks (Sn\Cu, SnSe2\Cu, Sn\Cu2Se, and SnSe2\Cu2Se) were prepared by magnetron sputtering on soda lime glass (SLG) and molybdenum (Mo) coated SLG substrates, followed by annealing at 550 degrees C under Sn + Se atmosphere. X-ray diffraction and Raman spectroscopy results indicated the formation of a single CTSe phase in most of the stacks deposited on both substrates. Scanning electron microscopy images showed compact surfaces with large grains in the films deposited on Mo substrate, while the films on SLG have more voids on their sur-faces. The elemental analysis measured by energy dispersive spectroscopy revealed stoichiometric films on Mo, and copper and tin rich compositions on SLG substrates. The band gap values inferred by conventional spec-troscopy are between 0.81 and 1.95 eV. It was found that the SnSe2\Cu and Sn\Cu2Se stacks are preferred for the formation of a single CTSe phase, with dense surface morphology, a stoichiometric composition, and an optimal absorber layer band gap. This study opens the way to comprehend the formation reactions during the seleni-zation of metallic and binary chalcogenides precursors towards the optimization of kesterite absorber for photovoltaic device fabrication.

The aim of this paper is to provide a simple and efficient photoassisted approach to synthesize silver nanoparticles, and to elucidate the role of the key factors (synthesis parameters, such as the concentration of TSC, irradiation time, and UV intensity) that play a major role in the photochemical synthesis of silver nanoparticles using TSC, both as a reducing and stabilizing agent. Concomitantly, we aim to provide an easy way to evaluate the particle size based on Mie theory. One of the key advantages of this method is that the synthesis can be "activated" whenever or wherever silver nanoparticles are needed, by premixing the reactants and irradiating the final solution with UV radiation. UV irradiance was determined by using Keitz's theory. This argument has been verified by premixing the reagents and deposited them in an enclosed space (away from sunlight) at 25 degrees C, then checking them for three days. Nothing happened, unless the sample was directly irradiated by UV light. Further, obtained materials were monitored for 390 days and characterized using scanning electron microscopy, UV-VIS, and transmission electron microscopy.

The iron oxide nanoparticles coated with different surface coatings were studied and characterized by multiple physicochemical and biological methods. The present paper aims at estimating the toxicity in vitro and in vivo of dextran coated iron oxide aqueous magnetic fluids. The in vitro studies were conducted by quantifying the viability of HeLa cells after their incubation with the samples (concentrations of 62.5-125-250-500 mu g/mL at different time intervals). The estimation of the toxicity in vivo of administering dextran coated iron oxide aqueous magnetic fluids (DIO-AMF) with hydrodynamic diameter of 25.73 +/- 4 nm to Male Brown Norway rats has been made. Different concentrations (62.5-125-250-500 mu g/mL) of dextran coated iron oxide aqueous magnetic fluids were administered for 7 consecutive days. Hematology and biochemistry of the Male Brown Norway rats assessment was performed at various time intervals (24-72 h and 21-28 days) after intra-peritoneal injection. The results showed that high concentrations of DIO-AMF (250 and 500 mu g/mL) significantly increased white blood cells, red blood cells, hemoglobin and hematocrit compared to the values obtained for the control group (p < 0.05). Moreover, following the administration of DIO-AMF, the levels of alkaline phosphatase and aspartate aminotransferase increased compared to the control group (p < 0.05). After DIO-AMF administration, no significant difference was observed in the levels of alanine aminotransferase, gamma-glutamyl transpeptidase, urea and creatinine compared to the control group (p < 0.05). The results of the present study showed that dextran coated iron oxide aqueous magnetic fluids in concentrations lower than 250 mu g/mL are reliable for medical and pharmaceutical applications.

Multifunctional magnetic nanocomposites are among those heterogeneous nanosized systems where at least one phase component is magnetic and can act as an intermediate of either the actuation or the response of the overall system. The main advantage of heterogeneous nanosystems is the possibility of combining and inter-influencing the electronic properties of constituent interfaced nanophases. Consequently, unique physico-chemical properties of the hybrid materials of interest in various applications can be obtained. This Special Issue of Nanomaterials highlights the most advanced processing and characterization tools of some multifunctional magnetic nanocomposites and heterogeneous systems of interest in various applications, from biomedicine to sensoristics and energy-saving materials.

Hydrides have emerged as strong candidates for energy storage applications and their study has attracted wide interest in both the academic and industry sectors. With clear advantages due to the solid-state storage of hydrogen, hydrides and in particular complex hydrides have the ability to tackle environmental pollution by offering the alternative of a clean energy source: hydrogen. However, several drawbacks have detracted this material from going mainstream, and some of these shortcomings have been addressed by nanostructuring/nanoconfinement strategies. With the enhancement of thermodynamic and/or kinetic behavior, nanosized complex hydrides (borohydrides and alanates) have recently conquered new estate in the hydrogen storage field. The current review aims to present the most recent results, many of which illustrate the feasibility of using complex hydrides for the generation of molecular hydrogen in conditions suitable for vehicular and stationary applications. Nanostructuring strategies, either in the pristine or nanoconfined state, coupled with a proper catalyst and the choice of host material can potentially yield a robust nanocomposite to reliably produce H-2 in a reversible manner. The key element to tackle for current and future research efforts remains the reproducible means to store H-2, which will build up towards a viable hydrogen economy goal. The most recent trends and future prospects will be presented herein.

In this work, Tungsten(W)-doped TiO2 nanoparticles were synthesized using the sol-gel method and were used as electrode materials in supercapacitor applications. The structural and morphological properties of the prepared samples were analyzed by means of XRD, STEM, TEM, and XPS. The analysis of the defect centers was carried out using EPR spectroscopy. The electrochemical analysis of the assembled supercapacitor was done using cyclic voltammetry, galvanostatic cycling with potential limitation technique, potentiostatic electrochemical impedance spectroscopy, and voltage-holding experiments. All the presented samples showed paramagnetic defects in the EPR analysis, while 0.5% W-doped TiO2 showed a maximum signal intensity. The supercapacitor performance from the synthesized electrode material showed highly encouraging results. The equivalent series resistance (R-s) value for all the designs showed values under "1 omega,' which reflects high conductivity. As the maximum EPR intensity comes from TiO2 doped with 0.5% W, the supercapacitor performance of this sample was tested with a newly designed five-electrode system. This design showed superior performance compared to any other used designs with a specific capacitance of 25.5 F g(-1), with an energy density of 14.16 Wh kg (-1 )at 302 kW kg (-1).

Glassy nanocomposites containing Yb3+/Er3+-doped GdF3 and LiGdF4 nanocrystals have been prepared by controlled crystallization of the xerogel and the structural, up-conversion luminescence, and magnetic properties were analyzed and discussed. Structural and morphological analysis showed uniform distribution of both GdF3 and LiGdF4 nanocrystals (tens of nm size), embedded in silica glass matrix as the result of thermal decomposition of the trifluoracetates, revealed as a strong exothermic peak at about 300 degrees C; the Li-ions co-doping showed a strong influence on the GdF3 and LiGdF4 nanocrystalline fraction. The energy dispersive spectrometry mapping showed Gd, F and Yb, Er within the nanocrystals but not in the silica glass matrix. X-ray diffraction pattern analysis indicated the crystalline lattice distortion consistent with the Yb/Er incorporation in both fluoride nanocrystals. The "green" ((H-2(11/2), S-4(3/2)) -> I-4(15/2)) and "red" (F-4(9/2)-> I-4(15/2)) up-conversion luminescences at 525, 545, and 660 nm observed under 980 nm laser light pumping were assigned to the Er3+ ions deexcitation through a two-photon process. The magnetic properties of the nanocomposite are strongly temperature dependent. The magnetization hysteresis loops show a ferromagnetic behavior at low temperatures (5K) related to the rare-earth ions contribution and the saturation magnetization of 39 emu/g. At 300 K a paramagnetic behavior was observed that was ascribed to the non-interacting localized nature of the magnetic moment of the rare-earth ions. Hence, such novel, multifunctional magnetic and optical materials can allow the intertwining between magnetism and photonics and might offer new opportunities for new magneto-optical device development.

In this paper, we theoretically investigate the linear and nonlinear optical activity of polymers based on poly(ortho-anisidine) and polyaniline using density functional theory. The PBE0 exchange correlation functional is used to predict their dipole moment, mean polarizability, polarizability anisotropy, and the static first hyperpolarizability. The polymers show high hyper-Rayleigh scattering first hyperpolarizability, which make them suitable for nonlinear optical devices. The relationship between the first hyperpolarizability and the energy gap is also taken into account. [GRAPHICS] .

In our work, the kinetics of martensitic transformations and the influence of thermal treatments on martensitic transformations, as well as the related magnetic properties of the Ni49Mn32Ga19 ferromagnetic shape memory melt-spun ribbons, have been investigated. Thermal treatments at 673 K for 1, 4 and 8 h can be considered an instrument for fine-tuning the performance parameters of alloys. One-hour thermal treatments promote an improvement in the crystallinity of these otherwise highly textured ribbons, reducing internal defects and stress induced by the melt-spinning technique. Longer thermal treatments induce an important magnetization rise concomitantly with a slight and continuous increase in martensitic temperatures and transformation enthalpy. The activation energy, evaluated from differential scanning calorimeter experimental data with a Friedman model, significantly increases after thermal treatments as a result of the multi-phase coexistence and stabilization of the non-modulated martensitic phase, which increases the reverse martensitic transformation hindrance.