National Institute Of Materials Physics - Romania

Herewith, we investigated the capacitive properties of hybrid nanometric architectures consisting of tungsten oxide nanoparticles deposited on graphite (WOx/G) and graphite coated with highly-porous carbon nanowall layers (WOx/CNW/G). The deposition of the nanostructured oxide was performed by a plasma-assisted sublimation, vapor transport and condensation technique. The samples containing the CNW interlayer show superior areal capacitances making this architecture and its fabrication route promising approaches for supercapacitor applications. Thus, areal capacitances of WOx/CNW/G and WOx/G, estimated from galvanostatic chargedischarge tests (GCD) at an applied density current of 1 mA cm-2, are 1247.2 mF cm-2 and 527.3 mF cm-2, respectively. From SEM and XPS investigations, it was observed that CNW promotes the formation of a high amount of small tungsten oxide particles, homogeneously distributed on electrode surface, and facilitates the formation of highly conductive tungsten nitride species, resulting in electrodes with remarkable charge-storage capacity.

This work reports the design and synthesis of novel oxadiazole-decorated azobenzenes, structural analysis of the resulting compounds and behavior under light irradiation. The synthetic strategy involved constructing amino functionalized heterocyclic key intermediates which were used either to yield electrophilic diazonium salts able to react with phenol moieties or as nucleophilic partners in Bayer-Mills reaction with nitroso-substituted derivatives. The amino-derived oxadiazole intermediates were investigated by absorption and emission spectroscopy providing blue and green emitted light. The target oxadiazole-decorated azobenzenes were structurally characterized, including solid-state structures, and subsequently used in irradiation experiments in order to take advantage of the azo group known to provide photoswitching abilities. We noticed quenching of the emissive properties in presence of the azo group; however, all compounds were very stable to repeated cycles of light irradiation. In addition, according to structural diversification we could obtain half-lives of the meta stable isomers within hours to hundreds of hours range. The experimental results were very well correlated with DFT calculations. The synthesis of novel oxadiazole-decorated azobenzenes using amino functionalised heterocyclic intermediates used either to provide electrophilic diazonium salts able to react with phenols or as nucleophilic partners in Bayer-Mills reaction is reported in this work. The oxadiazole-decorated azobenzenes were used in irradiation experiments to determine the parameters that characterize a photoswitch, yielding appealing results. The experimental results were very well correlated with DFT calculations.+image

A critical brief review of the evolution of the ideas describing the matter, with emphasis on concepts relevant to the journal's goals: surfaces, interfaces, and interphases is presented. The complex relationship between interphase and interface, including the role of the submicron confinement on the physical and chemical properties of matter are analyzed from both theoretical and experimental standpoints. The most important consequences triggered by the recognition of interphases are briefly discussed. Most matter (at a macroscopic scale) is dominated by bulk behavior. The rapid advances in materials and especially the accelerated progress in the synthesis and characterization of submicron materials and associated technologies, labeled as the "nano revolution", revived the research on interfaces and interphases at atomic and molecular scales. It is suggested that interphase ignites a new kind of material, whose "bulk physical features" have been distorted by the submicron confinement. Such an "interphase surface" (for example a drop of gold with a diameter smaller than a few nanometers, or a few layers of graphene), may exist free standing and be stable. These materials, which no more exhibit the bulk properties will be tentatively referred to as "Sutter" ("Sutter" defines an abbreviation that involves both surface and matter concepts). Sutter is characterized by the fact that its physical and chemical properties are controlled by the interphase. It is concluded that Sutter is essentially a submicron phase of the matter, that exhibits size-dependent features. Sutter materials may be embedded in various materials (such as polymers, metals, and alloys) as nanocomposites, thus projecting specific features at the macroscopic scale. Most free standing interphases may be considered as Sutter materials or phases. The interface does not qualify as a Sutter material.

This study focuses on the properties of the BiOi (interstitial Boron-interstitial Oxygen) and CiOi (interstitial Carbon-interstitial Oxygen) defect complexes by 5.5MeV electrons in low resistivity silicon. Two different types of diodes manufactured on p-type epitaxial and Czochralski silicon with a resistivity of about 10 Omega center dot cm were irradiated with fluence values between 1x10(15) cm(-2) and 6x10(15) cm(-2). Such diodes cannot be fully depleted and thus the accurate evaluation of defect concentrations and properties (activation energy, capture cross-section, concentration) from Thermally Stimulated Currents (TSC) experiments alone is not possible. In this study we demonstrate that by performing Thermally Stimulated Capacitance (TS-Cap) experiments in similar conditions to TSC measurements and developing theoretical models for simulating both types of BiOi signals generated in TSC and TS-Cap measurements, accurate evaluations can be performed. The changes of the position-dependent electric field, the effective space charge density N-eff profile as well as the occupation of the BiOi defect during the electric field dependent electron emission, are simulated as a function of temperature. The macroscopic properties (leakage current and..eff) extracted from current-voltage and capacitance-voltage measurements at 20 degrees C are also presented and discussed.

Because of their significant magnetocaloric properties, Ca and Pb-doped LaMnO3 can be employed in magnetic refrigeration systems. The partial substitution effect of Ca2+ by Pb2+ cations on the structural, magnetocaloric properties, and critical behavior of mixed valence perovskites La0.8Ca0.2-xPbxMnO3 (0 <= x <= 0.15), synthesized by the flash combustion route, was studied in this work. The presence of structural transformations of the prepared ceramics from an orthorhombic structure (Pbnm space group) for samples with x <= 0.05 to a rhombohedral system (R (3) over barc space group) for x >= 0.1 was detected by X-ray diffraction analysis, which is related to the A-site disorder. The field-cooled (FC) magnetization indicated a second-order ferromagnetic-paramagnetic transition for the investigated samples when the temperature was increased. Due to the change in the Mn3+/Mn4+ ratio, substituting Ca2+ with larger Pb2+ ions increases the Curie temperature (T-C) by increasing Pb doping content from 90 K for x = 0 to 205 K for x = 0.15. The magnetization isotherms of all samples showing a second-order phase transition were studied, where an applied magnetic field of 5 T, the value of maximum magnetic entropy variation /Delta S-M(max)/ for the sample with x = 0.15 was estimated to be 2.73 Jkg(-1) K-1. In addition, it has a significant relative cooling power of about 276 Jkg(-1) under the same applied magnetic field strength. The critical behavior of the samples was investigated close to T-C. The exponent values were identical to the mean-field method, indicating a large disorder of spin magnetic moments in the perovskite compounds.

In this study, a sol-gel film based on lead sulfide (PbS) quantum dots incorporated into a host network was synthesized as a special nanostructured composite material with potential applications in temperature sensor systems. This work dealt with the optical, structural, and morphological properties of a representative PbS quantum dot (QD)-containing thin film belonging to the Al2O3-SiO2-P2O5 system. The film was prepared using the sol-gel method combined with the spin coating technique, starting from a precursor solution containing a suspension of PbS QDs in toluene with a narrow size distribution and coated on a glass substrate in a multilayer process, followed by annealing of each deposited layer. The size (approximately 10 nm) of the lead sulfide nanocrystallites was validated by XRD and by the quantum confinement effect based on the band gap value and by TEM results. The photoluminescence peak of 1505 nm was very close to that of the precursor PbS QD solution, which demonstrated that the synthesis route of the film preserved the optical emission characteristic of the PbS QDs. The photoluminescence of the lead sulfide QD-containing film in the near infrared domain demonstrates that this material is a promising candidate for future sensing applications in temperature monitoring.

Photocatalysis is one of the approaches for solving environmental issues derived from extremely harmful pollution caused by industrial dyes, medicine, and heavy metals. Titanium dioxide is among the most promising photocatalytic semiconductors; thus, in this work, TiO2 powders were prepared by a hydrothermal synthesis using titanium tetrachloride TiCl4 as a Ti source. The effect of the hydrochloric acid (HCl) concentration on TiO2 formation was analyzed, in which a thorough morpho-structural analysis was performed employing different analysis methods like XRD, Raman spectroscopy, SEM/TEM, and N-2 physisorption. EPR spectroscopy was employed to characterize the paramagnetic defect centers and the photogeneration of reactive oxygen species. Photocatalytic properties were tested by photocatalytic degradation of the rhodamine B (RhB) dye under UV light irradiation and using a solar simulator. The pH value directly influenced the formation of the TiO2 phases; for less acidic conditions, the anatase phase of TiO2 crystallized, with a crystallite size of approximate to 9 nm. Promising results were observed for TiO2, which contained 76% rutile, showing a 96% degradation of RhB under the solar simulator and 91% under UV light after 90 min irradiation, and the best result showed that the sample with 67% of the anatase phase after 60 min irradiation under the solar simulator had a 99% degradation efficiency.

Bulk MgB2 discs were prepared by an in situ route from mixtures of magnesium and boron powders. The boron powders were produced by two methods. The first one consisted of a self-propagating high tem-perature magnesiothermic synthesis (SHS) process followed by acid and fluorine cleaning and a heat treatment in inert atmosphere. This approach produced boron with purities between 86 % and 97 %, where the main impurity was Mg. Depending on the final heat treatment, these boron powders were amorphous or crystalline. In the second route, high purity nano powders (99 %) of boron were obtained by a diborane pyrolysis process. Bulks of MgB2 were characterized by structural, microstructural, and magnetic mea-surements. Critical current density, pinning force aspects and levitation force (including guiding force) details were assessed. Amorphous lower purity boron (86-97 %) obtained by the first processing route was found to promote the largest levitation forces of the MgB2 bulks and, among these samples, the best le-vitation results were recorded when using boron with a purity of 95-97 %. Use of a lower purity boron that decreases the cost of MgB2 promotes large scale production at industrial level of bulk MgB2 super-conducting magnets for levitation applications and enhances the applicability potential of MgB2 super-conductor. The relationship between levitation force and specific features of the samples such as pinning force details are discussed.& COPY; 2023 Elsevier B.V. All rights reserved.

Core/shell nanocomposites based on magnetic magnetite (Fe3O4) and redox-active cerium dioxide (CeO2) nanoparticles (NPs) are promising in the field of biomedical interests because they can combine the ability of magnetic NPs to heat up in an alternating magnetic field (AMF) with the pronounced antioxidant activity of CeO2 NPs. Thus, this report is devoted to Fe3O4/CeO2 nanocomposites (NCPs) synthesized by precipitation of the computed amount of "CeO2-shell" on the surface of prefabricated Fe3O4 NPs. The X-ray diffraction, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy data validated the formation of Fe3O4/CeO2 "core/shell"-like NCPs, in which ultrafine CeO2 NPs with an average size of approximately 3-3.5 nm neatly surround Fe3O4 NPs. The presence of a CeO2 "shell" significantly increased the stability of Fe3O4/CeO2 NCPs in aqueous suspensions: Fe3O4/CeO2 NCPs with "shell thicknesses" of 5 and 7 nm formed highly stable magnetic fluids with zeta-potential values of >+30 mV. The magnetization values of Fe3O4/CeO2 NCPs decreased with a growing CeO2 "shell" around the magnetic NPs; however, the resulting composites retained the ability to heat efficiently in an AMF. The presence of a CeO2 "shell" generates a possibility to precisely regulate tuning of the maximum heating temperature of magnetic NCPs in the 42-50 degrees C range and stabilize it after a certain time of exposure to an AMF by changing the thickness of the "CeO2-shell". A great improvement was observed in both antioxidant and antiamyloidogenic activities. It was found that inhibition of insulin amyloid formation, expressed in IC50 concentration, using NCPs with a "shell thickness" of 7 nm was approximately 10 times lower compared to that of pure CeO2. For these NCPs, more than 2 times higher superoxide dismutase-like activity was observed. The coupling of both Fe3O4 and CeO2 results in higher bioactivity than either of them individually, probably due to a synergistic catalytic mechanism.

Romula (today Resca, Dobrosloveni Village, Romania) was the largest urban and economic center of Dacia Inferior (Malvensis), a Roman province located in the north of the Lower Danube region. In this context, the city market included workshops for the production of ceramic, metal, stone, bone, and glass objects. In 2013, 2015, and 2018, during excavations of the former Roman city, two rectangular glass furnaces were discovered. One has only one chamber, the other has two chambers. A melted glass layer was found on the walls of furnace no. 1, as well as in one room of furnace no. 2. Broken fragments of glass were also found in both. The furnaces are located in the central area of the Roman city. The evidence suggests that the furnaces belong to secondary glass workshops. The glass may have arrived in raw form, where it was remelted and processed. The discovery of these furnaces contributes to the growing body of evidence for Roman glass production around the empire.1