National Institute Of Materials Physics - Romania

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5507 articles found

121. New superdielectric materials: (1-x) SrFe12O19 - x BNT-BT nanocomposites

Authors: Greculeasa, SG; Comanescu, C; Iacob, N; Kuncser, A; Smaranda, I; Amarande, L; Cioangher, M; Burdusel, M; Teodorescu, V

Published: OCT 1 2022, PHYSICA B-CONDENSED MATTER, 642, 414139, DOI: 10.1016/j.physb.2022.414139

Novel (1-x) SrFe12O19 - x BNT-BT0.08 (x = 0; 0.5; 0.8; 1) nanocomposites were explored in this study. The samples were produced by sol-gel method and compacted by conventional sintering. The composition, morphology, local structure, dielectric and magnetic properties were investigated by X-ray diffraction, Transmission Electron Microscopy, Impedance Analysis, Mossbauer spectroscopy, and SQUID magnetometry. The desired composition and the presence of the magnetoplumbite SrFe12O19 and perovskite BNT-BT structures were verified by X-ray diffraction. Irregular morphology and large size distributions are evidenced in the electron microscopy micrographs. The reported room temperature dielectric constants in this study are the highest values obtained in multiferroic composites at room temperature: giant dielectric constants (similar to 1.3 x 10(6)) were obtained, relative to 0.13 x 10(4) in BNT-BT. The hyperfine parameters allowed the identification of the Wyckoff positions of the Fe ions corresponding closely to the theoretical case. The hard magnetic character of the SrFe12O19 phase is evidenced from the magnetic measurements. For the first time in multifermic composites, superdielectric characteristics are evidenced at room temperature.

122. Influence of relative humidity on CO2 interaction mechanism for Gd-doped SnO2 with respect to pure SnO2 and Gd2O3

Authors: Ghica, C; Mihalcea, CG; Simion, CE; Vlaicu, ID; Ghica, D; Dinu, IV; Florea, OG; Stanoiu, A

Published: OCT 1 2022, SENSORS AND ACTUATORS B-CHEMICAL, 368, 132130, DOI: 10.1016/j.snb.2022.132130

The paper aims to identify the CO2 interaction mechanism for chemical sensors based on Gd-doped SnO2, SnO2 and Gd2O3 powders deposited as thick sensitive layers. The low reactivity of CO2 conferred by the thermodynamic stability and chemical inertia can be offset by the presence of relative humidity. The sensitive powders were prepared by wet chemical co-precipitation method. The Gd concentration was varied from 1% to 20 at% in order to determine the limit for Gd integration as a doping ion prior to chemical segregation as a secondary phase. Analytical transmission electron microscopy points to a homogeneous Gd doping of the nanostructured SnO2 powders for low doping concentrations and the formation of a nanocomposite based on SnO2 as main phase and cubic Gd2O3 as secondary phase for the highly doped samples. The electrical resistance is either influenced by the density of oxygen vacancies, or is the result of compensation for two opposite behaviours into the SnO2- Gd2O3 nanocomposite structures. The CO2 exposure to humid atmosphere determines distinct behaviours cor-responding to SnO2 and Gd2O3 as constitutive elements. The associated CO2 interaction mechanism is based on simultaneous DC electrical resistance and Contact Potential Difference measurements, which allow decoupling the ionosorption from the dipolar processes, thus highlighting specific chemical interactions on the SnO2 and Gd2O3 surfaces.

123. Chemical sensing and actuation properties of polypyrrole coated fibers

Authors: Beregoi, M; Beaumont, S; Jinga, SI; Otero, TF; Enculescu, I

Published: OCT 1 2022, SMART MATERIALS AND STRUCTURES, 31, 105012, DOI: 10.1088/1361-665X/ac83ff

Designing complex electrochemical artificial muscles aims towards novel devices which besides excellent actuation capabilities should also present the ability to self-sense the modification of environmental parameters. In order to improve efficiency, mimicking the structure of natural muscles, synthetic actuators should have a similar fibrillary morphology. The importance of using materials based on fiber building blocks in actuators aimed at soft robotics field was demonstrated in the present report by comparing a fibrillary artificial muscle with one based on a classical film structure. Nylon electrospun fiber meshes and films were covered in the same conditions with a thin polypyrrole (PPy) layer. The fibrillary electrospun web morphology mimics that of natural muscles and the structure performs a fast, ample bending movement in liquid electrolyte when switching an applied electric potential between -0.6 and +0.6 V. Using the same actuation conditions, no movement of a film based artificial muscle was observed. In order to check the sensing ability of both fibrillary and film like electroactive architectures, their response i.e. PPy reaction when potential cycles were applied in different concentrations of LiClO4 electrolyte were recorded. The obtained results suggest that the ion exchange of the fibrillary artificial muscle is more efficient due to its higher active surface and such devices could work also as dual device (sensor/artificial muscle).

124. Influence of erbium doping on the structural, magnetic and optical properties of hematite (?-Fe(2)O( )3) nanorods

Authors: Popov, N; Ristic, M; Kuncser, V; Zadro, K; Velinov, N; Badica, P; Alexandru-Dinu, A; Iacob, N; Krehula, LK; Music, S; Krehula, S

Published: OCT 2022, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 169, 110857, DOI: 10.1016/j.jpcs.2022.110857

Pure and Er-doped hematite (alpha-Fe2O3) nanorods were prepared by a two-step method involving hydrothermal synthesis and calcination of pure and Er-doped goethite (alpha-FeOOH) nanorods. Substitution of Fe3+ by Er3+ in the crystal structure of hematite caused morpho-structural changes such as expansion of the unit cell and gradual shortening and rounding of hematite nanorods towards formation of nanoellipsoids. These changes induced modification of magnetic and optical properties suggesting the possibility of a systematic control of physical properties via rare earth substitution. A decrease in the hyperfine magnetic field, coercive field and Morin transition temperature, as well as an increase of the magnetic susceptibility and a narrowing of the optical band gap were observed by substitution. Intimate mechanisms related to the formation of more and more defect-like hematite phases with decreased temperatures for the transition to the low temperature antiferromagnetic phase at increased doping level were evidenced via temperature dependent Mo center dot ssbauer spectroscopy.

125. Tuning the acidity by addition of transition metal to Mn modified hollow silica spheres and their catalytic activity in ethanol dehydration to ethylene

Authors: Florea, M; Bocirnea, A; Neatu, S; Kuncser, AM; Trandafir, MM; Neatu, F

Published: SEP 25 2022, APPLIED CATALYSIS A-GENERAL, 646, 118860, DOI: 10.1016/j.apcata.2022.118860

Due to the currently worldwide petrochemical feedstock shortage, the ethylene synthesis from renewable non-oil sources becomes of high interest. The catalysts were prepared in two steps: (i) formation of spheres containing the carbon-coated Mn core by hydrothermal method, (ii) formation of the Si-Zr oxide shell by sol-gel method. The prepared catalysts were characterized by N2 physisorption, SEM-EDX, XRD, XPS, and NH3-TPD. The catalytic results have shown that Fe, Zn or Ni modified Mn core exhibited superior activity compared to the catalysts containing only Mn in the core. With 75% yield and 98% ethanol conversion at 350 degrees C and WHSV of 1.4 h-1, MnNi@SiZr was the best catalyst. These results are due to an increased number of acid sites compared to the other materials and an optimal ratio of weak/medium acid sites. Our findings suggest new lines for developing active and stable catalysts for ethylene synthesis from ethanol.

126. Charge transport mechanisms in free-standing devices with electrospun electrodes

Authors: Ciobotaru, IC; Polosan, S; Enculescu, M; Nitescu, A; Enculescu, I; Beregoi, M; Ciobotaru, CC

Published: SEP 24 2022, NANOTECHNOLOGY, 33, 395203, DOI: 10.1088/1361-6528/ac7ac1

Embedding electronic and optoelectronic devices in common, daily use objects is a fast developing field of research. New architectures are needed for migrating from the classic wafer- based substrates. Novel types of flexible PMMA/Au/Alq(3)/LiF/Al structures were obtained starting from electrospun polymer fibers. Thus, using an electrospinning process poly (methyl metacrylate) (PMMA) nanofibers were fabricated. A thin Au layer deposition rendered the fiber array conductive, this being further employed as the anode. The next steps consisted of the thermal evaporation of tris(8-hydroxyquinolinato) aluminum (Alq(3)) and aluminum deposition as the cathode. The Au covered PMMA nanofiber layer had a similar behavior with an indium tin oxide film i.e. low sheet resistance 10.6 omega/sq and high transparency. The low electrode resistivities allow an electron drift mobility of about 10(-6) cm(2) V-1 s(-1) at a low applied field, similar to the counterpart structures based on thin films. Concerning the relaxation processes in these structures, the Cole-Cole plots exhibit a slightly deformed semicircle, indicating a more complex equivalent circuit for the processes between metal electrodes and the active layer. This equivalent circuit includes reactance equivalent processes at the anode, cathode, in the active layer and most probably originates from the roughness of the metallic electrodes.

127. BaTiO3 nanocubes-Gelatin composites for piezoelectric harvesting: Modeling and experimental study

Authors: Ciomaga, CE; Horchidan, N; Padurariu, L; Stirbu, RS; Tiron, V; Tufescu, FM; Topala, I; Condurache, O; Botea, M; Pintilie, I; Pintilie, L; Rotaru, A; Caruntu, G; Mitoseriu, L

Published: SEP 15 2022, CERAMICS INTERNATIONAL, 48, DOI: 10.1016/j.ceramint.2022.05.264

Flexible composites containing BaTiO3 nanoparticles into Gelatin bio-polymer matrix were designed and investigated. Following the idea that the electric field concentration in corners/edges at the interfaces between dissimilar materials give rise to enhanced effective permittivity in composites, cuboid-like BaTiO3 nanoparticles have been employed as nanofillers into Gelatin matrix by using an inexpensive solution-based processing method. As predicted by finite element method simulations developed for cubic-like inclusions into a homogeneous polymer matrix, the experimental permittivity of xBT-(1-x)Gelatin composites increases when increasing the high-permittivity filler addition. For the composition x = 40 wt% (corresponding to 12 vol% BaTiO3 addition), permittivity reaches epsilon r -15.7 with respect to epsilon r -9.8 of pure Gelatine (measured at 105 Hz), while the average piezoelectric coefficient d33 as determined by piezoelectric force microscopy shows a remarkable increase up to 21 pm/V in composites with x = 40 wt%, in comparison to -7 pm/V in pure Gelatin. By using the experimentally determined material constants, the simulated piezoelectric voltage output vs. time has shown a similar increase (about a doubling of its amplitude) of the harvesting signal in the composite with x = 40 wt% BT, with respect to one of the polymer matrix, thus demonstrating the beneficial role of embedding BT nanoparticles into the biopolymer for increasing the mechanical harvesting response.

128. Electrochemical characterization of shikonin and in-situ evaluation of interaction with DNA

Authors: Leote, RJB; Sanz, CG; Diculescu, VC

Published: SEP 15 2022, JOURNAL OF ELECTROANALYTICAL CHEMISTRY, 921, 116663, DOI: 10.1016/j.jelechem.2022.116663

Shikonin, a natural compound with pharmaceutical properties, has attracted interest due to its anti-oxidant properties, potential anti-cancer activity and activity over several biological pathways, such as dsDNA transcription/replication of cancer cells and inhibition of pyruvate kinase M2. The electrochemical behavior of shikonin in aqueous media was investigated at glassy carbon electrodes by cyclic and differential pulse voltammetry. The reduction involves the quinone moiety and formation of a semiquinone intermediate. In the absence of dissolved oxygen, the reduction is reversible while in normal atmosphere leads to formation of superoxide cation. The oxidation occurs at the dihydroxy moiety and reversibility was only observed in acid electrolytes. A redox mechanism was proposed. The interaction between shikonin and dsDNA was evaluated in incubated solutions and in situ with the dsDNA-electrochemical biosensor. The mechanism of interaction is time-dependent and follows an initial binding step at the grooves of the double strand leading to conformational modifications recognized through the variation of guanine and adenine oxidation peaks. The in-situ electrochemical production of the semiquinone intermediate leads to a preferential interaction with guanine residues, promoting their oxidation and consequently occurrence 8-oxo-guanine. An interaction mechanism was proposed.

129. Enhanced photoelectrochemical activity of WO3-decorated native titania films by mild laser treatment

Authors: Spataru, T; Mihai, MA; Preda, L; Marcu, M; Radu, MM; Becherescu, ND; Velea, A; Zaki, MY; Udrea, R; Satulu, V; Spataru, N

Published: SEP 15 2022, APPLIED SURFACE SCIENCE, 596, 153682, DOI: 10.1016/j.apsusc.2022.153682

The effectiveness of the electrochemical WO3-modification as a method for improving the photoactivity of native air-formed TiO2 layers was assessed. The way in which a mild laser treatment influences the photo-electrochemical performances of the thus obtained WO3/TiO2 systems was also investigated. At laser-treated electrodes (L-WO3/TiO2), the melting-solidification process induced by the treatment led to a smaller size of the deposited WO3 particles and to their better dispersion on the surface. The treatment also enhanced the surface oxygen deficiency and ensured better relative absorptivity of the oxygenated species on the surface. These features, together with the intrinsic narrower bandgap of the WO3/TiO2 composites, the higher donor density and the lower flat band potential of L-WO3/TiO2 enabled faster kinetic of the oxygen photoanodic evolution. Importantly, the same process exhibited a cathodic shift of its onset potential. The laser treatment also strongly enhanced the photoelectrocatalytic performances for UV-assisted methanol anodic oxidation.

130. Bioinspired polypyrrole based fibrillary artificial muscle with actuation and intrinsic sensing capabilities

Authors: Beregoi, M; Beaumont, S; Evanghelidis, A; Otero, TF; Enculescu, I

Published: SEP 2 2022, SCIENTIFIC REPORTS, 12, 15019, DOI: 10.1038/s41598-022-18955-6

A non-conventional, bioinspired device based on polypyrrole coated electrospun fibrous microstructures, which simultaneously works as artificial muscle and mechanical sensor is reported. Fibrous morphology is preferred due to its high active surface which can improve the actuation/sensing properties, its preparation still being challenging. Thus, a simple fabrication algorithm based on electrospinning, sputtering deposition and electrochemical polymerization produced electroactive aligned ribbon meshes with analogous characteristics as natural muscle fibers. These can simultaneously generate a movement (by applying an electric current/potential) and sense the effort of holding weights (by measuring the potential/current while holding objects up to 21.1 mg). Electroactivity was consisting in a fast bending/curling motion, depending on the fiber strip width. The amplitude of the movement decreases by increasing the load, a behavior similar with natural muscles. Moreover, when different weights were hung on the device, it senses the load modification, demonstrating a sensitivity of about 7 mV/mg for oxidation and - 4 mV/mg for reduction. These results are important since simultaneous actuation and sensitivity are essential for complex activity. Such devices with multiple functionalities can open new possibilities of applications as e.g. smart prosthesis or lifelike robots.