Search Results (38)

Hybrid dysprosium-doped borate glassy samples [B-Gly/Dy]^HDG (Borate Glass/Dysprosium)^{Hybrid Doped Glass} were prepared in this study via the melt-quenching method. Its linear/nonlinear optical, photoluminescence, hardness indentation, and micro-creep properties were analyzed. The amorphous structure for all the prepared samples was confirmed from the XRD patterns. In addition, density functional theory (DFT), optimized by TD-DFT and Crystal Sleuth, was used to study the structure and crystallinity of the [B-Gly/Dy]^HDG as isolated molecules and agreed with the peaks of experimental XRD patterns. Additionally, theoretical lattice types were studied using Polymorph, a content studio software, and orthorhombic Pc21b (29) and triclinic P-1 (2) structures were provided. Both mechanical and optical properties were responses to different concentrations of Dy₂O₃ in the glassy borate system. It was found that the length of indentation increases by increasing the load time, and the hardness decreases by increasing the load time. The stress exponent value also increased from 4.1 to 6.3. The indentation strain increases by increasing the load time. The direct optical band gap was evaluated using the Davis–Mott relation. Urbach energy and its connection to the disorder degree in materials were studied depending on the Dy₂O₃ concentration. The acquired optical parameters were also analyzed to determine the nonlinear refractive index as well as the linear and third-order nonlinear optical susceptibility of the investigated glass samples. The photoluminescence emission spectra were recorded, and their attributed transitions were studied. The mechanical studies showed that the hardness values increased by increasing Dy₂O₃ concentrations from 4160.54 to 5631.58 Mpa. The stress exponent value also increased from 4.1 to 6.3. Therefore, the higher value of stress exponent (S) is more resistant to indentation creep. Full article

The current research is focused on the chemical process and characterization of Co-based Y-type hexaferrite, electrochemically active polypyrrole doped with dodecylbenzene sulphonicacid (PPy-DBSA) and their composites. The microemulsion technique was used to produce hexaferrite with the formula Sr₂Co₂Fe₁₂O₂₂. The resistivity of pure ferrite specimens was 103 ohm-cm, which was lower than the 106 ohm-cm resistivity of the monomer utilized in the polymerization operation. As the temperature increases, the DC resistance decreases, revealing the specimens’ semiconductor nature. The cole-cole plots have been used to assess whether significant grain boundaries were involved in the dielectric relaxation process. By increasing the frequency, the electrochemical performance of all specimens was enhanced. Using the rate equation, ionic conductivity demonstrates that polarons are responsible for conduction. Because of the characteristics of the polymer PPY-conducting DBSA, the composites PPY/DBSA + Sr₂Co₂Fe₁₂O₂₂ exhibit a higher dielectric loss of 35 at 1 MHz. This specimen is perfect for electrical radiation shielding (EMI).These ferrites are widely used as permanent magnets, in microwave devices, high-density perpendicular media, and rigid disk media without lubricant and protective layers. Full article

The structural, electrical, and magneto-elastic properties of lanthanide base nitride (Ln = Dy-Lu) anti-perovskites were investigated using density functional theory (DFT). The reported structural outcomes are consistent with the experiment and decrease from Dy to Lu due to the decrease ofatomic radii of Ln atoms. According to the electronic band profile, the metallic characteristics of these compounds are due to the crossing over of Ln-f states at the Fermi level and are also supported by electrical resistivity. The resistivity of these compounds at room temperature demonstrates that they are good conductors. Their mechanical stability, anisotropic, load-bearing, and malleable nature are demonstrated by their elastic properties. Due to their metallic and load-bearing nature, in addition to their ductility, these materials are suitable as active biomaterials, especially when significant acting loads are anticipated, such as those experienced by such heavily loaded implants as hip and knee endo-prostheses, plates, screws, nails, dental implants, etc. In thesecases, appropriate bending fatigue strength is required in structural materials for skeletal reconstruction. Magnetic properties show that all compounds are G-type anti-ferromagnetic, with the Neel temperatures ranging from 24 to 48 K, except Lu₃Nin, which is non-magnetic. Due to their anti-ferromagnetic structure, magnetic probes cannot read data contained in anti-ferromagnetic moments, therefore, data will be unchanged by disrupted magnetic field. As a result, these compounds can be the best candidates for magnetic cloaking devices. Full article

Nanostructured aluminum, tantalum, and vanadium oxide layers on glass substrates were obtained by electrochemical anodizing in oxalic and sulfuric–oxalic electrolytes. The morphological and optical properties of the obtained structures were investigated experimentally by scanning electron microscopy and transmission spectroscopy. Obtained oxide coatings are quasi-ordered arrays of vertical (aluminum oxide/tantalum oxide, aluminum oxide/vanadium oxide, and aluminum oxide obtained in the oxalic electrolyte) or non-ordered tree-like (aluminum oxide obtained in the sulfuric–oxalic electrolyte) pores depending on the initial film metal and anodizing technology. The light transmission in the range of 750–1200 nm is up to 60% for aluminum oxide/tantalum oxide/glass (annealed) and quasi-ordered aluminum oxide/glass structures, and around 40% for aluminum oxide/tantalum oxide/glass (not annealed) and aluminum oxide/vanadium oxide. Non-ordered aluminum oxide is characterized by low transmission (no more than 8%) but has a developed surface and may be of interest for the formation of films with poor adhesion on smooth substrates, for example, photocatalytic active xerogels. The refractive indices of dispersion of the obtained layers were calculated from the transmission spectra by the envelope method. The dispersion of the refractive indices of the obtained oxide films is insignificant in a wide range of wavelengths, and the deviation from the average value is assumed to be observed near the intrinsic absorption edges of the films. The glasses with proposed semi-transparent nanostructured oxide layers are promising substrate structures for subsequent sol–gel coating layers used in photocatalytic purification systems or up-conversion modules of tandem silica solar cells with forward and reverse illumination. Full article

In this study, SrFe_12-xNd_xO₁₉, where x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5, was prepared using high-energy ball milling. The prepared samples were characterized by X-ray diffraction (XRD). Using the XRD results, a comparative analysis of crystallite sizes of the prepared powders was carried out by different methods (models) such as the Scherrer, Williamson–Hall (W–H), Halder–Wagner (H–W), and size-strain plot (SSP) method. All the studied methods prove that the average nanocrystallite size of the prepared samples increases by increasing the Nd concentration. The H–W and SSP methods are more accurate than the Scherer or W–H methods, suggesting that these methods are more suitable for analyzing the XRD spectra obtained in this study. The specific saturation magnetization (σ_s), the effective anisotropy constant (K_eff), the field of magnetocrystalline anisotropy (H_a), and the field of shape anisotropy (H_d) for SrFe_12-xNd_xO₁₉ (0 ≤ x ≤ 0.5) powders were calculated. The coercivity (H_c) increases (about 9% at x = 0.4) with an increasing degree of substitution of Fe³⁺ by Nd^3+, which is one of the main parameters for manufacturing permanent magnets. Full article

To increase the attractiveness of the practical application of molecular sensing methods, the experimental search for the optimal shape of silver nanostructures allowing to increase the Raman cross section by several orders of magnitude is of great interest. This paper presents a detailed study of spatially separated plasmon-active silver nanostructures grown in SiO₂/Si template pores with crystallite, dendrite, and “sunflower-like” nanostructures shapes. Nile blue and 2-mercaptobenzothiazole were chosen as the model analytes for comparative evaluation of the Raman signal amplification efficiency using these structures. It was discussed the features of the structures for the enhancement of Raman intensity. Finally, we showed that silver crystals, dendrites, and “sunflower-like” nanostructures in SiO₂/Si template could be used as the relevant materials for Raman signal amplification, but with different efficiency. Full article

NiFe films with a composition gradient are of particular interest from the point of view of fundamental science and practical applications. Such gradient magnetic structures may exhibit unique functional properties useful for sensory applications and beyond. The issue surrounds the anomaly concerning the compositional gradient formed near the substrate in electrolytically deposited binary and ternary iron-containing alloys, which has not previously been clearly explained. In this work, light is shed on this issue, and a clear relationship is found between the structure and surface properties of the substrate, the initially formed NiFe layers and the film composition gradient. Full article

Co-Ni ferrite is one of the crucial materials for the electronic industry. A partial substitution with a rare-earth metal brings about modification in crystal lattice and broadens knowledge in the discovery of new magnetic material. Current work reports a Ga³⁺ substitution in the Co-Ni ferrite with composition Co_0.5Ni_0.5Fe_2−xGa_xO₄ (where x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0), herein referred to as spinel ferrite microspheres (CoNiGa-SFMCs). The samples were crystallized hydrothermally showing a hollow sphere morphology. The crystal phase, magnetic, morphology, and optical behaviour were examined using various microscopy and spectroscopic tools. While the XRD confirmed the phase of SFMCs, the crystallite size varied between 9 and 12 nm. The Tauc plot obtained from DRS (diffuse reflectance spectroscopy) shows the direct optical energy bandgap (E_g) of the products, with the pristine reading having the value of 1.41 eV E_g; the band gap increased almost linearly up to 1.62 eV along with rising the Ga³⁺ amount. The magnetic features, on the other hand, indicated the decrease in coercivity (H_c) as more Ga³⁺ is introduced. Moreover, there was a gradual increase in both saturation magnetization (M_s) and magnetic moment ($n_B$) with increasing amount of Ga³⁺ till x = 0.6 and then a progressive decline with increases in the x content; this was ascribed to the spin-glass-like behavior at low temperatures. It was detected that magnetic properties correlate well with crystallite/particle size, cation distribution, and anisotropy. Full article

Today, an actual task of photovoltaics is the search for new light-absorbing materials for solar cells, which will make them more efficient and economically affordable. Semiconductor Cu₂NiSn(S,Se)₄ (CNTSSe) thin films are promising materials due to suitable optical and electrical properties. This compound consists of abundant, inexpensive, and low-toxicity elements. However, few results of studying the properties of CNTSSe films have been presented in the literature. This paper presents the results of studying the morphology, phase composition, and crystal structure of the CNTSSe films, which were first obtained by high-temperature annealing of electrodeposited Ni/Cu/Sn/Ni precursors on glass/Mo substrates in chalcogen vapor. The films were studied using X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. It has been found that sequential electrochemical deposition makes it possible to obtain the Ni/Cu/Sn/Ni precursors of the required quality for further synthesis of the films. It is shown that high-temperature annealing in chalcogen vapor in air makes it possible to synthesize stable polycrystalline CNTSSe films. The obtained results confirm that the production of CNTSSe films is suitable for use in solar cells by the proposed method, which can be improved by more precise control of the precursor composition and annealing conditions. Full article

The compound BiFe_0.7Mn_0.3O₃ consisting at room temperature of coexistent anti-polar orthorhombic and polar rhombohedral phases has a metastable structural state, which has been studied by laboratory X-ray, synchrotron and neutron diffraction, magnetometry, differential thermal analysis, and differential scanning calorimetry. Thermal annealing of the sample at temperatures above the temperature-driven phase transition into the single phase rhombohedral structure (~700 K) causes an increase of the volume fraction of the rhombohedral phase at room temperature from ~10% up to ~30%, which is accompanied by the modification of the magnetic state, leading to strengthening of a ferromagnetic component. A strong external magnetic field (~5 T) applied to the sample notably changes its magnetic properties, as well as provides a reinforcement of the ferromagnetic component, thus leading to an interaction between two magnetic subsystems formed by the antiferromagnetic matrix with non-collinear alignment of magnetic moments and the nanoscale ferromagnetic clusters coexisting within it. The modification of the structural state and magnetic properties of the compounds and a correlation between different structural and magnetic phases are discussed focusing on the effect of thermal annealing and the impact of an external magnetic field. Full article

In the presented work, B₄C was irradiated with xenon swift heavy ions at the energy of 167 MeV. The irradiation of the substrate was done at room temperature to a fluence of 3.83 × 10¹⁴ ion/cm². The samples were then analyzed with the X-ray diffraction technique to study the structural modification, as it can probe the region of penetration of xenon atoms due to the low atomic number of the two elements involved in the material under study. The nano-cluster formation under ion irradiation was observed. Positron lifetime (PLT) calculations of the secondary point defects forming nanoclusters and introduced into the B₄C substrate by hydrogen and helium implantation were also carried out with the Multigrid instead of the K-spAce (MIKA) simulation package. The X-ray diffraction results confirmed that the sample was B₄C and it had a rhombohedral crystal structure. The X-ray diffraction indicated an increase in the lattice parameter due to the Swift heavy ion (SHI) irradiation. In B₁₂-CCC, the difference between τ with the saturation of H or He in the defect is nearly 20 ps. Under the same conditions with B₁₁C-CBC, there is approximately twice the value for the same deviation. Full article

The results of studies on the wettability properties and preparation of porous anodic alumina (PAA) membranes with a 3.3 ± 0.2 μm thickness and a variety of pore sizes are presented in this article. The wettability feature results, as well as the fabrication processing characteristics and morphology, are presented. The microstructure effect of these surfaces on wettability properties is analyzed in comparison to outer PAA surfaces. The interfacial contact angle was measured for amorphous PAA membranes as-fabricated and after a modification technique (pore widening), with pore sizes ranging from 20 to 130 nm. Different surface morphologies of such alumina can be obtained by adjusting synthesis conditions, which allows the surface properties to change from hydrophilic (contact angle is approximately 13°) to hydrophobic (contact angle is 100°). This research could propose a new method for designing functional surfaces with tunable wettability. The potential applications of ordinary alumina as multifunctional films are demonstrated. Full article

Oxygen and hydrogen generated by water electrolysis may be utilized as a clean chemical fuel with high gravimetric energy density and energy conversion efficiency. The hydrogen fuel will be the alternative to traditional fossil fuels in the future, which are near to exhaustion and cause pollution. In the present study, flowery-shaped In₂MnSe₄ nanoelectrocatalyst is fabricated by anion exchange reaction directly grown on nickel foam (NF) in 1.0 M KOH medium for oxygen evolution reaction (OER). The physiochemical and electrical characterization techniques are used to investigate the chemical structure, morphology, and electrical properties of the In₂MnSe₄ material. The electrochemical result indicates that synthesized material exhibits a smaller value of Tafel slope (86 mV/dec), lower overpotential (259 mV), and high stability for 37 h with small deterioration in the current density for a long time. Hence, the fabricated material responds with an extraordinary performance for the OER process and for many other applications in the future. Full article

Nanocomposite films based on spinel ferrite (Mg_0.8Zn_0.2Fe_1.5Al_0.5O₄) in a PVA matrix were obtained. An increase in the spinel concentration to 10 wt.% caused an avalanche-like rise in roughness due to the formation of nanoparticle agglomerates. The lateral mode of atomic force microscopy (AFM) allowed us to trace the agglomeration dynamics. An unexpected result was that the composite with 6 wt.% of filler had a low friction coefficient in comparison with similar composites due to the successfully combined effects of low roughness and surface energy. The friction coefficient decreased to 0.07 when the friction coefficient of pure PVA was 0.72. A specially developed method for measuring nano-objects’ surface energy using AFM made it possible to explain the anomalous nature of the change in tribological characteristics. Full article

The W–Cu composites with nanosized grain boundaries and high effective density were fabricated using a new fast isostatic hot pressing method. A significantly faster method was proposed for the formation of W–Cu composites in comparison to the traditional ones. The influence of both the high temperature and pressure conditions on the microstructure, structure, chemical composition, and density values were observed. It has been shown that W–Cu samples have a polycrystalline well-packed microstructure. The copper performs the function of a matrix that surrounds the tungsten grains. The W–Cu composites have mixed bcc-W (sp. gr. Im $\overline{3}$ m) and fcc-Cu (sp. gr. Fm $\overline{3}$ m) phases. The W crystallite sizes vary from 107 to 175 nm depending on the sintering conditions. The optimal sintering regimes of the W–Cu composites with the highest density value of 16.37 g/cm³ were determined. Tungsten–copper composites with thicknesses of 0.06–0.27 cm have been fabricated for the radiation protection efficiency investigation against gamma rays. It has been shown that W–Cu samples have a high shielding efficiency from gamma radiation in the 0.276–1.25 MeV range of energies, which makes them excellent candidates as materials for radiation protection. Full article