The structural and electronic properties of ReS2 different forms - three-dimensional bulk and two-dimensional monolayer - were studied within density functional theory and pseudopotentials. A method for standardizing the description of bulk unit cells and "artificial" slab unit cells for DFT research has been proposed. The preference of this method for studying zone dispersion has been shown. The influence of the vacuum layer thickness on specified special high-symmetry points is discussed. Electron band dispersion in both classical 3D Brillouin zones and transition to 2D Brillouin zones in the proposed two-dimensional approach using the Niggli form of the unit cell was compared. The proposed two-dimensional approach is preferable for low-symmetry layered crystals such as ReS2. It was established that the bulk ReS2 is a direct gap semiconductor (band gap of 1.20 eV), with the direct transition lying in the X point of the first Brillouin zone, and it is in good agreement with published experimental data. The reduction in material dimension from bulk to monolayer was conducted with an increasing band gap up to 1.45 eV, with a moving direct transition towards the Brillouin zone center. The monolayer of ReS2 is a direct-gap semiconductor in a wide range of temperatures, excluding only a narrow range at low temperatures, where it comes as a quasi-direct gap semiconductor. The transition, situated directly in the Γ-point, lies 3.3 meV below the first direct transition located near this point. The electronic density of states of ReS2 in the bulk and monolayer cases of ReS2 were analyzed. The molecular orbitals were built for both types of ReS2 structures as well as the electron difference density maps. For all types of ReS2 structures, an analysis of populations according to Mulliken and Voronoi was carried out. All calculated data is discussed in the context of weak quantum confinement in the 2D case.
Single crystals of Cu2ZnGeSe4 and Cu2ZnGeS4 solid solutions were developed and successfully obtained using the chemical vapor transfer method, with iodine acting as a transporter. The structure, compositional dependences of lattice parameters, pycnometric and X-ray densities and microhardness were determined. The chemical composition determined by the X-ray microanalysis satisfactorily corresponds to the nominal one with a tolerance of ±5 %. The XRD analysis showed that all the obtained compounds and their solid solutions have unit cell described by tetragonal symmetry. The attice parameters were found to be а = 5.342 ± 0.005 Å, Ñ = 10.51 ± 0.01 Å for the Сu2ZnGeS4 compound and а = 5.607 ± 0.005 Å, Ñ = 11.04 ± 0.01 Å for the Cu2ZnGeSe4, respectively. Structural studies confirmed the validity of the Vegard's law in relation to the obtained samples. The pycnometric densities of â¼4.28 g/cm3 for the Cu2ZnGeS4 and â¼5.46 g/cm3 for the Cu2ZnGeSe4 were found to be slightly less than their X-ray densities of â¼4.32 g/cm3 and â¼5.52 g/cm3, respectively. The maximum microhardness of â¼398 kg/mm2 for these solid solutions corresponds to x = 0.60. The melt point of the solid solutions increases from â¼1180 °C for the Сu2ZnGeSe4 up to â¼1400 °C for the Сu2ZnGeS4. Based on X-ray fluorescence analysis and DTA data, the phase diagram of the Cu2ZnGeSe4-Cu2ZnGeS4 system was constructed. Analysis of the obtained diagram indicates its first type according to Rozbom's classification.
W-Bi2O3 composites were fabricated using the hot isostatic pressing technique for the first time. The duration of the samples sintering was 3 minutes under conditions of high pressure and temperature. The study of microstructural features and chemical composition of sintered samples was carried out using scanning electron microscopy and energy-dispersive X-ray spectroscopy, respectively. The effect of temperature on the quality of the obtained W-Bi2O3 composites is determined. The densest samples were obtained at a pressure of 5 GPa and temperatures of 25 °C and 500 °C, the densities of which were 18.10 and 17.85 g cm-3, respectively. It is presented that high temperature exposure during sintering adversely affects both the composite density and microstructure due to the redox reaction accompanied by the reduction of Bi and the oxidation of W. The results of the W-Bi2O3 structure study using X-ray diffraction analysis showed that all samples included the main bulk-centered cubic W phase. The presence of the WO2 phase is noted only when the sintering temperature is increased up to 850 °C, which is confirmed by the appearance of diffraction peaks that correspond to 111 and 22-2 crystallographic planes. The shielding efficiency of the W-Bi2O3 composite against gamma radiation using the Phy-X/PSD software was evaluated. A Co60 isotope with an energy of 0.826-2.506 MeV was used as a source of gamma radiation. The calculation results were compared with those for Pb and Bi. Key shielding parameters such as the linear attenuation coefficient, half-value layer, tenth-value layer, mean free path, and effective atomic number are determined. The calculation results revealed that the W-Bi2O3 composite surpasses Pb and Bi in its shielding properties, which makes it promising for use as a prospective material for radiation shielding applications.
The polycrystalline SrFe12O19 samples deeply substituted up to at.67% by Al3+, Ga3+, In3+, Co3+, and Cr3+ cations with a high configurational mixing entropy were prepared by solid-phase synthesis. Phase purity and unit cell parameters were obtained from XRD and analyzed versus the average ionic radius of the iron sublattice. The crystallite size varied around â¼4.5 µm. A comprehensive study of the magnetization was realized in various fields and temperatures. The saturation magnetization was calculated using the Law of Approach to Saturation. The accompanying magnetic parameters were determined. The magnetic crystallographic anisotropy coefficient and the anisotropy field were calculated. All investigated magnetization curves turned out to be nonmonotonic. The magnetic ordering and freezing temperatures were extracted from the ZFC and FC curves. The average size of magnetic clusters varied around â¼350 nm. The high values of the configurational mixing entropy and the phenomenon of magnetic dilution were taken into account.
Structural, electronic, elastic and magnetic properties of CeCu3-x Mn x V4O12 (x = 0, 1, 2 and 3) system have been carried out through DFT using GGA, GGA+U and HF potential. The investigation of structural optimization reveals that lattice parameters of the understudy system is reliable with the reported results and are increasing with the Mn substitution due to their greater atomic radii as compare to Cu atom. Both the cohesive energy and the enthalpy show that CeCu3V4O12 is the most thermodynamically stable among these compounds. When Mn is replaced by Cu in these compounds, not only it become semi-metals, but the host compound also changes from non-magnetic to anti-ferromagnetic and their electrical resistance provides further credence to their electronic behavior. Mechanical stability, anisotropy, and ductility are all demonstrated through the elastic characteristics of these compounds. Due to anti-ferromagnetic ductile nature of the Mn base compounds, it is expected that the compounds in the system may use for spintronic application and in magnetic cloaking devices.
This study announces the anomalous phase separation in CoNiP alloy electroplating. The observed phenomenon of the formation of magnetic bubbles was described for the first time for this triple CoNiP system. This study briefly covers all stages of magnetic bubble formation, starting from the formation of an amorphous phosphor-rich sublayer, followed by nucleation centers, and finally cobalt-rich bubbles. An explanation for the anomalous mechanism of bubble formation was found in the effects of additives and the phenomena of depolarization and superpolarization.
The soft/soft (CoFe2O4) x : (Ni0.4Cu0.2Zn0.4Fe2O4) y (CFO x /NCZO y ) nanocomposites (NCs) based on spinel ferrites were produced by the sol-gel method with varying phase's ratio (x : y = 0 : 1; 1 : 1; 2 : 1; 3 : 1; 1 : 3; 1 : 2 and 1 : 0). All NCs consisted of 2 single phases (initial spinels) without any impurities and the absence of chemical interaction between phases. Structural features were investigated and analyzed. The varying of the structural parameters was non-linear and correlated well with the lattice parameter for initial components. There were two maxima observed for all NCs on particle size distribution. It was demonstrated that an increase in the CFO content leads to an increase in the most probable size of the coarse fraction and a decrease in the most probable grain size of the fine fraction. An increase in the NCZO content leads to a decrease in the average size of both fine and coarse fractions. This is obviously due to the large number of defects in the NCZO crystal lattice. The high frequency electromagnetic parameters (real and imaginary parts of the permittivity and permeability, reflection losses) were analyzed in the range of 2-10 GHz. The increase of the energy losses with frequency increase was observed. The nature of the attenuation of the reflected energy associated with the electromagnetic absorption processes due to magnetic losses. Maximal values of the electromagnetic absorption were observed for CFO2/NCZO1 (-18.9 dB). This correlates with the lattice parameters of the composites. The result of the electromagnetic characteristics opens broad perspectives for practical applications such kind of NCs for antenna technology (5G technology) and for electromagnetic absorbing coatings.
This article deals with the effects of current modes on saccharin adsorption during NiFe electrodeposition, and, as a consequence, its effect on chemical composition, crystal structure, and microstructure of deposited films. For this purpose, we obtained NiFe films using direct, pulse, and pulse-reverse electrodeposition modes. The deposit composition, crystal structure, and surface microstructure are studied. Direct current (DC) and pulse current (PC) films have a smooth surface, while a pulse-reverse current (PRC) film surface is covered by a volumetric cauliflower-like microstructure. The mechanism of the film surface development was considered from the point of view of saccharin adsorption and its action as an inhibitor of vertical grain growth during different current modes. During the DC and PC modes, saccharin is freely adsorbed on the growth centers and restrains their vertical growth. Whereas in the case of the PRC electrodeposition, saccharin adsorbs during cathodic pulses and desorbs during anodic pulses. Therefore, its inhibiting action decreases, vertical grain growth rises, and a rougher surface develops.
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.
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.
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.
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 3¯ m) and fcc-Cu (sp. gr. Fm 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.
Multisubstituted barium ferrites with a magnetoplumbite structure were obtained by the method of solid-phase reactions with ferritization and pre-firing. Three-charged, mainly diamagnetic cations Al3+, Cr3+, Ga3+, and In3+ were chosen as substituents for the Fe3+ iron cations, the proportion of which in solid solutions did not exceed 50%. The values of the configurational mixing entropy were calculated for all the compositions. A slight deviation of the chemical composition of the obtained solid solutions from the nominal value was established by the energy-dispersive X-ray spectroscopy method. The phase purity and values of the unit cell parameters were refined from X-ray scattering data using full-profile analysis in the Rietveld method. A non-monotonic behavior of the unit cell parameters as a function of the B-sub-lattice average ionic radius of the magnetoplumbite structure was found. A minimum unit cell volume of ~667.15 Å3 was found for the composition BaFe6.11Al1.56Cr2.17Ga2.16O19 with a B-sub-lattice average ionic radius of ~7.449 Å. The average crystallite size varied within 5.5-6.5 µm. The temperature and field dependencies of the magnetization have been measured. The values of the saturation magnetization, residual magnetization, hysteresis loop squareness, and coercivity at 50 K and 300 K were extracted from the experimental data. Using the Law of Approach to Saturation, the magnetic crystallographic anisotropy coefficient and anisotropy field were calculated. Multisubstitution leads to a significant decrease in such magnetic parameters as the magnetic ordering temperature and spontaneous magnetization at both temperatures. The maximum magnetic ordering temperature of ~297.7 K was found for the composition BaFe5.84Ga6.19O19 with a B-sub-lattice average ionic radius of ~7.586 Å in a field of 500 Oe. A maximum saturation magnetization of ~24.7 emu/g was found for the composition BaFe5.84Ga6.19O19 with a B-sub-lattice average ionic radius of ~7.586 Å at 50 K. A maximum hysteresis loop squareness of ~0.72 was found for the composition BaFe6.11Al1.56Cr2.17Ga2.16O19 with an average ionic radius of ~7.449 Å at 50 K. A maximum magnetic crystallographic anisotropy coefficient of ~2.09 × 105 Erg/g was found for the composition BaFe6.19Al1.25Cr1.57Ga1.74In1.26O19 with a B-sub-lattice average ionic radius of ~7.706 Å at 50 K. The frustrated magnetic state including the nano-sized clusters with an average diameter in the range of 50-200 nm was established from the results of measuring the ZFC and FC temperature magnetizations. The interpretation of the obtained experimental data is carried out taking into account the increased stability of high-entropy phases and regular changes in the intensity of the Fe3+(Al3+, Cr3+, Ga3+, In3+)-O2--Fe3+(Al3+, Cr3+, Ga3+, In3+) indirect superexchange interactions as a result of magnetic dilution of the iron sub-lattice in the magnetoplumbite structure.
The paper discusses the formation of Ta2O5 pillars with Ni tips during thin porous anodic alumina through-mask anodization on Si/SiO2 substrates. The tantalum nanopillars were formed through porous masks in electrolytes of phosphoric and oxalic acid. The Ni tips on the Ta2O5 pillars were formed via vacuum evaporation through the porous mask. The morphology, structure, and magnetic properties at 4.2 and 300 K of the Ta2O5 nanopillars with Ni tips have been studied using scanning electron microscopy, X-ray diffraction, and vibrating sample magnetometry. The main mechanism of the formation of the Ta2O5 pillars during through-mask anodization was revealed. The superparamagnetic behavior of the magnetic hysteresis loop of the Ta2O5 nanopillars with Ni tips was observed. Such nanostructures can be used to develop novel functional nanomaterials for magnetic, electronic, biomedical, and optical nano-scale devices.
Binary and ternary composites (CM) based on M-type hexaferrite (HF), polymer matrix (PVDF) and carbon nanomaterials (quasi-one-dimensional carbon nanotubes-CNT and quasi-two-dimensional carbon nanoflakes-CNF) were prepared and investigated for establishing the impact of the different nanosized carbon on magnetic and electrodynamic properties. The ratio between HF and PVDF in HF + PVDF composite was fixed (85 wt% HF and 15 wt% PVDF). The concentration of CNT and CNF in CM was fixed (5 wt% from total HF + PVDF weight). The phase composition and microstructural features were investigated using XRD and SEM, respectively. It was observed that CM contains single-phase HF, γ- and ß-PVDF and carbon nanomaterials. Thus, we produced composites that consist of mixed different phases (organic insulator matrix-PDVF; functional magnetic fillers-HF and highly electroconductive additives-CNT/CNF) in the required ratio. VSM data demonstrate that the main contribution in main magnetic characteristics belongs to magnetic fillers (HF). The principal difference in magnetic and electrodynamic properties was shown for CNT- and CNF-based composites. That confirms that the shape of nanosized carbon nanomaterials impact on physical properties of the ternary composited-based magnetic fillers in polymer dielectric matrix.
Polymers are often used in medical applications, therefore, some novel polymers and their interactions with photons have been studied. The gamma-ray shielding parameters for Polymethylpentene (PMP), Polybutylene terephthalate (PBT), Polyoxymethylene (POM), Polyvinylidenefluoride (PVDF), and Polychlorotrifluoroethylene (PCTFE) polymers were determined using the Geant4 simulation and discussed in the current work. The mass attenuation coefficients (µ/ρ) were simulated at low and high energies between 0.059 and 1.408 MeV using different radionuclides. The accuracy of the Geant4 simulated results were checked with the XCOM software. The two different methods had good agreement with each other. Exposure buildup factor (EBF) was calculated and discussed in terms of polymers under study and photon energy. Effective atomic number (Zeff) and electron density (Neff) were calculated and analyzed at different energies. Additionally, the half-value layer (HVL) of the polymers was evaluated, and the results of this parameter showed that PCTFE had the highest probability of interaction with gamma photons compared to those of the other tested polymers.
High-quality and compact arrays of Ni nanowires with a high ratio (up to 700) were obtained by DC electrochemical deposition into porous anodic alumina membranes with a distance between pores equal to 105 nm. The nanowire arrays were examined using scanning electron microscopy, X-ray diffraction analysis and vibration magnetometry at 300 K and 4.2 K. Microscopic and X-ray diffraction results showed that Ni nanowires are homogeneous, with smooth walls and mostly single-crystalline materials with a 220-oriented growth direction. The magnetic properties of the samples (coercivity and squareness) depend more on the length of the nanowires and the packing factor (the volume fraction of the nanowires in the membrane). It is shown that the dipolar interaction changes the demagnetizing field during a reversal magnetization of the Ni nanowires, and the general effective field of magnetostatic uniaxial shape anisotropy. The effect of magnetostatic interaction between ultra-long nanowires (with an aspect ratio of >500) in samples with a packing factor of ≥37% leads to a reversal magnetization state, in which a "curling"-type model of nanowire behavior is realized.
The gamma radiation shielding ability for CaO-K2O-Na2O-P2O5 glasses were experimentally determined between 0.0595 and 1.41 MeV. The experimental MAC results were compared with theoretical results obtained from the XCOM software to test the accuracy of the experimental values. Additionally, the effect of increasing the P2O5 in the glass composition, or reducing the Na2O content, was evaluated at varying energies. For the fabricated glasses, the experimental data strongly agreed with the XCOM results. The effective atomic number (Zeff) of the fabricated glasses was also determined. The Zeff values start out at their maximum (12.41-12.55) at the lowest tested energy, 0.0595 MeV, and decrease to 10.69-10.80 at 0.245 MeV. As energy further increases, the Zeff values remain almost constant between 0.344 and 1.41 MeV. The mean free path (MFP) of the fabricated glasses is investigated and we found that the lowest MFP value occurs at the lowest tested energy, 0.0595 MeV, and lies within the range of 1.382-1.486 cm, while the greatest MFP can be found at the highest tested energy, 1.41 MeV, within the range of 8.121-8.656 cm. At all energies, the KCNP40 sample has the lowest MFP, while the KCNP60 sample has the greatest. The half value layer (HVL) for the KCNP-X glasses is determined. For all the selected energies, the HVL values follow the order of KCNP40 < KCNP45 < KCNP50 < KCNP55 < KCNP60. The HVL of the KCNP50 sample increased from 0.996 to 2.663, 3.392, 4.351, and 5.169 cm for energies of 0.0595, 0.245, 0.444, 0.779, and 1.11 MeV, respectively. The radiation protection efficiency (RPE) results reveal that decreasing the P2O5 content in the glasses improves the radiation shielding ability of the samples. Thus, the KCNP40 sample has the best potential for photon attenuation applications.
The effect of microstructure on the efficiency of shielding or shunting of the magnetic flux by permalloy shields was investigated in the present work. For this purpose, the FeNi shielding coatings with different grain structures were obtained using stationary and pulsed electrodeposition. The coatings' composition, crystal structure, surface microstructure, magnetic domain structure, and shielding efficiency were studied. It has been shown that coatings with 0.2-0.6 µm grains have a disordered domain structure. Consequently, a higher value of the shielding efficiency was achieved, but the working range was too limited. The reason for this is probably the hindered movement of the domain boundaries. Samples with nanosized grains have an ordered two-domain magnetic structure with a permissible partial transition to a superparamagnetic state in regions with a grain size of less than 100 nm. The ordered magnetic structure, the small size of the domain, and the coexistence of ferromagnetic and superparamagnetic regions, although they reduce the maximum value of the shielding efficiency, significantly expand the working range in the nanostructured permalloy shielding coatings. As a result, a dependence between the grain and domain structure and the efficiency of magnetostatic shielding was found.
The densely packed arrays of Ni nanowires of 70 nm diameter and 6-12 µm length were obtained via electrodeposition into porous alumina membranes (PAAMs) of 55-75 µm thickness. The morphology, microstructure and magnetic properties between the room and liquid-helium temperature of Ni nanowires in PAAMs have been investigated using scanning electron microscopy, X-ray diffraction and vibrating sample magnetometry. The crystal structure of the Ni nanowires is fcc with (220) preferred orientation. The magnetic characteristics of the Ni nanowires in PAAMs were compared with the same characteristics of bulk Ni and with other researchers' data. The effect of the porous alumina membrane and the Ni nanowires synthesis conditions on the magnetic characteristics of Ni nanowire arrays has been studied. The coercivity reached more than 750 kOe and the squareness ratio up to 0.65 under the proposed optimal synthesis conditions for Ni nanowires. Magnetic parameters of the densely packed arrays of Ni nanowires allow using them in magnetic recording media, hard disk drives, storage systems and sensors. In addition, such structures are of considerable interest for basic research on nanomagnetism which is significantly different from the magnetic properties of bulk and thin films materials.
