This study presents the dielectric properties of a barium titanate–gadolinium ferrite composite material, obtained through a solid-state reaction method. The aim of this research was to create a ...composite material with enhanced dielectric properties compared to each individual component, and to investigate the electrical properties of the composites, using impedance spectroscopy. The structural and morphologic properties were analyzed using X-ray diffraction and scanning electron microscopy, respectively. Impedance spectroscopy measurements were performed over a wide frequency range (100–0.1 GHz) and temperature (45–170 °C) to evaluate the electrical behavior of the material. The dielectric relaxations were analyzed using the Havriliak–Negami function, and the key electrical parameters such as relaxation frequency, dielectric strength, and electrical conductivity were extracted. Several relaxation processes were identified, which depend on the mixture of the initial titanate and ferrite materials, and a correlation between structural, morphologic, and electrical properties was exposed. The sample with the highest dielectric constant was the 25 wt% gadolinium ferrite composite, with ε′ close to 240 and loss tangent values below 0.1, affording it the more appropriate composition for energy storage devices such as lead-free dielectric capacitors.
The advent of molecular tools, and particularly next-generation sequencing, has dramatically changed our knowledge of the diversity of microbial life on Earth. In recent decades, many studies on ...different terrestrial environments have described the intriguing diversity and abundance of Euzebyales/Euzebyaceae/Euzebya, yet its role in the geochemical cycle of elements is unknown. In addition, as far as we know, no Euzebya isolates have been obtained from terrestrial niches. In this review, it is shown that Euzebya and other haloalkaliphilic bacteria can thrive under harsh conditions, such as high concentrations of sodium and/or calcium, high electric conductivity and alkaline pH, highly variable temperatures, and water fluctuations. These conditions are quasi-extreme in the studied terrestrial environments. However, the culture media used so far for isolation have failed to reproduce the original conditions of these terrestrial ecosystems, and this is likely the reason why strains of Euzebya and other bacteria that inhabit the same niche could not be isolated. It is expected that culture media reproducing the environmental conditions outlined in this review could cope with the isolation of terrestrial Euzebya and other haloalkaliphilic genera.
Ellipsometry is widely used to determine the thermo-optical properties of thin polymer films. However, if the thermo-optic coefficient (TOC) and the linear thermal expansion coefficient (LTEC) are to ...be used to determine the temperature coefficient of electronic polarizability (TCEP) in thin polymer films, their values must be determined with the greatest possible accuracy, as both have the opposite effect. In this article, we analyze changes in ellipsometric parameters resulting from changes in the thin film temperature in order to develop a data analysis method for temperature-dependent spectroscopic ellipsometry that will facilitate the accurate determination of thermo-optical parameters, including the TCEP, in polymer thin films. As practical application examples, we identified optimal spectral windows to accurately determine the thermo-optical parameters of 50 to 150 nm-thick PMMA thin films deposited on Si and SiOsub.2 substrates. The influence of thin-film thickness on the accuracy of TOC and LTEC determination is discussed.
A new layered magnetic topological insulator with the composition MnBi.sub.0.5Sb.sub.1.5Te.sub.4 is obtained. The electrical conductivity in the plane of the layers and in the direction normal to the ...layers is studied in the range of temperatures of 1.4-300 K. It is found that a "metallic" character of the temperature dependence of the resistivity rho(T) is observed in the range of temperatures of 50-300 K in both directions. Below T = 50 K, the value of rho increases and demonstrates an uncommon temperature dependence with a characteristic feature in the region of the critical temperature T.sub.c = 23 K. The increase in the resistance in the temperature range of 50-23 K is determined by the spin fluctuations and magnetic phase transition. Below T.sub.c and down to 1.4 K, rho(T) demonstrates a behavior characteristic for the weak localization effect, which is confirmed by the analysis of the data obtained when studying magnetoresistance.
The development of efficient materials for the generation and storage of renewable energy is now an urgent task for future energy demand. In this report, molybdenum disulphide hollow sphere (MoS
-HS) ...and its reduced graphene oxide hybrid (rGO/MoS
-S) have been synthesized and explored for energy generation and storage applications. The surface morphology, crystallinity and elemental composition of the as-synthesized materials have been thoroughly analysed. Inspired by the fascinating morphology of the MoS
-HS and rGO/MoS
-S materials, the electrochemical performance towards hydrogen evolution and supercapacitor has been demonstrated. The rGO/MoS
-S shows enhanced gravimetric capacitance values (318 ± 14 Fg
) with higher specific energy/power outputs (44.1 ± 2.1 Whkg
and 159.16 ± 7.0 Wkg
) and better cyclic performances (82 ± 0.95% even after 5000 cycles). Further, a prototype of the supercapacitor in a coin cell configuration has been fabricated and demonstrated towards powering a LED. The unique balance of exposed edge site and electrical conductivity of rGO/MoS
-S shows remarkably superior HER performances with lower onset over potential (0.16 ± 0.05 V), lower Tafel slope (75 ± 4 mVdec
), higher exchange current density (0.072 ± 0.023 mAcm
) and higher TOF (1.47 ± 0.085 s
) values. The dual performance of the rGO/MoS
-S substantiates the promising application for hydrogen generation and supercapacitor application of interest.
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The lower valence compensation of YMnsub.1-xCuxOsub.3 (x = 0.00, 0.05, and 0.10) is prepared by the solid-state reaction, and the effects of divalent cation Cu-doping on the construction and magnetic ...and dielectric attributes of multiferroic YMnOsub.3 are systemically researched. Powder X-ray diffraction shows YMnsub.1-xCuxOsub.3 has a single-phase hexagonal construction with a P63cm space group as the parent YMnOsub.3, and lattice parameters decrease systematically as Cu concentration increases. Using the scanning electric microscope, structure morphologies analysis shows that the mean grain size varies between 1.90 and 2.20 μm as Cu content increases. YMnsub.1-xCuxOsub.3 magnetization increases as Cu doping concentration increases, and the antiferromagnetic transition temperature declines from 71 K for x = 0.00 to 58 K for x = 0.10. The valence distributions of Mn ions conduce to the modified magnetic attributes. Due to Cu substitution, the dielectric loss and dielectric constant decline as frequency increases from 400 to 700 K, showing representative relaxation behaviors. Indeed, that is a thermally activated process. In addition, the peak of the dielectric loss complies with the Arrhenius law. The relaxation correlates to the dipole effect regarding carrier hopping between Mnsup.3+ and Mnsup.4+, and also correlates to oxygen vacancies generated by Mnsup.2+.
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The assembly of Ga alloys with Ni or Ni alloy has been widely developed for various low-temperature applications in recent years. In the constituent Ni-Ga binary system, however, the phase ...equilibrium with the phase “NiGasub.5” and its stability has scarcely been investigated. The present study used the diffusion couple technique combined with SEM-EPMA and XRD analysis to examine the phase stability and the homogeneity range of the phase. The results show that “NiGasub.5” is a stable phase in the binary system with little homogeneity range and suggest that the peritectic reaction L+Nisub.3Gasub.7→NiGasub.5 lies between 112.0 and 115.5 °C. This work provides new information for the modification of the Ga-rich low-T region of the Ni-Ga phase diagram.
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In recent years, layered chalcogenides have attracted interest for their appealing thermoelectric properties. We investigated the Gesub.2Sbsub.2Tesub.5 compound in two different stacking sequences, ...named stacking 1 (S1) and stacking 2 (S2), wherein the Ge and Sb atomic positions can be interchanged in the structure. The compound unit cell, comprising nine atoms, is made of two layers separated by a gap. We show, using the quantum theory of atoms in molecules, that the bonding across the layers has characteristics of transit region bonding, though with a close resemblance to closed-shell bonding. Both S1 and S2 are shown to bear a similar small gap. The full determination of their thermoelectric properties, including the Seebeck coefficient, electrical conductivity and electronic and lattice thermal conductivities, was carried out by solving the Boltzmann transport equation. We show that stacking 1 exhibits a larger Seebeck coefficient and smaller electrical conductivity than stacking 2, which is related to their small electronic gap difference, and that S1 is more suitable for thermoelectric application than S2. Moreover, under certain conditions of temperature and doping level, it could be possible to use S1-Gesub.2Sbsub.2Tesub.5 as both a p and n leg in a thermoelectric converter. Under biaxial, tensile and compressive strains, we observe that the thermoelectric properties are improved for both S1 and S2. Furthermore, the increase in the power factor of S1 in the cross-plane direction, namely perpendicular to the gap between the layers, shows that strains can counteract the electronic transport hindrance due to the gap.
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Bronze metal matrix composites (MMCs) are futuristic materials that may find applications in automobile, aviation, and marine industries, specifically for propellers in submarines, bearings, and ...bushings for defence purposes. The present investigation studied the effect of Sisub.3Nsub.4 (5, 10, 15 wt%) ceramic particles on the physical, metallurgical, and tribological behaviour of Cu-10Sn/Sisub.3Nsub.4 MMCs. Cast rods of three composites and a base alloy were fabricated using the liquid metallurgy route. The microstructural characterisation for the cast samples was conducted using FESEM (Field Emission Scanning Electron Microscope), EDS (Energy Dispersive Spectroscopy), XRD (X-ray diffraction), and TEM (Transmission Electron Microscope), which revealed that the Cu-10Sn alloy reinforced with 5 wt% of Sisub.3Nsub.4 had homogeneous distribution and perfect bonding of the Sisub.3Nsub.4 with the bronze MMC. The dry sliding wear test was performed by varying parameters such as the applied load (10, 20, 30 N) and sliding velocity (1, 2, 3 m/s). The specific wear rate (SWR) increased against an increased load. However, the SWR and coefficient of friction decreased and then increased against an increasing sliding velocity due to tribolayer formation. The primary wear mechanism observed at low and high loads was severe delamination. In contrast, the wear mechanism was adhesion wear at high and low velocities. Amongst the researched samples, Cu-10Sn/5 wt% Sisub.3Nsub.4 composites revealed the least SWR at a load of 10 N and sliding velocity of 2 m/s and hence can be recommended for manufacturing bearings and bushings in the automobile and defence industry.
The success of geological carbon storage depends on the assurance of permanent containment for injected carbon dioxide (CO.sub.2) in the storage formation at depth. One of the critical elements of ...the safekeeping of CO.sub.2 is the sealing capacity of the caprock overlying the storage formation despite faults and/or fractures, which may occur in it. In this work, we present an ongoing injection experiment performed in a fault hosted in clay at the Mont Terri underground rock laboratory (NW Switzerland). The experiment aims to improve our understanding of the main physical and chemical mechanisms controlling (i) the migration of CO.sub.2 through a fault damage zone, (ii) the interaction of the CO.sub.2 with the neighboring intact rock, and (iii) the impact of the injection on the transmissivity in the fault. To this end, we inject CO.sub.2 -saturated saline water in the top of a 3 m thick fault in the Opalinus Clay, a clay formation that is a good analog of common caprock for CO.sub.2 storage at depth. The mobility of the CO.sub.2 within the fault is studied at the decameter scale by using a comprehensive monitoring system. Our experiment aims to close the knowledge gap between laboratory and reservoir scales. Therefore, an important aspect of the experiment is the decameter scale and the prolonged duration of observations over many months. We collect observations and data from a wide range of monitoring systems, such as a seismic network, pressure temperature and electrical conductivity sensors, fiber optics, extensometers, and an in situ mass spectrometer for dissolved gas monitoring. The observations are complemented by laboratory data on collected fluids and rock samples. Here we show the details of the experimental concept and installed instrumentation, as well as the first results of the preliminary characterization. An analysis of borehole logging allows for identifying potential hydraulic transmissive structures within the fault zone. A preliminary analysis of the injection tests helped estimate the transmissivity of such structures within the fault zone and the pressure required to mechanically open such features. The preliminary tests did not record any induced microseismic events. Active seismic tomography enabled sharp imaging the fault zone.
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