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Hard/soft nanocomposites (NCs) of SrNi0.02Zr0.02Fe11.96O19 (SrNiZr)/MFe2O4 (M = Mn, Co, Cu, and Zn) were prepared using a one-pot sol-gel auto-combustion technique. All produced samples showed smooth M − H curves and single peaks on the dM/dH against H curves. This indicates that complete exchange-coupled effects between phases were achieved. Furthermore, the squareness ratio SQR=(Mr/Ms) was obtained and found to be higher than 0.5 at 300 K. This refers to the occurrence of excellent exchange coupling behavior among the soft and hard ferrites, and their structures consist of a single magnetic domain. The electrodynamic parameters were investigated in the 2–18 GHz frequency band using a coaxial line. The dependences of the real and imaginary parts of μ and e as a function of frequency were determined from the measured S-parameters. A strong correlation between the chemical composition of the soft magnetic phase and the electrodynamic parameters of the composite was observed. This was analyzed in terms of the atomic weight and configuration of the electronic shells of the A-cation in the soft phase. The electromagnetic absorption (EMA) of the investigated composites was estimated from the reflection losses calculated from μ and e. The maximal EMA value was observed.

Gd3+-substituted nano-sized Sr-hexaferrite, SrGd(x)Fe(12-x)O19 (0.00

This work reports the pulsed laser deposition of n-type selenium (Se) doped bismuth telluride (Bi2Te2.7Se0.3) and n-type bismuth telluride (Bi2Te3) nanostructures under varying substrate temperatures. The influence of the substrate temperature during deposition on the structural, morphological and thermoelectric properties for each phase was investigated. Density functional theory (DFT) simulations were employed to study the electronic structures of the unit-cells of the compounds as well as their corresponding partial and total densities of states. Surface and structural characterization results revealed highly crystalline nanostructures with abundant grain boundaries. Systematic comparative analysis to determine the effect of Se inclusion into the Bi2Te3 matrix on the thermoelectric properties is highlighted. The dependence of the thermoelectric figure of merit (ZT) of the nanostructures on the substrate temperatures during deposition was demonstrated. The remarkable room temperature thermoelectric power factor (PF) of 2765 μW/mK2 and 3179 μW/mK2 for pure and Se-doped Bi2Te3 compounds respectively, signifies their potential of being useful in cooling and power generation purposes. The room temperature ZT values of the Se-doped Bi2Te3 was found to be 0.92, about 30% enhancement as compared with the pure phase, which evidently results from the suppressed thermal conductivity in the doped species caused by phonon scattering at the interfaces.

Thermoelectric (TE) materials have increasingly entranced the attention of researchers globally, with a view to providing alternative routes to clean energy. This work reports the first thermal conductivity measurement on pulsed laser deposited Bi2Se2.7Te0.3 (BTS) thin films by a non-contact and optical-based method. Structural characterization revealed well-crystalline films whereas the scanning electron microscope images show abundant grains typical of the BTS nanostructures. A highly stoichiometric composition was observed under energy dispersive spectroscopy. The film's first-order temperature coefficient was estimated by varying the substrate temperature using advanced Raman spectrometer equipped with an inbuilt Linkam stage. The linear dependence of the E2g phonon mode on temperature and excitation laser power was harnessed to estimate the value of the suspended film's room temperature thermal conductivity. The first-order temperature coefficient was measured to be 0.0359 c m − 1 K − 1 . The low thermal conductivity measured at room temperature ( κ ~ 1.12 Wm − 1 K − 1 ) is comparable to previously reported values obtained using different conventional techniques. This work proved the potential of Raman spectroscopy to estimate the thermal conductivity as an excellent alternative tool to the existing expensive and laborious techniques. In addition, this work demonstrated that BTS is an excellent material for thermoelectric energy harvesting.

Pr Co–substituted calcium copper titanate (CCTO) ceramic with chemical composition Ca1-xPrxCu3-yCoyTi4O12 (x = 0.0, 0.1, 0.2, 0.3 and y = 0.0, 0.4, 0.5, 0.6) was synthesized by the sol-gel method. The X-ray diffraction patterns indicate that all the synthesized samples exhibit a pure phase of CCTO ceramic with absence of secondary phases such as CaTiO3 and CuO. The weight losses observed in the thermogravimetric analysis graph cease to occur at 895 ° C, indicating the formation of the final CCTO product. Field-emission scanning electron microscopy micrographs show dense and closely arranged faceted grains with the absence of agglomeration and liquid oxide phase. Energy-dispersive X-ray spectroscopy spectra confirm the stoichiometry of the synthesized CCTO ceramic, and Raman analysis rules out the presence of secondary phases; hence, the purity of the synthesized CCTO ceramic is further supported by Raman and energy-dispersive X-ray spectroscopy spectra. The optical band gap increased with Pr Co substitution, and a maximum value of 3.88 eV was obtained in the sample with x = 0.0/y = 0.0. The dielectric properties are explained on the basis of a Maxwell-Wagner relaxation process. The sample with x = 0.0/y = 0.0 shows the highest room-temperature dielectric constant (4920) at a frequency of 100 Hz. The lowest value of the room-temperature dielectric loss tangent (0.194) at 100 Hz was observed in the sample with x = 0.1/y = 0.4. The Cole-Cole plot indicates that most of the contribution to the dielectric properties of the synthesized CCTO ceramics originates from grain-boundary resistance.

Pressure engineering is a conventional approach to modify the material’s interatomic bond length, density, forces as well as other intrinsic properties. The effects of hydrostatic pressure on the electronic and thermoelectric properties of n-type halide perovskite CsSnI3 have been investigated using first-principles approach with spin–orbit coupling included. Electronic structure analysis illustrates that the material is a direct gap semiconductor. The partial charge density calculation suggested that electrons from Cs atoms do not contribute to the valence bonding instead assist in balancing the overall charge distribution. The material’s bandgap decreases with applied pressure up to 1.7 Gpa, where band inversion was observed, after which further compression widened the energy gap. Accompanying with Boltzmann's theory, it was shown that CsSnI3 is a potential candidate for thermoelectric energy harvesting. Hence, materials modification through pressure application is an effective approach to tune the electronic structure and thermoelectric properties of CsSnI3. We achieved the optimum ZT of 1.26 at 1 Gpa pressure and 600 K temperature, close the band inversion region.

An exponential increase in performance and stability of perovskite solar cells (PSCs) has been observed in the last decade, reaching over all power conversion efficiency up to 22.1%. This made them the most promising rival to the third generation silicon-based solar cells. However, there are still several issues to resolve to promote PCS's outdoor applications and commercialization. PSCs showed varying degree of sensitivity towards moisture, oxygen, temperature, and UV illumination, depending on the materials used. Other factors also influencing PSCs performance are the stability of carrier lifetime and current–voltage hysteresis. This review is focused on the parameters directly and indirectly affecting the PCSs stability and performance. Recent in-depth studies on different stability parameters are discussed for better understanding of these issues and possible solutions.

Nano-confined supercooled water occurs frequently in aqueous-organic aerosol nanodroplets that are ubiquitous in the atmosphere and in many industrial processes such as natural gas refining. The structure of these nanodroplets is important because it influences droplet growth and evaporation rates, nucleation rates, and radiative properties. We used classical molecular dynamics (MD) simulations to study the structures of binary water-butanol nanodroplets for several temperatures and droplet sizes. Water-butanol cross interactions are calculated using a Lennard-Jones (LJ) potential with non-bonded specific parameters adjusted to reproduce the experimentally observed mutual solubilities of water-butanol at 295 K. To compare with the results of the density functional theory (DFT) of aqueous-organic nanodroplets [Phys. Chem. Chem. Phys., 2006, 8, 1266-1270], we focus on T = 250 K. Our simulations show three different nanodroplet structures depending on the butanol concentration. For low concentrations, we observe a core-shell (CS) structure in which a butanol shell completely wets a water-rich core. For high concentrations, a well-mixed (WM) structure occurs as the water and the butanol become fully miscible. For intermediate concentrations of butanol, we find a distinct phase-separated Russian Doll-Shell (RDS) structure. This RDS structure consists of a roughly ellipsoidal water-rich droplet partially wetted by a well-mixed water/butanol convex lens (RD) and this lens-on-sphere structure is coated by a thin shell of butanol. We also examined the stability of our RDS structure at a higher temperature and found that at 295 K, the RDS structure had transformed into a well-mixed droplet, presumably due to the increase in the mutual solubility of water and butanol. Finally, we performed calculations using classical density functional theory for conditions that should favor the RDS structure. The results closely resembled those found using MD.

This review discusses the recent progress and persistent challenges toward achieving high thermoelectric (TE) figure of merit with inorganic TE materials. For decades, the interdependence between the relevant thermoelectric parameters has been the main impediment halting the large-scale usage of these materials for clean energy production. The thermoelectric performance can be improved by reducing the thermal conductivity or maximizing the power factor. We summarized the state-of-the-art methodologies adopted to reduce the lattice thermal conductivity to its amorphous limit, thus enhancing the figure of merit. The synergistic approach of utilizing valence band convergence, carrier filtering together with resonant levels formation has also been found to improve the power factor and the figure of merit of some TE materials. The work gives particular emphasis to systems in which spectacular advances have been demonstrated, such as chalcogenides, Heusler compounds, clathrates, and skutterudites. We further summarized different materials fabrication techniques with their success in tuning the TE performance. A discussion on future perspective where both the power factor and the thermal conductivity can be significantly tuned via a multi-scale approach to yield high-performance TE materials for industrial applications has been presented.

The demand of the multifunctional nanospinel ferrites (NSFs) is ever-increasing for various advanced applications wherein the fundamental knowledge of the magnetic features became essential. In this view, high purity NSFs of composition (Mn0.5Zn0.5)[EuxNdxFe2-2x]O4 (0.00 ≤ x ≤ 0.05) were synthesized via the ultrasonic irradiation. The influence of the co-substituents (Eu3+/Nd3+) concentration on the microstructures, morphologies and magnetic behaviors of these as-prepared NSFs were evaluated. The samples were characterized thoroughly using diverse analytical instruments. The X-ray powder diffraction patterns of these NSFs verified their phase purity. The SEM and TEM analyses revealed the existence of spherical shaped grains with size around 20 nm. The produced NSFs showed a superparamagnetic (SPM) behavior at room temperature and ferromagnetic (FM) behavior at very low temperatures. Both saturation and remanent magnetization values of the studied NSFs were improved at lower Eu3+/Nd3+ contents up to x = 0.02 and then dropped beyond x > 0.02. It was shown that the magnetic traits of these NSFs can be tailored by controlling the Eu3+/Nd3+ concentrations.

This work reports the preparation of ternary Cu/Ni/Bi2Te2.7Se0.3 nanocomposite thin films using pulsed laser deposition. For comparison, pure Bi2Te2.7Se0.3 (BTS) sample as well as Cu/Bi2Te2.7Se0.3 and Ni/Bi2Te2.7Se0.3 nanocomposites were also fabricated. Morphological characterizations of all the samples revealed smooth films typical of BTS. Energy dispersive spectroscopy demonstrated that the metals existed in the film at a trace amount. X-ray photoelectron spectroscopy showed that both Cu and Ni existed in the nanocomposites as metallic atoms i.e. free from oxidation and telluride formation. Structural characterizations using X-ray diffraction and Raman spectroscopy for all the films showed peaks corresponding to pure BTS structure suggesting that the dopants are embedded in the BTS matrix only at the grain boundaries. The ternary nanocomposites were prepared using a special configuration at three different concentrations of the Cu/Ni elements. The highest room temperature thermoelectric figure of merit (ZT) of 0.97 was observed for the optimum doping concentration (BTS-2Cu/Ni) due to a simultaneous increase in the power factor (2988 μW/mK2) and decrease in the thermal conductivity (0.93 W/mK). The increase in the thermoelectric power factor for the optimum metals doping is because of the filtering of less energetic charge carriers which enhanced the Seebeck coefficient of the material.