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Structural, Optical, and Dielectric Studies on Sr-Doped Biferroic YCrO3
摘要： In this work, the solid-state synthesis of Y1-xSrxCrO3 (x = 0.0, 0.1) samples has been reported. The X-ray diffraction data analysis confirmed that the synthesized samples have crystallized into the orthorhombic phase with the assigned space group Pbnm. The Rietveld refinement of the XRD data confirmed the structure and other related parameters. The slight variation in the lattice parameters and negligible shift in the reflection peaks reveals the uniform dispersion of Sr at Y-site in the parent YCrO3 matrix. The dielectric characterization revealed the good dielectric nature of the prepared samples which decreases with Sr doping. Field emission scanning electron microscopy (FE-SEM) revealed that an agglomeration type process has taken place in the sample preparation. Fourier transform infrared (FTIR) characterization witnessed the formation of orthorhombic phase of the samples under study displaying sharp absorption bands corresponding to Cr–O stretching, Y/Sr–O stretching, and O–Cr–O deformation vibration, respectively. UV-Vis spectroscopy analysis revealed the dual direct allowed bandgap of the samples assigned to the Cr3+ ion transition in the ground level.
关键词： Nanoparticles,Structure,Rietveld refinement,Morphology,Dielectric properties
更新于2025-09-23 15:23:52
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Enhanced absorption of monolayer molybdenum disulfide (MoS2) using nanostructures with symmetrical cross resonator in the visible ranges
摘要： In order to enhance the absorption of monolayer molybdenum disulfide (MoS2), a novel nanostructure with symmetrical cross resonator based on MoS2 in the visible wavelength ranges has been proposed. At a resonant wavelength of 623 nm, the absorption of monolayer MoS2 in the absorption structure is as high as 82%, much higher than the bare MoS2 in the air. The electric field around monolayer MoS2 is enhanced by the guided mode resonance, thereby enhancing the absorption of monolayer MoS2 in the structure. The relevant parameters of the proposed structure are adjusted to achieve the tunability of the resonant wavelength in the visible ranges and the high-efficiency absorption of monolayer MoS2 in the structure, which is of great significance for the applications of MoS2-based optoelectronic devices.
关键词： Absorption,Monolayer MoS2,Perfect absorption structure,Resonance
更新于2025-09-23 15:23:52
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Radar cross section reduction metasurfaces based on phase gradient and chessboard structure
摘要： In this article, wideband radar cross section (RCS) reduction metasurface is proposed. The unit of the metasurface is consisted of a noncentral symmetry hexagon patch with 2 semi-circular slots at the symmetric corners. As a result, the unit has an anisotropic response for x- and y-polarized wave. The reflection phase is varied with the radius of slots. The range of phase variation is extended by rotation of the unit with 90°. According to the generalized Snell’s Law, 4 different phase gradient supercells with dual polarization characteristics and different gradient directions are obtained. To improve the RCS reduction, chessboard structure is used. By combining these 2 technological approaches, a wideband, polarization insensitive RCS reduction is designed, which can reflect the electromagnetic wave uniformly. Both numerical and measured results show that it enables to realize a 10 dB RCS reduction in a wideband from 8.5 to 13 GHz.
关键词： chessboard structure,metasurface,phase gradient,RCS reduction,phase variation
更新于2025-09-23 15:23:52
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A Numerical Study of Densification Behavior of Silicon Carbide Matrix Composites in Isothermal Chemical Vapor Infiltration
摘要： We studied the characteristics of two-scale pore structure of preform in the deposition process and the mass transfer of reactant gas in dual-scale pores, and observed the physiochemical phenomenon associated with the reaction. Thereby, we established mathematical models on two scales, respectively, preform and reactor. These models were used for the numerical simulation of the process of ceramic matrix composites densified by isothermal chemical vapor infiltration (ICVI). The models were used to carry out a systematic study on the influence of process conditions and the preform structure on the densification behaviors. The most important findings of our study are that the processing time could be reduced by about 50% without compromising the quality of the material, if the processing temperature is 950-1 000 ℃ for the first 70 hours and then raised to 1 100 ℃.
关键词： isothermal chemical vapor infiltration,fiber preform structure,densification behavior,ceramic matrix composites,process parameters
更新于2025-09-23 15:23:52
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Analogous Anti-Ferroelectricity in Y2O3-Coated (Pb0.92Sr0.05La0.02)(Zr0.7Sn0.25Ti0.05)O3 Ceramics and Their Energy-Storage Performance
摘要： Antiferroelectric analogous (Pb0.92Sr0.05La0.02)(Zr0.7Sn0.25Ti0.05)O3 (PSLZSnT) ceramics were prepared by the solid-state sintering method by introducing a Y2O3-coating via the self-combustion method. The synthesized Y2O3-doped PSLZSnT ceramics present pseudo-cubic structure and rather uniform microstructural morphology accompanied by relatively small grain size. Excellent energy-storage performance is obtained in the Y2O3-doped PSLZSnT ceramics, in which the value of the energy-storage density presents a linearly increasing trend within the electric field measurement range. Such excellent performance is considered as relating to the rather pure perovskite structure, high relative density accompanied by relatively small grain size, and the antiferroelectric-like polarization-electric field behavior.
关键词： oxide doping,self-combustion method,energy-storage density,perovskite structure,PSLZSnT antiferroelectric-like ceramics
更新于2025-09-23 15:23:52
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Electronic Structure of Chlorophyll a Solution Investigated by Photoelectron Yield Spectroscopy
摘要： Various bio-related processes are driven by electron transfer reactions. Therefore the electronic structures of bio-molecules in their living environment are keys of their functionalities. One significant example photosynthesis which has attracted much attention due to urgent necessity of clean energy source. In this study, we carried out photoelectron yield spectroscopy (PYS) measurements to demonstrate the electronic structures of oligomerizedChl-a molecules, which is known as an essential reaction center of the photosystem in general green plants, under the atmospheric environment. The ionization energies of the Chl-a aggregates are successfully derived.
关键词： Photoelectron Yield Spectroscopy,Polarization energy,Light harvesting antenna,Photosynthesis,Photosystem,Electronic structure,Ionization energy,Reaction center,Chlorophyll a
更新于2025-09-23 15:23:52
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Influence of the intramolecular donor-acceptor distance on the performance of double-cable polymers
摘要： A series of double-cable polymers PFT-C4-PDI, PFT-C6-PDI and PFT-C8-PDI, composed of the poly(fluorene-alt-thiophene) (PFT) backbone, the perylene diimide (PDI) pendants and the length-various (four-, six- and eight-carbon) covalent alkoxy linkers, were presented. The backbone polymer chain created the hole-transporting channel and the inner-chain aggregation of PDI units created the electron-transporting channel, but the aggregation became weaker along with the longer linker, as proven by the UV-Vis absorption and fluorescence quenching. The polymers were non-conducting, but functioned as efficient compatibilizers. The doping of the polymers induced the formation of the bi-continuous networks inside P3HT:PCBM blends, facilitated photo-generated exciton dissociation and charge transporting. PFT-C4-PDI more efficiently increased the absorption coefficient and the charge-carrier mobility of the P3HT:PCBM film. The power conversation efficiency (PCE) of the P3HT:PCBM bulk-heterojunction solar cells with 3 wt% PFT-C4-PDI, PFT-C6-PDI and PFT-C8-PDI doping were improved by 16.9%, 9.2% and 8.0%, respectively, relative to the non-doped reference device.
关键词： Structure-property relationships,Energy transfer,Double-cable polymer,Polymer solar cells,Bi-continuous networks
更新于2025-09-23 15:23:52
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Fluorine-substituted TPE isomers with different triboluminescent behavior
摘要： Three isomers of fluorine-substituted tetraphenylethenes (TPE) demonstrate totally different triboluminescence (TL) behavior, as the results of their ignorable structural difference. Photophysical properties, packing model, single-crystal structure and density functional theory (DFT) calculations confirmed that bright TL emission is attributed to the high emission, intense intermolecular interaction and large dipole moments in solid state, indicating the introduction of fluorine atoms as an effective approach for realizing and modifying the TL performance.
关键词： isomer,tetraphenylethene,structure-packing-performance,fluorine-substituted,triboluminescent
更新于2025-09-23 15:23:52
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A study of the effects of ullage during the burning of horizontal PMMA and MMA surfaces
摘要： Experimental and numerical investigations of burning of horizontal surfaces of poly methyl methacrylate and methyl methacrylate are presented. A burner used in this study allows for the fuel surface to be oriented horizontally at a given distance from the burner rim. One of the aims of this study is to understand the effects of ullage (distance between burner rim and fuel surface) on the burning rate of the fuel and the flame structure. In the case of poly methyl methacrylate, the surface at an initial ullage regresses during its burning, and in the case of methyl methacrylate, the pool level is maintained at the given ullage by supplying the fuel at the rate of its burning. Careful repeatable measurements of temperature and species fields are carried out. These reveal the structure of a small‐scale pool flame established over a polymeric fluid such as methyl methacrylate, and such data are scarce in literature. In order to complement the experimental results, fire dynamics simulator is employed to simulate the experimental cases. Flame structure and flow field in the gas phase have been presented and discussed. As the ullage increases, the burning rate decreases. This trend is explained using surface convective heat flux results.
关键词： fire dynamics simulator (FDS),convective heat flux,burning rate,poly methyl methacrylate (PMMA),flame structure,ullage
更新于2025-09-23 15:23:52
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Photocatalytic Activity of ZnO Nanopowders: The role of production techniques in the formation of structural defects
摘要： The effect of the type of structural defect in zinc oxide on its photocatalytic properties was studied for phenol photodegradation under UV-irradiation. It was shown that the use of different types of precursors (zinc oxalate and zinc hydroxide) for the production of zinc oxide leads to the formation of a material with the same phase composition and equal energy of the forbidden band, but different photocatalytic activities. Simultaneously, the peculiarities of the luminescence and electron spin resonance spectra indicate the formation of different types of defects in the structure of the material, namely, oxygen vacancies (Vo) in the anionic and zinc vacancies (VZn) in the cationic sublattices of zinc oxide synthesised from the zinc oxalate and hydroxide, respectively. Also, the different characteristics of the luminescence decays reveal the different recombination paths for the free charge carriers in the systems synthesised from the different precursors. The different times of the luminescence decay also confirmed the different methods of recombination of free charge carriers in systems synthesised from different precursors. It was shown that the appearance of defects in the cationic sublattice leads to a decrease in the photocatalytic activity of the material relative to phenol degradation.
关键词： vacancies,luminescence.,Photocatalytic activity,structure defects,ZnO
更新于2025-09-23 15:23:52