查看更多>>摘要：? 2022 Elsevier B.V.The pyrochlore with the composition Bi2FeTa2O9.5 was obtained by solid-phase synthesis. The electronic state and the nature of the local environment of iron atoms were studied by electron spin resonance (ESR) and M?ssbauer spectroscopy. In the Bi2FeTa2O9.5 ESR spectra a dipolar-broadened line with g ～ 2.05 from Fe3+ ion clusters are observed. This line is the superposition of components with widths of about 150 and 400 mT. On the low-field wing of the band, there is a feature with g ～ 4.3 relating to trace amounts of isolated Fe3+ ions in an octahedral position with a strong rhombic distortion. The M?ssbauer spectrum of the Bi2FeTa2O9.5 compound demonstrates a slightly asymmetric doublet. The form of the doublet is reproduced by a superposition of a doublet and a singlet. About 93% of the spectral area of the paramagnetic part of the spectrum falls on the Fe(III)-doublet with IS = 0.365 ± 0.0020 mm/s, QS = 0.604 ± 0.034 mm/s, correlated with Fe3+ ions in regular axial octahedral positions. The remaining part is represented by a Fe(III)-singlet with IS = 0.176 ± 0.0288 mm/s from Fe3+ ions in a symmetric environment. The electrical properties of the compound were studied at temperatures of 20 – 450 °C in the frequency range of 25 Hz – 1 MHz. It was found that synthesized ceramics exhibit dielectric properties. The permittivity and the dielectric loss tangent at 20 °C were determined and are 57 and 0.003 (1 MHz), respectively.
查看更多>>摘要：? 2022 Elsevier B.V.Bilayered vanadium oxides are attractive cathode materials for rechargeable batteries. The expanded interlayer space and versatile chemistries of these oxides yield high specific capacities. However, capacity retention and rate performance are limited due to structural instability and low electronic conductivity of these materials. Assembling the oxides with one- and two-dimensional carbon nanoparticles may produce highly efficient heterointerfaces that would enhance electrochemical charge storage properties. Here, we synthesize for the first time bilayered vanadium oxide composites with carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs). The nanostructured carbons were initially functionalized by flash oxidation in air to create polar groups on the carbon surface, producing fCNTs and fGNPs, and improve compatibility with an aqueous chemical preintercalation synthesis route. Lithium preintercalated bilayered vanadium oxide, LVO (LVO = δ-LixV2O5·nH2O), was selected as a redox active oxide component to facilitate Li+ ion diffusion through the interlayer region of δ-V2O5. A one-step process was developed to synthesize LVO/fCNT and LVO/fGNP composites by an in situ low temperature sol-gel method. We observed marked improvements in capacity retention and rate performance in the nanocomposites as compared to the pristine oxide, which were attributed to both improved electron transport and heterointerface stabilization effect enabled by integration with fCNTs and fGNPs. This work illustrates the ability to enhance material functionality through the in situ synthesis of nanocomposites with controllable heterointerface.
查看更多>>摘要：? 2022 The AuthorsErbium/ytterbium-dopped Y0.9Er0.1?xYbxVO4 samples with x = 0, 0.01, 0.05 and 0.09 were synthesized by hydrothermal synthesis at basic pH with urea addition. For comparison purposes, another sample with x = 0 was also prepared by the solgel method. X-ray diffraction patterns were indexed on the basis to a tetragonal symmetry of space group I41/amd with Z = 4 compatible with a zircon-type, in good agreement with FTIR spectra. Additionally, some of the samples were coated with silica, and the successful coating process was verified in both X-ray diffraction profiles and FTIR spectra. Particles of two different morphologies were found in transmission electron microscopy images of uncoated samples, some spherical with sizes between 14 and 20 nm and others elongated. A shell of ~ 5 nm thickness was also observed in silica covered samples. The relationship between dopant content and the luminescence emission was systematically explored. Erbium-doped samples exhibit bright green fluorescence under stimulation at 360 nm. The substitution of erbium by ytterbium successfully produced an up-conversion emission under stimulation at 808 nm, being able to observe green and red emission bands. The potential use as fluorescent thermometers of erbium/ytterbium doped samples at 300, 325 and 350 K was finally investigated.
查看更多>>摘要：? 2022 Elsevier B.V.In this paper, the magnetoelectric coupling in (x)NiFe2O4 + (1-x)BaTiO3 (0 ≤ x ≤ 1) particulate composites has been demonstrated by investigating dielectric and electron spin resonance properties. The effect of ferroelectric and magnetic phases on each other has been observed by measuring the room-temperature electron spin resonance and the dielectric properties at different temperatures and frequencies. The temperature-dependent dielectric properties at different frequencies confirm the non-relaxor ferroelectric nature of these composite samples, whereas the humps observed in the dielectric constant versus frequency plot suggest the electron hopping in a mixed spinel structure. This investigation offers a fundamental understanding of NiFe2O4 +BaTiO3 composite system for possible potential applications.
查看更多>>摘要：? 2022 Elsevier B.V.Lithium–sulfur (Li–S) batteries are expected to become efficient new-generation energy storage systems owing to their properties such as high theoretical specific capacity (1675 mAh g?1) and high energy density (2600 Wh kg?1). However, some factors restrict their rapid development; for example, the dissolution and migration of polysulfides during the charge and discharge process, extremely poor conductivity of sulfur, and increase in volume. A glass fiber separator with graphene was loaded on a surface modified by excimer ultraviolet light (EUV/graphene separator) as the separator for Li–S batteries. The modified separator was irradiated by excimer ultraviolet light with graphene powder loaded on a glass fiber via vacuum filtration; this can effectively block polysulfide diffusion and improve the utilization rate of active materials when assembled into a Li–S battery. The first discharge specific capacity for this separator was as high as 1164 mAh g?1 at 0.2 C; after 300 cycles, the specific capacity was maintained at 640.5 mAh g?1. This modified separator guarantees the efficient migration of lithium ions and effectively inhibits the shuttle effect of Li–S batteries.
查看更多>>摘要：? 2022 Elsevier B.V.Multi-metallic nanoparticles (MMNPs) attract people's attention due to their great potential in the application of energy storage, medicine, and catalysis. In this study, a simple in situ reduction method was developed to synthesize the NiCeLaFeCo and NiCeLaFeCu medium-entropy alloy (MEA) nanoparticles on nitrogen and oxygen co-doped carbon supports, with guanine and transition metal nitrates as the precursors. The prepared face-centered cubic (FCC) NiCeLaFeCo MEA nanoparticles have small particle sizes (average 21.1 nm) and medium mixing entropy (1.31 R). To extend the application of MEA nanoparticles, we have conducted a toluene cracking test regarding toluene conversion and hydrogen generation. The catalyst loaded with nickel-rich (~55.26%) MEA nanoparticles presented a high catalytic performance (over 80% conversion and 7293 ppm hydrogen generation) at 500 °C upon 2 h time-on-stream, and better catalytic performance (99% conversion and 78960 ppm hydrogen generation) at 400 °C with steam reforming. This study has provided a simple and convenient way to synthesize the functionalized carbon-based multi-metallic nanoparticles, and showed their excellent catalytic performance in the toluene cracking and hydrogen generation.
查看更多>>摘要：? 2022 Elsevier B.V.Designing hierarchical structure composite is a promising approach to overcome impedance mismatching, enrich energy loss, and acquire high microwave absorption (MA) capacity. However, obtaining stable hierarchical structure composite still remains difficulty due to the lack of precise design and uncontrolled growth. Herein, one dimensional (1D) TiO2 nanobelts coated by N-doped carbon and two-dimensional (2D) NiMoO4 nanosheets (TiO2/NC/NiMoO4) were prepared and exhibited excellent MA ability, and the minimum reflection loss (RLmin) value of it reached ? 41.1 dB at 15.1 GHz with a thickness of 3.1 mm. The outer 2D NiMoO4 and porous NC provided good impedance matching and dielectric loss, and multiple scattering behavior were introduced into the system. The 1D TiO2 offered strong anisotropy and dielectric loss. Therefore, the excellent MA performance attributed to good impedance matching, strong dielectric loss, and more interfacial polarization from the unique 1D/2D hierarchical structure.
查看更多>>摘要：? 2022 Elsevier B.V.Lightweight, flexible electromagnetic interference (EMI) shields and electromagnetic wave (EMW) absorbers with low filler and improved impedance matching is the subject of intense global research. In this work, CoFe2O4@CNTs hybrids are synthesized in situ by solvothermal method and then the flexible PVDF/CoFe2O4@CNTs composites are prepared by solution casting. The content of CNT's in the CoFe2O4@CNTs hybrids was varied between 1 and 5 wt% of the CFO. These nano-inclusions (CoFe2O4 (CFO) decorated CNTs) were dispersed in polyvinylidene fluoride (PVDF) with 7 wt%, 10 wt% and 15 wt%. The prepared systems were characterized using X-ray diffractometry, FTIR spectroscopy, transmission electron microscopy, vibrating samples magnetometry and vector network analyzer. TEM results show well dispersed CFO nanoparticles uniformly attached to the walls of CNTs, thus confirming their functionalization. Good impedance matching, which is a prerequisite for EMW absorption was observed for 7 wt% CFO@CNTs hybrid in PVDF which resulted in shielding effectiveness of 12.68 dB corresponding to 94.65% attenuation at a thickness of 1.88 mm. Moreover, EMW absorption properties of PVDF/CFO@CNTs composites were also studied by backing with metallic conductor where the same sample also showed the best minimum reflection loss (RLmin) of ?26.09 dB at 11.26 GHz (bandwidth is 0.48 GHz). Excellent absorption properties are attributed to good impedance matching, effective dielectric and magnetic loss mechanisms and formation of 3D conductive networks which facilitates multiple reflection and scattering mechanism.
查看更多>>摘要：? 2022 Elsevier B.V.Si-based anodes have revealed the potential as the next generation of lithium ion battery anode material, whereas the poor conductivity and huge volume changes during (de)lithiation process of silicon still limit their practical application. Herein, the Si/nitrogen doped carbon layer/carbon framework microspheres (SCM) are designed by nano-Si via electro-spray technology as anodes for lithium ion batteries. It has been found that the SCM consists of individual carbon-coated nano-Si primary particles linked by PAN framework, in which the carbon buffer layer can further absorb the stress of volume changes during charge/discharge process, and the carbon framework carbon framework not only provides fast diffusion path of electron, but also effectively reduces the consumption of electrolyte. Therefore, the initial columbic efficiency (ICE) of SCM anode can reach as high as 72%, and the SCM anode also shows a high specific capacity of 1192 mAh g?1 at 0.2 A g?1 and keeps a reversible capacity of 746 mAh g?1 after 200 cycles, demonstrating the as-designed SCM possesses an high ICE and a good electrochemical performance. This strategy provides a significant inspiration for fabricating high-performance Si/C anode materials of lithium-ion battery.
查看更多>>摘要：? 2022A highly efficient novel broadband NIR emission peaking at 814 nm with a large full width at half maximum (FWHM) of 170 nm was realized in novel LiGe2(PO4)3:Cr3+ (LGP:Cr3+) with internal quantum efficiency about 90% (IQE). An innovative strategy of Sb5+ codoped phosphor (LGP:Cr3+,Sb5+) led to the increases in the luminescence intensity and thermal stability. Moreover, tunable NIR emission from 814 to 743 nm was achieved which can be ascribed to the attenuation of electron-phonon coupling with increasing Sb5+-concentration. The output powers of phosphor-converted lighting emitting diodes (pc-LEDs) by combining 460 nm chips with LGP:0.01Cr3+ and LGP:0.05Cr3+,0.05Sb5+ phosphors reached 34.68 mW @ 300 mA and 40.36 mW @ 250 mA, respectively. Our results prove that the codoped strategy can provides a new idea for research on tunable NIR phosphors.
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