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Evolution of the infrared emissivity of Ni during thermal oxidation until oxide layer opacity
摘要： The mid-infrared (3–22 μm) emissivity of high-purity Ni has been studied in its pure state, during an isothermal oxidation in air at 730 °C and in the fully oxidized state. Measurements in pure Ni were performed in Ar between 200 and 800 °C and a change of slope in the temperature dependence of the total normal emissivity around its Curie temperature (354 °C) was observed. An oxidation process was carried out at 730 °C for 33 days, when the emissivity stopped evolving and the results were representative of NiO. During the ?rst stages, the emissivity evolved forming the usual interference patterns of semi-transparent ?lms. A mixture of oscillatory and monotonic behaviours of the emissivity as a function of wavelength and oxide layer thickness was found, which manifests as a non-trivial evolution of the total normal emissivity, di?erent than that reported in previous studies. Finally, the emissivity of NiO was measured from below its Néel temperature (252 °C) to 850 °C. It showed the typical shape of a ceramic material with an extra vibrational mode due to two-phonon processes and an additional absorption band around 5 μm in the antiferromagnetic phase produced by magnons. The temperature dependence of its total normal emissivity di?ers signi?cantly from that of a lightly oxidized nickel sample from the literature. Overall, the in?uence of the surface characteristics on the thermal radiative properties of oxidized Ni is thoroughly discussed and highlights the importance of accounting for all possible sources of infrared emissivity evolution in order to make accurate radiative heat transfer calculations.
关键词： Nickel oxide,Infrared emissivity,Radiometry,Radiative heat transfer,Magnetic phase transition,Nickel,Oxidation
更新于2025-09-23 15:23:52
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Cobalt doping-induced strong electromagnetic wave absorption in SiC nanowires
摘要： Understanding the electronic structure-property relationship in doped systems is a prerequisite to designing functional materials. We fabricated Co-doped SiC nanowires with different Co contents by a facile carbothermal reduction approach. The nanowires were characterized in terms of microstructure, electronic structure, and electromagnetic (EM) parameters to uncover the effect of Co dopants on enhancing the EM wave absorption ability. Microstructure analysis and density functional theory calculations verified that the doped Co species inhibited the formation of stacking faults and point defects and increased the conductivity of Co-doped SiC nanowires, which indicated the dominant role of conductivity in enhancing dielectric loss. The Co dopants also imparted the Co-doped SiC nanowires with distinct room-temperature ferromagnetic property, which led to enhanced magnetic loss and impedance matching. The induced synergism among SiC nanowires and Co dopants endowed Co-doped SiC nanowires with strong EM wave absorption ability. The minimum reflection loss of Co-doped SiC nanowires reaches (cid:1)50 dB, and the effective absorption bandwidth is 4.0 GHz with only 1.5 mm sample thickness. Thus, Co-doped SiC nanowires can be used as effective EM wave absorption materials. This study also provided a guideline for designing high-performance EM wave absorbers.
关键词： Dielectric loss,Doping,Density functional theory calculations,Electromagnetic wave absorption,Magnetic property
更新于2025-09-23 15:23:52
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Modulated up-conversion luminescence and low-temperature sensing of Gd3Ga5O12:Yb3+/Er3+ by incorporation of Fe3+ ions
摘要： Yb3+/Er3+ co-doped crystals show strong up-conversion luminescence and their temperature dependence of luminescence intensity enable the application of temperature sensors. Such sensors usually work at hundreds Kelvin with high sensitivity, while the sensors appropriate to very low temperatures are rarely reported. In this study, we report the low temperature sensing of Gd3Ga5O12:Yb3+/Er3+ nanocrystals by partial or total substitution of Ga3+ by Fe3+ ions. The up-conversion photoluminescence of the nanocrystals is measured on cooling from 300 to 4.2 K. The low-temperature sensing performance is improved, and the structure, magnetic and optical properties are modulated by the substitution of Fe3+ ions, rendering the nanocrystal useful for multi-functional sensing application.
关键词： Temperature sensor,Magnetic doping,Photoluminescence,Up-conversion
更新于2025-09-23 15:23:52
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Correlation between magneto-optical and transport properties of Sr doped manganite films
摘要： The features of electronic structure of La0.7Sr0.3MnO3, Pr0.8Sr0.2MnO3, and Pr0.6Sr0.4MnO3 polycrystalline films of different thickness have been investigated using magnetic circular dichroism (MCD) in the range of 1.1e4.2 eV. The temperature behavior of the samples electrical resistance were also has been studied. It was found that films with high Sr content (0.3 and 0.4) act as high-temperature semiconductors, while the maximum in the temperature dependences of resistivity these films indicates the transition of the samples to the metallic state at some temperature TM-S, which is different for different sample thickness. The films with the lower Sr content (0.2) act as insulators in the used temperature range. The MCD spectra have been decomposed to the Gaussian-shaped lines, and the temperature dependence of intensity of each line has been analyzed in comparison with temperature dependence of the films magnetization and with their electric conductivity type. Different temperature behavior of the intensity of four specified Gaussian-lines was revealed for semiconductor films. In the case of insulating Pr0.8Sr0.2MnO3 samples, the intensity of three specified Gaussian lines changes with the temperature in the same way as the magnetization changed. It was established that the lanthanide (La, Pr) type does not affect the MCD spectra shape for the films with the same electrical conductivity type. Besides, the correlation between the MCD data of the films and their conductivity type was revealed. Due to the detailed analysis of the specified Gaussian lines with taking into account the well-known in the literature absorption bands, lying outside the studied spectral region, the MCD bands for the studied manganite films have been identified with electronic transitions of a different nature.
关键词： Magnetic circular dichroism,Thin films,Electronic properties,Electrical transport,Crystal structure,Manganites
更新于2025-09-23 15:23:52
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Combined experimental and theoretical investigation on modulation of multiferroic properties in BiFeO3 ceramics induced by Dy and transition metals co-doping
摘要： Multiferroic Dy and transition metals (Cr, Mn, Ni) co-doped BiFeO3 ceramics were successfully synthesized by a solid-state method, and the influence on the magnetic and ferroelectric properties were investigated. Compared with Bi0.95Dy0.05Fe0.95Mn0.05O3, Bi0.95Dy0.05Fe0.95Cr0.05O3 and Bi0.95Dy0.05Fe0.95Ni0.05O3 ceramics can significantly improve the magnetic properties. The significant enhancement of magnetic properties should be related to the local ferromagnetic coupling from Cr ions (Ni ions) and Fe ions, which have already been proved by first-principles calculations. Meanwhile, both experimental and theoretical studies reveal the Dy substitution can effectively enhance the ferroelectric properties of BiFeO3. Leakage current and conduction mechanism analyses reveal that the improved ferroelectric properties are mainly attributed to the reduced oxygen vacancies.
关键词： Magnetic property,Ferroelectric property,BiFeO3,Substitution
更新于2025-09-23 15:23:52
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A series of germanotungstate-based 3d-4f heterometallic compounds with visible-light induced photocatalytic, electrochemical and magnetic properties
摘要： A series of 3d-4f heterometallic germanotungstate dimers {[Cu(dap)(H2O)3][LnCu3(dap)3(OH)3(H2O)2(GeW11O39)]}·nH2O (Ln = SmⅢ, n = 11 (1), EuⅢ, n = 12 (2), GdⅢ, n = 10 (3) and TbⅢ, n = 13 (4); dap = 1, 2-diaminopropane) have been prepared under hydrothermal conditions and structurally characterized by IR, UV-Vis, XRD, and X-ray single-crystal diffraction. Compounds 1–4 are essentially isomorphic and display organic-inorganic hybrid dimeric structures consisting of [LnCu3(dap)3(OH)3(H2O)(GeW11O39)]2 4– with two supporting [Cu(dap)(H2O)3]2+ cations on both sides. The four compounds all exhibit the excellent photocatalytic activities to delaradation of methylene blue (MB) and rhodamine-B (RhB) under visible light irradiation in the presence of H2O2. Additionally, 1–4 displays an apparent electrocatalytic activity for the reduction of hydrogen peroxide. The variable-temperature magnetic studies show that the magnetic behaviours of 1, 2 and 4 are dominated by antiferromagnetic coupling interactions, while that of 3 is ferromagnetic interactions coexist along with antiferromagnetic interactions.
关键词： Photocatalytic properties,Lacunary polyoxometalates,magnetic properties,Crystal structure,Electrocatalytic properties,3d-4f Heterometallic compounds
更新于2025-09-23 15:23:52
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The first synthesis of CdFe12O19 nanostructures and nanocomposites and considering of magnetic, optical, electrochemical and photocatalytic properties
摘要： CdFe12O19 nanostructures and nanocomposites were synthesized via sol-gel auto-combustion method. The CdFe12O19/CdTiO3 nanocomposites were prepared at 850 ?C after 1 h calcination, when molar ratio of Cd:Ti is 1:1. Effects of the molar ratio of Cd:Ti, type of precursor and calcination temperature were investigated. Both nanostructures and nanocomposites were ferromagnetic at room temperature, with saturation magnetizations (Ms) 2.561 and 11.269 emu g–1, and coercivities (Hc) 696.517 and 969.068 Oe, respectively. SEM, TEM, FTIR, EDS and XRD showed morphology, composition and particle size of the products. VSM, UV-Vis and CV were used to investigate the magnetic, optical and electrochemical properties. The band gap values of the nanocomposites were larger than that in the nanostructures. Also photocatalytic properties of the nanocomposites were investigated. This is the first attempt on the study of photocatalytic performance of the cadmium hexaferrite nanostructures and nanocomposites. The effects of various factors including composition and particle size of the nanocomposites, the Ti:Cd molar ratio and also kind of organic dye on the photocatalytic behavior of the products were evaluated. The photocatalytic activity achieved a maximum when ratio of Ti:Cd was 1:1. Methyl orange, methylene blue and methylene violet decompositions were about 71.35, 55.08 and 62.27% by nanocomposites, respectively.
关键词： Nanostructures,Photocatalytic,Optical properties,Ferrites.,Magnetic properties
更新于2025-09-23 15:23:52
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An inorganic magnetic fluorescent nanoprobe with favorable biocompatibility for dual-modality bioimaging and drug delivery
摘要： In this work, we present the development of a high water soluble biological nanoprobe through the covalent bonding of β-CD onto the surface of iron oxide?gold nanoclusters (Fe3O4@Au@β-CD). Fe3O4@Au@SiO2 NPs were also prepared for comparison. The maximum emission peak of magnetic fluorescent NPs red-shifted by 30 nm and the lifetime was also elongated to 5.21 μs after surface modified with β-CD. The relaxivities and in vitro magnetic resonance imaging ability of the resultant magnetic fluorescent NPs were also studied, indicating that Fe3O4@Au@β-CD NPs have the lowest r2/r1 ratio and could be a potential T2 contrast agent for MR imaging. The MTT assay proved that, Fe3O4@Au@β-CD NPs are of excellent water solubility and biocompatibility. In vitro confocal fluorescence imaging was also performed, manifesting that Fe3O4@Au@β-CD NPs can be selectively uptaken by gastric cancer cells (MGC-803) and exhibit red fluorescence in the cells. The preliminary drug loading and releasing measurements demonstrate that it can also act as targeted drug delivery nanosystem. All these experimental results indicate that, Fe3O4@Au@β-CD NPs hold great application perspective in the diagnosis and therapy of gastric cancer cells as biological nanoprobes.
关键词： Multifunctional,Biocompatibility,Magnetic fluorescent nanocomposites,Drug delivery,Dual-modality imaging
更新于2025-09-23 15:23:52
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Current-induced domain wall oscillations in a nanowire imaged by time-resolved photoemission electron microscopy
摘要： We study reversible domain wall motion in half-ring Ni80Fe20 nanowires on a nanosecond (ns) timescale in a truly current-induced pump-probe experiment using an energy filtered, aberration-corrected photoemission electron microscope. The x-ray magnetic circular dichroism signal is probed at different time delays before, during and after the current pulse in a stroboscopic mode with circularly polarized synchrotron radiation in the energy range of the Fe L3-edge (707 eV). We observe lateral domain wall oscillations with a frequency of ～ 0.4 GHz. Comparing the results to a proposed string model, we find that the domain wall oscillations can be described as string-like asymmetric oscillations.
关键词： Synchrotron radiation,Photoemission electron microscopy,X-ray magnetic circular dichroism,Pump-probe mode
更新于2025-09-23 15:23:52
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Luminescent, optical, magnetic and metamaterial behavior of cerium complexes
摘要： The complexes of cerium with nitrogen, oxygen and sulfur donor ligands were prepared by conventional method. These newly synthesized complexes were characterized by FTIR, UV-Vis, DART Mass, TGA, PXRD, SEM and TEM techniques. The magnetic studies were carried out by the vibrating sample magnetometer. The optical constants were measured by absorption and reflection spectra as a function of wavelength. The concentration dependence of refractive index and absorption were observed by the experimental method, which reveals that these parameters are affected by change in concentration. The optical band gap obtained from Tauc-plot indicates its probability to be a good semiconductor. The luminescence behavior of these cerium complexes were observed by the absorption and emission spectra and the emission life time were calculated by their life time spectra.
关键词： Optical band gap,Luminescence,Refractive index,Magnetic studies
更新于2025-09-23 15:23:52