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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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Internal-field-dependent low-frequency piezoelectric energy harvesting characteristics of in situ processed Nb-doped Pb(Zr,Ti)O3 thin-film cantilevers
摘要： Piezoelectric thin-film-based cantilevers have been investigated for higher energy-harvesting performance with simplified processing steps. Here, a simple in situ film deposition process of heavily Nb-doped lead zirconate titanate (PZT) films, which does not require annealing and poling, has been demonstrated to verify the possibility of use of the resultant films as energy-harvesters specifically for low frequency vibrating sources. The in situ domain formation of the films during the deposition was demonstrated from the apparent shifts of the capacitance-electric field curves, indicating the presence of internal electric fields. The so-called imprint behavior was found to be directly related to the performance of piezoelectric energy harvesting. As an optimal example, 12 mol% Nb-doped cantilever harvesters that showed the largest imprint behavior exhibited the best values of ~19.1 GPa figure-of-merit and ~1436 mWcm?3g?2 power density, which are competitive compared to other reported values.
关键词： Thin films,Cantilevers,Piezoelectric energy harvesting,Nb-doping,PZT
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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Green luminescence and calculated optical properties of Cu ions in ZnO
摘要： There are two characteristic optical transitions associated with Cu ions in ZnO, the 0.72 eV infrared and the 2.86 eV structured green luminescence (SGL). While the former is unambiguously related with the d(Cu2t) intra-shell transition, there is no generally accepted mechanism of the SGL. Besides the original model of Dingle [Phys. Rev. Lett. 23, 579 (1969)], two other mechanisms were recently proposed. We report an analysis of the optical properties of Cu in ZnO by ab initio calculations. The GGAtU approach is used, with the tU corrections applied to d(Zn), p(O) and d(Cu) orbitals. The results, compared with the available experimental data, support the Dingle's model, in which the SGL originates in the (Cu1t, hole) / Cu2t transition. A good agreement with experiment is obtained also for the internal transition at 0.72 eV. The absence of an expected radiative transition at about 2 eV is explained by its quasi-forbidden character.
关键词： Cu doping,Optical properties,Green luminescence,GGAtU calculations,ZnO
更新于2025-09-23 15:23:52
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Synthesis and characterization of Fe-doped CdWO <sub/>4</sub> nanoparticles with enhanced photocatalytic activity
摘要： The Fe-doped CdWO4 nanoparticles were successfully synthesized via a hydrothermal method. The morphology, crystal structure and photocatalytic activity of the products were characterized and investigated. The results show that the Fe-doping can enhance the photocatalytic efficiency of CdWO4 for degradation of methyl orange toxic dye. The optimal Fe/Cd atomic ratio of Fe-doped CdWO4 is identified to be 0.10. The high activity of the Fe-doped CdWO4 catalyst would be attributed to the decrease of grain size and the doped Fe ions can trap and transfer the electron–hole pairs.
关键词： doping,photocatalytic,CdWO4,methyl orange,Fe ion
更新于2025-09-23 15:23:52
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Doping induced dielectric anomaly below the Curie temperature in molecular ferroelectric diisopropylammonium bromide
摘要： A dielectric anomaly induced by doping has been observed at about 340 K in chlorine-doped diisopropylammonium bromide. The dielectric anomaly has a switchable behaviour, which indicates potential applications on switches and sensors. Temperature-dependent Raman spectrum, X-ray diffraction and differential scanning calorimetry do not show any anomaly around the dielectric anomaly temperature, which prove that the dielectric anomaly does not come from structure phase transition and has no specific heat variety. It is assumed that this dielectric anomaly can be attributed to the freezing of ferroelectric domain walls induced by the pinning of point defects.
关键词： diisopropylammonium bromide,molecular ferroelectric,doping,dielectric anomaly
更新于2025-09-23 15:23:52
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Visible light photocatalytic mineralization of bisphenol A by carbon and oxygen dual-doped graphitic carbon nitride
摘要： A facile thermal polymerization was applied to synthesize carbon and oxygen dual-doped graphitic carbon nitride (MACN) with controllable electronic band structure using malonic acid and urea as precursors. The C and O atoms substituted the sp2 N atom in graphitic carbon nitride (CN). The 1MACN (1 represented that the weight ratio of malonic acid to urea is 1% during the synthesis) with optimal band structure could decompose 15 ppm bisphenol A (BPA) within 150 min, and the mineralization rate reached to 52%. The superior photocatalytic performance of 1MACN was mainly ascribed to electronic band structure together with optical properties. On the one hand, the formation of delocalized big p bonds favored the electrons transfer after the introducing of carbon atoms. On the other hand, a positive charge density existed on the C atoms because of high electronegativity of contiguous O (3.44) that substituted N compared with C (2.55), which could attribute to high activity of MACN catalyst. The study will contribute to the further improvement of visible-light photocatalytic BPA degradation and mineralization.
关键词： BPA mineralization,Carbon-oxygen dual-doping,Visible-light photocatalytic,Graphitic carbon nitride
更新于2025-09-23 15:23:52
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by isovalent doping at the fluorite sublattice
摘要： Bismuth titanate, Bi4Ti3O12 (BiT), is a complex layered ferroelectric material that is composed of three perovskite-like units and one fluorite-like unit stacked alternatively along the transverse direction. The ground-state crystal structure is monoclinic with the spontaneous polarization (～50 μC/cm2) along the plane. BiT typically grows along the c direction in thin-film form, and having the polarization vector aligned with the growth orientation can be beneficial for several potential device applications. It is well known that judicious doping of ferroelectrics is an effective method in adjusting the magnitude and the orientation of the spontaneous polarization. Here, we show using first-principles density-functional theory and a detailed phonon analysis that Bi atoms in the fluorite-like layers have significantly more impact on the magnitude and orientation of the spontaneous polarization vector as compared to the perovskite-like layer. The low-energy hard-phonon modes are characterized by fluorite-like layers experiencing transverse displacements and large changes in Born effective charges on Bi atoms. Thus, the breaking of symmetry caused by doping of Bi sites within the fluorite-like layer leads to the formation of uncancelled permanent dipole moments along the transverse direction. This provides an opportunity for doping the Bi site in the fluorite-like layer. Isovalent dopants P, As, and Sb were studied. P is found to be most effective in the reorientation of the spontaneous polarization. It leads to a threefold enhancement of the out-of-plane component of polarization and to a commensurate rotation of the spontaneous polarization vector by 36.2° towards the transverse direction.
关键词： phonon analysis,doping,ferroelectric,Bi4Ti3O12,first-principles,polarization
更新于2025-09-23 15:23:52
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Synthesis of g-C3N4/N-doped CeO2 composite for photocatalytic degradation of an herbicide
摘要： In photocatalysis, surface engineered CeO2 could be vital due to oxygen vacancies arise from multiple valency, i.e. Ce3+ and Ce4+. This study reports photocatalytic properties of g-C3N4/CeO2 composite synthesized by a facile method in the presence of l-arginine. Physicochemical properties of g-C3N4/CeO2 material were analyzed through various characterization techniques such as XRD, UV–Vis, physisorption, etc., and correlated with its photocatalytic activity. Observed bandgap of the synthesized composite material was in the visible region, around 2.8 eV which is less than that of typical ceria, but higher than bandgap of exfoliated g-C3N4. On the further side, N doping into CeO2 was confirmed through XPS analysis. It is estimated that synthesis method aided for the N doping, which further played key role in lowering the bandgap of g-C3N4/CeO2 composite. Finally, Photocatalytic activity of g-C3N4/CeO2 composite was analyzed through degradation of an herbicide i.e. diuron, and the study revealed the good performance of the catalyst.
关键词： Graphitic carbon nitride,Photocatalysis,N doping,Herbicide,CeO2
更新于2025-09-23 15:23:52
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Creation of passivated Nb/N p-n co-doped ZnO nanoparticles and their enhanced photocatalytic performance under visible light illumination
摘要： Passivated niobium/nitrogen (Nb-N) p-n co-doped zinc oxide nanoparticles were created by a simple precipitation process with in-situ self-formed NaCl "cage" to confine the nanoparticle growth followed by the heat treatment in a flow of ammonia gas. Enhanced optical absorbance into the visible light region was observed in the Nb/N co-doped ZnO nanoparticle photocatalyst due to the Nb/N co-doping effect. It demonstrated a largely enhanced photocatalytic performance in the disinfection of Escherichia coli bacteria under visible light illumination, which could be attributed to the passivated co-doping of Nb-N to suppress the photogenerated charge carrier recombination on dopants. This robust approach for passivated p-n co-doping may also be applied to other material systems for a wide range of technical applications.
关键词： Nanoparticles,Passivated Nb/N p-n Co-doping,Photocatalyst,Zinc oxide,Visible light
更新于2025-09-23 15:23:52