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Electrical response of mixed phase (1-x)BiFeO3-xPbTiO3 solid solution: Role of tetragonal phase and tetragonality
摘要： We present the study of structural, morphological, dielectric, transport and ferroelectric properties of (1-x)BFO–xPTO solid solutions, with 0.3 ≤ x ≤ 0.6, prepared via non-conventional synthesis methods. These methods include Sol-gel and Single-step solid state method. Structural analysis revealed presence of mixed phases i.e. monoclinic (CC) and tetragonal (P4mm) phases, for all compositions showing a Morphotropic Phase Boundary. For the compositions with higher concentration of PTO, an increase in tetragonal phase fraction has been observed. Quantitative analysis showed, in general, higher value of c/a (i.e. tetragonality) for all samples as compared to the bulk PTO. The morphological analysis shows small grain size irrespective of synthesis method and composition. The low temperature frequency dependent tangent loss shows dielectric relaxation with small magnitude of dielectric constant indicating absence of extrinsic contributions. High temperature dielectric anomaly is observed around 400-500 K corresponding to magnetic phase transformation of BFO at Neel temperature which suggest the presence of magneto-electric coupling in specific compositions. Sol-gel prepared composite appeared to be more resistive than the Single-step synthesized composite and shows Arrhenius type dependence of high temperature ac conductivity. Ferroelectricity was observed in all ceramic samples which sustained high applied electric field up to 190 kV/cm. Finally, a correlation between polarization, tetragonal phase fraction and c/a ratio, has been drawn and discussed. It is concluded that c/a ratio (i.e. tetragonality) is more important parameter which can be tuned to achieve enhanced ferroelectric response as compared to the tetragonal phase fraction in (1-x)BFO–xPTO solid solutions.
关键词： Electric polarization,Non-conventional synthesis methods,Tetragonality,Morphotropic phase boundary,Ferroelectricity,Phase evolution,Dielectric anomalies
更新于2025-09-19 17:15:36
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Comparison of TiO <sub/>2</sub> and g-C <sub/>3</sub> N <sub/>4</sub> 2D/2D nanocomposites from three synthesis protocols for visible-light induced hydrogen evolution
摘要： Knowledge of the interfacial structure of nanocomposite materials is a prerequisite for rational design of nanostructured photocatalysts. Herein, TiO2 and g-C3N4 2D/2D nanocomposites were fabricated from three distinct synthetic protocols (i.e., co-calcination, solvothermal treatment and charge-induced aggregation), showing different degrees of enhancement (1.4–6.1 fold) in the visible-light induced photocatalytic hydrogen evolution reaction compared to the simple physical mixture. We propose that the interfacial Ti–O–N covalent bonding promotes the charge carrier transfer and separation more effectively than the electrostatic interaction, thus accelerating the photocatalytic H2 production. Meanwhile, the exposed surface area of TiO2 in the composite needs to be enlarged for deposition of the co-catalyst. This research sheds light on the rational design of hybrid nanocomposites based on earth-abundant elements for photocatalysis.
关键词： visible light,TiO2,nanocomposites,g-C3N4,photocatalysis,hydrogen evolution
更新于2025-09-19 17:15:36
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Electrosynthesis of Copper phosphide thin films for efficient water oxidation
摘要： A copper phosphide (Cu3P) thin film is synthesized on a Ni foam using a one-step electrodeposition method at room temperature and annealed at 300 °C in Ar atmosphere. The Cu3P film is amorphous and has a flat morphology with surface voids. It works as an electrocatalyst for water oxidation in an alkaline 1M KOH electrolyte. It exhibits excellent catalytic oxygen evolution reaction with an overpotential of 310 mV, Tafel slope of 88 mV/dec, and good stability over 20 h of operation at 10 mA/cm2. The excellent OER performance is due to its large electrochemically active surface area and low charge transfer resistance at the catalyst-electrolyte interface after the annealing.
关键词： annealing effect,Copper phosphide,oxygen evolution reaction,electrodeposition
更新于2025-09-19 17:15:36
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Far-infrared study of K giants in the solar neighborhood: Connection between Li enrichment and mass-loss
摘要： Context. A small group of red giant branch (RGB) stars are known to have anomalous Li enhancement whose origin is still not well understood. Some studies have proposed that the Li enhancement in RGB stars is correlated to their far-IR excess, a result of mass loss. Studies to confirm such a correlation have a significant bearing on our understanding of the Galactic Li enhancement. Aims. We searched for a correlation between the two anomalous properties of K giants: Li enhancement and IR excess from an unbiased survey of a large sample of RGB stars. Methods. A sample of 2000 low-mass K giants with accurate astrometry from the Hipparcos catalog was chosen for which Li abundances have been determined from low-resolution spectra. Far-IR data were collected from the WISE and IRAS catalogs. To probe the correlation between the two anomalies, we supplemented 15 Li-rich K giants discovered from this sample with 25 known Li-rich K giants from other studies. Dust shell evolutionary models and spectral energy distributions were constructed using the code DUSTY to estimate different dust shell properties, such as dust evolutionary time scales, dust temperatures, and mass-loss rates. Results. Among 2000 K giants, we found about two dozen K giants with detectable far-IR excess, and surprisingly, none of them are Li-rich. Similarly, the 15 new Li-rich K giants that were identified from the same sample show no evidence of IR excess. Of the total 40 Li-rich K giants, only 7 show IR excess. Important is that K giants with Li enhancement and/or IR excess begin to appear only at the bump on the RGB. Conclusions. Results show that K giants with IR excess are very rare, similar to K giants with Li enhancement. This may be due to the rapid differential evolution of dust shell and Li depletion compared to RGB evolutionary time scales. We also infer from the results that during the bump evolution, giants probably undergo some internal changes, which are perhaps the cause of mass-loss and Li-enhancement events. However, the available observational results do not ascertain that these properties are correlated. That a few Li-rich giants have IR excess seems to be pure coincidence.
关键词： stars: abundances,infrared: stars,stars: late-type,stars: mass-loss,stars: evolution,circumstellar matter
更新于2025-09-19 17:15:36
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Abundances of disk and bulge giants from high-resolution optical spectra
摘要： An error occurred during the production process. The subtitle of the article in the published version was "II. O, Mg, Co, and Ti in the bulge sample". Here, we correct this to "II. O, Mg, Ca, and Ti in the bulge sample".
关键词： Galaxy: evolution,Galaxy: bulge,errata, addenda,stars: abundances
更新于2025-09-19 17:15:36
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Automatic segmentation in image stacks based on multi-constraint level-set evolution
摘要： Contour extraction of image stacks is a basic task in medical modeling. The existing level-set methods usually suffer from some problems (e.g. serious errors around sharp features, incorrect split of topology and contour occlusions). This paper proposes a novel method of multi-constraint level-set evolution to avoid above-mentioned problems. Interpolation constraint and deviation constraint are added to evolution process in addition to existing constraints (such as edge points and areas). In order to prevent occlusions, it proposes a method of three-phase level-set evolution. The first phase obtains a rough contour according to selected edge points. The second phase applies an expanding LSE (level-set evolution). Missing edge points in the first phase are added when occlusions probably appear. In the third phase, occlusions are deleted and a refining evolution is implemented. As proved by final experiments, our method can steadily extract contours slice by slice when the shapes of previous contours (contours in the previous slice) are similar to current contours (contours in the current slice). Furthermore, there is no error propagation during the process of contour extraction.
关键词： level-set evolution,multi-constraint,Contour extraction
更新于2025-09-19 17:15:36
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Study of Lithium Rich Giants with the GALAH Spectroscopic Survey
摘要： In this article, we speculate on the possible mechanisms for Li enhancement origin in RGB stars based on a large data set of around 340 299 stars collected from the GALAH survey combined with the Gaia astrometry. Data has 51 982 low mass (M ≤ 2 M(cid:3)) RGB stars with reliable atmospheric parameters. The data set shows a well-populated RGB with well-defined luminosity bump and red clump with significant number of stars at each of these two key phases. We found 335 new Li-rich RGB stars with Li abundance, A(Li) ≥ 1.80 ± 0.14 dex, of which 20 are super Li-rich with A(Li) ≥ 3.20 dex. Most of them appear to be in the red clump region which, when combined with stellar evolutionary time-scales on RGB, indicates that the Li enhancement origin may lie at RGB tip during He-flash rather than by external source of merging of sub-stellar objects or during luminosity bump evolution. Kinematic properties of sample stars suggest that Li-rich giants are relatively more prevalent among giants of thin disc compared to thick disc and halo.
关键词： stars: abundances,surveys,abundances,nucleosynthesis,Hertzsprung-Russell and colour-magnitude diagrams,stars: kinematics and dynamics,stars: evolution,nuclear reactions
更新于2025-09-19 17:15:36
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New Evolutionary-Based Techniques for Image Registration
摘要： The work reported in this paper aims at the development of evolutionary algorithms to register images for signature recognition purposes. We propose and develop several registration methods in order to obtain accurate and fast algorithms. First, we introduce two variants of the firefly method that proved to have excellent accuracy and fair run times. In order to speed up the computation, we propose two variants of Accelerated Particle Swarm Optimization (APSO) method. The resulted algorithms are significantly faster than the firefly-based ones, but the recognition rates are a little bit lower. In order to find a trade-off between the recognition rate and the computational complexity of the algorithms, we developed a hybrid method that combines the ability of auto-adaptive Evolution Strategies (ES) search to discover a global optimum solution with the strong quick convergence ability of APSO. The accuracy and the efficiency of the resulted algorithms have been experimentally proved by conducting a long series of tests on various pairs of signature images. The comparative analysis concerning the quality of the proposed methods together with conclusions and suggestions for further developments are provided in the final part of the paper.
关键词： hybrid techniques,image recognition,image registration,firefly technique,evolutionary computing,affine perturbation,evolution strategies,mutual information
更新于2025-09-19 17:15:36
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Intercalated complexes of 1T′-MoS <sub/>2</sub> nanosheets with alkylated phenylenediamines as excellent catalysts for electrochemical hydrogen evolution
摘要： Two-dimensional layered MoS2 has recently been considered as an excellent catalyst for the water-splitting hydrogen evolution reaction (HER). Herein, we synthesize 1T0 phase MoS2 that was intercalated with a series of alkylated p-phenylenediamines (PDs). The substituted N atoms produced S vacancies, leading to a composition of MoS2-2xNx (x = 0.1). The more abundant methyl groups induce a larger charge transfer, resulting in excellent HER performance: for tetramethyl PD, the overpotential is 0.15 V at 10 mA cm-2 with a Tafel slope of 35 mV dec-1. The catalytic activity of the complexes depends on the concentration of the intercalated molecules, showing an optimum at a concentration of 8 mol%. First-principles calculations showed that the intercalated complexes (1T0 phase) having N atom–S vacancy (N–VS) pairs are stabilized by a large charge transfer from the PD molecules that is enhanced by the methyl groups (i.e., 0.40e–0.84e per molecule at 6.25 mol% intercalation). The charge transfer increases the density of states at and just above the Fermi level, thereby increasing the electron concentration at low cathodic bias. The active sites for the Volmer reaction are found to be N atoms in the proximal N–VS pairs. The activation barrier for the Heyrovsky reaction becomes higher at higher concentrations of the intercalants, suggesting that the experimental HER performance is also kinetically controlled.
关键词： catalysis,first-principles calculations,MoS2,hydrogen evolution reaction,intercalation
更新于2025-09-19 17:15:36
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Soluble g-C3N4 nanosheets: facile synthesis and application in photocatalytic hydrogen evolution
摘要： The high dispersibility and solubility are highly required for the potential applications and development of well-known g-C3N4 material. In this study, a facile hydrothermal treatment and the following vacuum freezing-drying process was developed to synthesize the g-C3N4 nanosheets (ca. 5 nm) with excellent dispersibility and solubility in aqueous solutions. It was found that the melem structures with many hydrophilic groups (-NH2, -OH and -C=O) were formed on the g-C3N4 nanosheet surface, resulting in the formation of soluble g-C3N4 (SCN) nanosheets. Moreover, the SCN nanosheets can be worked as the effective modifier to greatly increase the H2-production performance of conventional g-C3N4 photocatalyst (the resultant sample was referred to SCN/g-C3N4). Photocatalytic results revealed that the SCN/g-C3N4 sample exhibited a remarkably higher H2-production performance than the pure g-C3N4 by a factor of ca. 2. The improved H2-production rate of SCN/g-C3N4 photocatalysts could be primarily ascribed to the introduction of hydrophilic groups, which not only remarkably enhances the dispersibility and hydrophilicity of SCN/g-C3N4, but also work as the interfacial active sites to accelerate the H+-reduction reaction and the rapid formation of H2. The present soluble g-C3N4 nanosheets provide potential various applications in environmental protection and energy conversion fields.
关键词： photocatalysis,H2-evolution,solubility,g-C3N4 nanosheets,dispersibility
更新于2025-09-19 17:15:36