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Defect dipole evolution and its impact on the ferroelectric properties of Fe-doped KTN single crystals
摘要： The ferroelectric and piezoelectric properties of doped potassium tantalum niobate crystals with different Fe doping amounts and the adjustability of the properties are investigated. The hysteresis loops and current density curves show that the defect dipoles have an obvious effect on domain reorientation, and the effect decreases with increasing doping amount. The ferroelectric and piezoelectric properties can be adjusted via the defect dipoles, and the adjustability is reduced with increasing doping amount. A change of the doping amount leads to defect dipole structure evolution in the crystals, in which the defect dipoles transform from a polar structure to a nonpolar structure, which is the reason for the transition of the domain reorientation determined by the defect dipoles. This result has proved that introducing defects is an effective way to improve and regulate perovskite properties, and the doping amount is one of the important factors controlling the defect dipoles.
关键词： Ferroelectric,domain orientation mechanism,defect dipoles,doping behavior
更新于2025-11-14 17:28:48
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Influence of aging on electrocaloric effect in Li+ doped BaTiO3 ceramics
摘要： Aging creates significant changes in the properties of the ferroelectric materials such as dielectric and piezoelectric properties. However, the influence of aging on the electrocaloric effect (ECE) has not yet been investigated. In this work, we investigate the effect of the aging on the ECE in acceptor (Li+) doped BaTiO3 ceramics. We observe that aging induced defect polarization (PD) reduces the saturation polarization of the doped samples until Tc=115 oC. Above that temperature PD loses its effectiveness and material behaves like a fresh sample. Suppression of polarization below TC due to aging effect results in a sharper slope change in the temperature dependence of electrical polarization in aged samples which causes an increase in the electrocaloric temperature change of Li+ doped BaTiO3 ceramics up to 23 % at TC. Above a critical Li doping amount, both negative and positive electrocaloric effect are observed in the same sample.
关键词： Aging,BaTiO3,Li-doping,Electrocaloric effect,Defect dipoles
更新于2025-11-14 17:28:48
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A Full-Spectrum Metal-Free Porphyrin Supramolecular Photocatalyst for Dual Functions of Highly Efficient Hydrogen and Oxygen Evolution
摘要： A full-spectrum (300–700 nm) responsive porphyrin supramolecular photocatalyst with a theoretical solar spectrum efficiency of 44.4% is successfully constructed. For the first time, hydrogen and oxygen evolution (40.8 and 36.1 μmol g?1 h?1) is demonstrated by a porphyrin photocatalyst without the addition of any cocatalysts. The strong oxidizing performance also presents an efficient photodegradation activity that is more than ten times higher than that of g-C3N4 for the photodegradation of phenol. The high photocatalytic reduction and oxidation activity arises from a strong built-in electric field due to molecular dipoles of electron-trapping groups and the nanocrystalline structure of the supramolecular photocatalyst. The appropriate band structure of the supramolecular photocatalyst adjusted via the highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels of the porphyrin gives rise to thermodynamic driving potential for H2 and O2 evolution under visible light irradiation. Controlling the energy band structure of photocatalysts via the ordered assembly of structure-designed organic molecules could provide a novel approach for the design of organic photocatalysts in energy and environmental applications.
关键词： supramolecular photocatalysts,photocatalysis,full spectrum,dual functions,dipoles
更新于2025-09-23 15:23:52
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Polarized THz Emission from In-Plane Dipoles in Monolayer Tungsten Disulfide by Linear and Circular Optical Rectification
摘要： Recent advances in the development of polarized terahertz (THz) emission from nanomaterials have not only opened up a new “TeraNano” interdiscipline but also provided a new tool for nonlinear optical process research. Herein, THz radiation mechanism of monolayer tungsten disulfide (WS2) is first investigated by both linear and circular polarization laser excitations at room temperature. The results reveal that polarized THz emission is dominated by the optical rectification based on in-plane nonlinear dipoles, which is totally different from that of bulk WS2. The mechanism is verified by the azimuthal angle and pump polarization angle dependence of THz emission in both experiment and theory. Furthermore, controllably elliptically polarized THz emission is observed with the maximum ellipticity of ≈0.52 based on nonresonant nonlinear process under the circularly polarized excitation. A clear understanding of THz radiation mechanism of 2D materials will facilitate further design, optimization, and polarization control of integrable 2D THz optoelectronics.
关键词： THz radiation,monolayer WS2,in-plane nonlinear dipoles,optical rectification,elliptically polarized THz emission
更新于2025-09-23 15:23:52
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The role of dipole structure and their interaction on the electromechanical and actuation performance of homogeneous silicone dielectric elastomers
摘要： Grafting polar groups onto elastomer chains has proven to be an effective method to achieve high performance homogenous dielectric elastomers (DE). Up to now, there still lacks an in-depth understanding of the effect of structure and content of these grafted dipoles on the electromechanical properties of the modified DE. In this study, three kinds of polar groups including carboxyl (COOH), hydroxyl (OH), and ester (COOCH3) are grafted onto Polymethylvinylsiloxane (PMVS) by using a photochemical thiol-ene reaction to prepare PMVS-COOH, PMVS-OH and PMVS-COOCH3 DE. Three grafting degrees (15%, 50% and 95%) were prepared for each kind of modified PMVS. Interestingly, although the dipolar moment of COOH is higher than that of OH and COOCH3, at the same grafting degree, the dielectric constant of PMVS-OH is much higher than that of PMVS-COOCH3 and PMVS-COOH. At high grafting degree (50% and 95%), the actuated strain at a specific electric field of PMVS-OH is significantly higher than that of PMVS-COOH and PMVS-COOCH3. The actuated train at a 15 kV/mm sharply increases from 0.2% for PMVS to 9.1% for PMVS-OH with the grafting degree of 95%, higher than that of the commercial silicone DE and the new structured silicone DE reported previously. These dielectric, mechanical and actuated properties are affected by the combined effects of moment, mobility and interactions of these dipoles, which have been deeply discussed. The present study provides guidance for the preparation of high-performance homogeneous DE by rational designing the dipolar structure and content.
关键词： Polymethylvinylsiloxane,dipoles,electromechanical properties,thiol-ene click chemistry,dielectric elastomers,actuated strain
更新于2025-09-23 15:23:52
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[Institution of Engineering and Technology 12th European Conference on Antennas and Propagation (EuCAP 2018) - London, UK (9-13 April 2018)] 12th European Conference on Antennas and Propagation (EuCAP 2018) - Single Polarization Reflectarray Design Based on an Element with Seven Parallel Dipoles to Generate Independent Beams in three frequency bands.
摘要： A single layer reflectarray element based on seven parallel dipoles is proposed for single polarization applications. The dipoles of the reflectarray element make it possible a multi-resonant behavior which provides very large phase range, while keeping low loss and low cross-polarization level. A sequential design process of a reflectarray antenna is proposed where the lengths of the dipoles are adjusted in pairs to provide three independents beams at 20, 25 and 30 GHz. The simulated radiation patterns of the reflectarray antenna exhibit efficiencies of 80%, 62% and 52% at 20, 25 and 30 GHz respectively. The maximum cross-polar radiation obtained is 29.7 dB, 32.9 dB and 39.1 dB below the maximum of the co-polar beam at 20, 25 and 30 GHz respectively. Bandwidths of 14%, 8.2% and 4.3% are achieved at center frequencies of 20, 25 and 30 GHz respectively. These bandwidth results account for a +/-0.5o of deviation in the main beam direction, for 2dB-gain variations in the two first bands, and for a 3dB gain variation in the last band.
关键词： parallel edge-coupled dipoles,single polarization,reflectarrays
更新于2025-09-23 15:23:52
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[IEEE 2018 International Conference on Electromagnetics in Advanced Applications (ICEAA) - Cartagena des Indias (2018.9.10-2018.9.14)] 2018 International Conference on Electromagnetics in Advanced Applications (ICEAA) - Antenna Pattern Effects in a Low Sidelobe Circularly Polarized Planar Array Due to Element Errors
摘要： Random amplitude and phase errors at the elements of a phased array antenna cause elevated sidelobe levels. Formulas for predicting the sidelobe levels based on the error statistics are well known. These same random errors also cause an error in the axial ratio of a circular polarized array. This paper presents some new expressions for the change in axial ratio as a function of the random errors.
关键词： antenna arrays,axial ratio,planar arrays,circular polarization,array errors,crossed dipoles
更新于2025-09-23 15:22:29
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Ferroelectric Origin and Distortion Modes in Doped BiFeO <sub>3</sub> by Crystallography Approach
摘要： There are conflicts about the ferroelectric origin and the relationship of two distortion modes, namely, the ferroelectric (FE) mode and antiferrodistortive (AFD) mode. Here the two distortion modes and enhanced ferroelectric properties (Pr=89.5 μC cm-2) are observed in BiFeO3 thin films doped with small radius Mg2+ (A-site) deposited on (111) Pt/Ti/SiO2/Si substrates by a sol-gel method, the relationship of the two distortion modes turns from cooperative to competitive as the FE mode strengthens. A new explanation of ferroelectric origin and distortion modes in doped BiFeO3 by the Defect Dipoles Driven Distortions Theory (abbreviate DDD) from crystallography is reported. Meanwhile, the crystal structure regulation mechanism of doped BiFeO3 thin films with substantially enhanced ferroelectric properties is also put forward. The distances of the positive and negative charge center in [FeO6] octahedrons evidently increase by Mg2+ doping compared with that in the Bi0.9Sm0.1Fe0.95Mn0.05O3 (BSFMO). The change of distances is contributed to the law of the atomic migration from the move of oxygen vacancies and the attraction of defect dipoles. A positive effect on ferroelectric properties of the appropriate increase in oxygen vacancies is explored, which is explained by "the probability of possible position that oxygen vacancies occurred" and "the relationship between the leakage current and the overlapping oxygen positions". The potential structure and more suitable doping ions are successfully predicted by the crystal structure regulation mechanism. In addition, it brings a new direction for the search of other structure regulation ions so as to realize the perfect ferroelectric properties for practical application, which will become an important beginning of ferroelectric materials design.
关键词： ferroelectric properties,structural distortions,crystallography,ferroelectric origin,defect dipoles
更新于2025-09-23 15:22:29
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[IEEE 2019 IEEE 8th International Conference on Advanced Optoelectronics and Lasers (CAOL) - Sozopol, Bulgaria (2019.9.6-2019.9.8)] 2019 IEEE 8th International Conference on Advanced Optoelectronics and Lasers (CAOL) - The Influence of Terahertzand Middle-Infrared Laser Radiationon the Membrane-Dependent Properties of Ratsa?? Red Blood Cells
摘要： A novel planar ultrathin electronically steerable parasitic array radiator (ESPAR) is presented in this paper. Through theoretical analysis of the electric fields of orthogonally crossed dipoles in phase quadrature, it is found that the crossed dipoles radiate linearly polarized wave with a rotational electric field in the azimuth plane. This characteristic is then utilized to design a planar crossed dipole ESPAR, termed as “CD-ESPAR.” Furthermore, a simple but effective impedance matching method is also proposed and analyzed. To verify these concepts, a prototype with compact size and very low profile (0.42 λ0 × 0.42 λ0 × 0.006 λ0) resonating at 2.3 GHz is designed, fabricated, and measured. The measured results indicate that the proposed antenna achieves more than 17.8% impedance bandwidth and can produce four directional beams, covering the whole azimuth plane. Owing to its planar ultrathin structure, compact size, electronically beam-switching ability, low power, and low cost characteristics, it is promising for applications in wireless communications.
关键词： Beam-switching,planar antenna,smart antenna,crossed dipoles,electronically steerable parasitic array radiator (ESAPR)
更新于2025-09-23 15:21:01
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Mechanisms of LiF Interlayer Enhancements of Perovskite Light-Emitting Diodes
摘要： The use of LiF as a thin interlayer between the electron transport layer and cathode has played a pivotal role in remarkable advances in perovskite LEDs (PeLEDs); however, the mechanism behind the effect of LiF remains to be fully understood. Here we report a combined experimental and computational study from which we ascribe the benefits of a LiF interlayer to the migration of dissociated Li into the cathode and dissociated F into the anode. Electronic device simulations reveal that the former improves electron injection by lowering the Schottky barrier height, while the latter reduces the barrier width. These reduce turn-on voltage and improve current density and charge balance in LEDs. We fabricate PeLEDs with and without the LiF interlayer and link these materials and electronic phenomena to the device light-current-voltage characteristics. X-ray photoelectron spectroscopy obtained in sputter profiling of PeLEDs corroborates the dissociation of LiF.
关键词： LEDs,interface dipoles,metal-halide perovskites,photoelectron spectroscopy,band alignment
更新于2025-09-23 15:21:01