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Electro-optic evolution driven by static and relaxational nano ferroelectric domains in KTa <sub/>1a??x</sub> Nb <sub/>x</sub> O <sub/>3</sub>
摘要： Polar nano-regions (PNRs), whose evolution and response mechanism are unclear, were identified to be responsible for the pivotal large electro-optic (EO) coe?cients near the TC in KTa1(cid:2)xNbxO3 (KTN) crystals. To investigate this phenomenon, the temperature dependence of its Raman spectrum, and of its linear e?ective and quadratic EO coe?cients, were investigated. Our results showed that both the relaxational nano-domains driven by biased electric fields under ordered static domains and strong anisotropy determined by the deformation of the NbO6/TaO6 realize enhancements of EO properties in the vicinity of Tf. We expect this understanding of the dynamic EO characteristics to be valuable for developing photonic devices and for providing a basis for exploring the origin of giant EO and piezoelectric e?ects in disordered ferroelectrics and relaxors.
关键词： KTa1(cid:2)xNbxO3,Ferroelectrics,Polar nano-regions,Raman spectrum,Electro-optic
更新于2025-09-19 17:13:59
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A method for determining the orientation of [011] poled relaxor ferroelectric single crystal disks
摘要： A new method for determining the crystal orientation of [011] poled relaxor ferroelectric single crystal (RFSC) disks has been developed. This Technical Note describes the measurement techniques and mathematical approaches associated with this new method, which is possible due to the anisotropic response of [011] poled single crystal disks. Experimentally, the disks are subject to a distributed edge load at a series of angular orientations, with the output voltage recorded at each orientation. Equations have been developed to govern a particle swarm to find an optimised fit to the experimental data yielding the crystal orientation of the disk which is required for practical applications. Approximate values for the piezoelectric charge constants d31, d32 are also determined. The method is demonstrated on a RFSC Mn-PMN-PZ-PT disk, comparing favourably with a synchrotron x-ray transmission diffraction study on the same disk.
关键词： particle swarm,piezoelectric charge constant,crystal orientation,single crystal,relaxor ferroelectrics
更新于2025-09-19 17:13:59
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Light-controlled molecular resistive switching ferroelectric heterojunction
摘要： Molecular ferroelectrics have attained significant advancement as a promising approach towards the development of next-generation non-volatile memory devices. Herein, the semiconducting-ferroelectric heterojunctions which is composed of molecular ferroelectrics (R)-((cid:1))-3-hydroxlyquinuclidinium chloride together with organic charge transfer complex is reported. The molecular ferroelectric domain provides polarization and bistability while organic charge transfer phase allows photo-induced charge generation and transport for photovoltaic effect. By switching the direction of the polarization in the ferroelectric phase, the heterojunction-based devices show non-volatile resistive switching under external electric field and photocurrent/voltage induced by light excitation, stable fatigue properties and long retention time. Overall, the photovoltaic controlled resistive switching provides a new route for all-organic multiphase non-volatile memories.
关键词： Molecular ferroelectrics,photovoltaic effect,heterojunctions,non-volatile memory,resistive switching
更新于2025-09-16 10:30:52
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Optically Engineered Nonlinear Photonic Structures in Ferroelectrics
摘要： Performance of many optical devices based on frequency conversion critically depends on spatial modulation of the nonlinear optical response of the materials. This modulation ensures, via the quasi phase matching (QPM), an efficient energy exchange between optical waves at different frequencies. The QPM structures, also known as the nonlinear photonic crystals, offer a variety of novel properties and functionalities that cannot be obtained in uniform nonlinear crystals. Typically, such nonlinear structures have been fabricated via electric-poling. However, this technique is restricted to particular crystallographic geometries, and does not allow to create isolated structures inside the nonlinear material. This means that one cannot realize fully 3-dimensional nonlinear structures via traditional electrical poling. In this work we discuss our novel technique capable of engineering quadratic nonlinearity, based on all-optical poling of ferroelectrics. This new approach, is similar to traditional laser writing in optical media. It involves a tight focusing of femtosecond infrared beam and subsequent its two photon absorption which heats locally the medium. The large temperature gradient induces thermoelectric field which, if sufficiently high, inverts locally direction of spontaneous polarization, changing the sign of nonlinearity. The method is extremely flexible, can be applied to different crystallographic orientations and enables formation of localised spatially modulated nonlinear response inside optical media. Here, we demonstrate its application to create structures for efficient frequency conversion in Lithium Niobate waveguides and transverse second harmonic generation. Moreover, we provide here the first ever experimental evidence of the 3D Nonlinear Photonic Crystal, fabricated in ferroelectric barium calcium titanate. Finally we show formation of multiple nonlinear photonic crystals in form of fork structures inside the bulk of ferroelectric calcium barium niobate, and demonstrate their application for wave-shaping in frequency doubling process, directly creating second harmonic optical vortices and conical beams.
关键词： frequency conversion,nonlinear photonic structures,ferroelectrics,all-optical poling,second harmonic generation,quasi phase matching
更新于2025-09-12 10:27:22
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Dielectric properties of self-assembled spherulite films of organic ferroelectric 2-methylbenzimidazole
摘要： Thin films of organic ferroelectric 2-methylbenzimidazole (MBI) were grown by evaporation method on different substrates. The films consist of self-assembled spherulite blocks formed by elongated crystallites of MBI. Temperature, frequency, and electric field amplitude variations of in-plane hysteresis dielectric loops were measured using interdigital system of electrodes and compared with analogous dependences in MBI single crystals. Simulation of remnant polarization Prem dependence on amplitude of electric field Emax in films is carried out in frames of a model considering the dipole moment of block as a sum of dipole moments of crystallites, which form spherulite with account of different orientation of crystallites relative to applied electric field. Deviations from the model are assosiated with complicated domain structure and presence of depolarizing fields.
关键词： Split crystals,organic ferroelectrics,polarization switching
更新于2025-09-12 10:27:22
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Design for Highly Piezoelectric and Visible/Near-Infrared Photoresponsive Perovskite Oxides
摘要： Defect-engineered perovskite oxides that exhibit ferroelectric and photovoltaic properties are promising multifunctional materials. Though introducing gap states by transition metal doping on the perovskite B-site can obtain low bandgap (i.e., 1.1–3.8 eV), the electrically leaky perovskite oxides generally lose piezoelectricity mainly due to oxygen vacancies. Therefore, the development of highly piezoelectric ferroelectric semiconductor remains challenging. Here, inspired by point-defect-mediated large piezoelectricity in ferroelectrics especially at the morphotropic phase boundary (MPB) region, an efficient strategy is proposed by judiciously introducing the gap states at the MPB where defect-induced local polar heterogeneities are thermodynamically coupled with the host polarization to simultaneously achieve high piezoelectricity and low bandgap. A concrete example, Ni2+-mediated (1–x)Na0.5Bi0.5TiO3-xBa(Ti0.5Ni0.5)O3–δ (x = 0.02–0.08) composition is presented, which can show excellent piezoelectricity and unprecedented visible/near-infrared light absorption with a lowest ever bandgap ≈0.9 eV at room temperature. In particular, the MPB composition x = 0.05 shows the best ferroelectricity/piezoelectricity (d33 = 151 pC N–1, Pr = 31.2 μC cm–2) and a largely enhanced photocurrent density approximately two orders of magnitude higher compared with classic ferroelectric (Pb,La)(Zr,Ti)O3. This research provides a new paradigm for designing highly piezoelectric and visible/near-infrared photoresponsive perovskite oxides for solar energy conversion, near-infrared detection, and other multifunctional applications.
关键词： photovoltaics,ceramics,ferroelectrics,perovskite oxides,semiconductors
更新于2025-09-10 09:29:36
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Recent Advances in Porous Ceramics || Physical Properties of Porous Pure and Zr/Sn-Doped Nanocrystalline BaTiO3 Ceramics
摘要： Polycrystalline BaTiO3 and Ba(Ti0.96SnxZr0.04-x)O3 ceramics (x=0.02-0.04) were prepared by a combination of solid-state and mechanochemical process and characterized at room temperature by X-ray diffraction for phase composition. Their crystal structures were found to be of the cubic and tetragonal symmetries, respectively. The grain size and porosity which were determined using Field Emission Scanning Electron Microscope (FESEM) and densitometer, respectively showed decrease and increase of relative density respectively, with increase in doping concentration. The variations of dielectric constant and loss with frequency and temperature show a maximum dielectric constant of 1660 at room temperature for Ba(Ti0.96Sn0.03Zr0.01)O3. The remnant polarization (Pr) and coercive field (Ec) of BT were found to be 581.73 V/cm and 0.27 μC/cm2. Increase in Sn content led to an increase in Pr of 0.58, 3.07, 3.73 C/cm2, and Ec of 1766.8, 2855.7, 2661.1 V/cm, respectively and are expected to lead to a significant reduction in the thickness of the multilayer ceramic capacitors. Impedance spectroscopy of polycrystalline Ba(Ti0.96Sn0.02Zr0.02)O3 in a wide frequency and temperature range showed Nyquist plots with presence of grain and grain boundary at 400°C and a negative temperature coefficient of resistance (NTCR) for Ba(Ti0.96Sn0.02Zr0.02)O3. The dielectric relaxation showed a non-Debye character.
关键词： porous ceramics,barium titanate,doping,MLCC,ferroelectrics
更新于2025-09-10 09:29:36
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AIP Conference Proceedings [Author(s) NATIONAL CONFERENCE ON RECENT ADVANCES IN EXPERIMENTAL AND THEORETICAL PHYSICS (RAETP-2018) - Jammu, India (17–18 April 2018)] - Optical tunability in Er3+ substituted Sr0.7Bi2.2Nb2O9 (BLFS) multifunctional ceramics
摘要： Conventional solid-state method has been used to produced bismuth layered ceramics of Sr0.7Bi2.2-xErxNb2O9 (SBN-xEr, x=0.0,0.4,0.6,0.8,1). Microstructure of all the samples were very dense. The structural and optical properties of the ceramics were investigated successfully.Under the excitation of 250 nm, Er3+ substituted Sr0.7Bi2.2Nb2O9has four intense emission bands peaking around 424 (violet), 444 (violet), 464 (Blue), 478 (Blue). In the present work SBN, well known ferroelectric material, beside the ferroelectric property, shows remarkable optical property because of Er3+ substitution. This feature of Er3+dopedSBN sample can be good for optoelectronic-device application. This also indicates that SBN-xEr ceramics can be used for high temperature optical application.
关键词： Bismuth layer structured ferroelectrics (BLSFs),Excitation,Photoluminescence
更新于2025-09-10 09:29:36
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Photoluminescence and ferroelectric behaviors related to Sr/Ba ratio in Eu3+ doped (Sr Ba1-)0.98Eu0.02Nb2O6 multifunctional tungsten bronze ceramics
摘要： The lead-free Eu3+ doped (SrxBa1-x)0.98Eu0.02Nb2O6 (SBEN, 0.3 (cid:2) x (cid:2) 07) ceramics were fabricated by conventional solid-state reaction method. Eu3+ was chosen as a dopant with the goal of inducing strong red-emitting photoluminescence based on their electrical properties. Effects of Sr/Ba ratio on the crystal structure, dielectric, ferroelectric and photoluminescent properties of SBEN ceramics were investigated by changing x. Single tungsten bronze structure with P4bm space group was obtained for all ceramics. The ceramics grain morphology varied obviously from homogenous equiaxed shape to anisometric pillar-type shape with increasing x. According to the dielectric spectra, the obtained SBEN ceramics transited from normal ferroelectrics to relaxor ferroelectrics, accompanied by the gradual decrease of Tm with increasing Sr2+ amount in A-sites. Two strong emitting peaks corresponding to the orange magnetic dipole transitions (594 nm, 5D0/7F1) and red electric dipole transitions (618 nm, 5D0/7F2) were obtained for all SBEN ceramics. The red/orange-emitting ratio of Eu3+ related to the Sr/Ba ratio in the composition was studied in this work to discuss the ions occupying situation in different A-sites.
关键词： Relaxor ferroelectrics,Dielectric properties,Luminescence,Tungsten bronze structure
更新于2025-09-10 09:29:36
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Outstanding piezoelectric properties, phase transitions and domain configurations of 0.963(K0.48Na0.52)(Nb0.955Sb0.045)O3?0.037(Bi0.50Na0.50)HfO3 ceramics
摘要： Requirements for substituting the current lead-based piezoelectric materials with lead-free ones are becoming increasingly strong from environmental concerns. In this article, we report piezoelectric properties, phase transitions and domain configurations of a dense 0.963(K0.48Na0.52)(Nb0.955Sb0.045)O3?0.037(Bi0.50Na0.50)HfO3 lead-free ceramic prepared through solid-state reaction by two-step sintering. It has a large piezoelectric coefficient d33 = 512 pC/N and a planner eletromechanical coupling coefficient kp ≈ 0.54 at room temperature. Dielectric measurement indicates that rhombohedral-orthorhombic, orthorhombic-tetragonal, and tetragonal-cubic phase transitions upon heating process occur at ?30 °C, 57 °C and 238 °C, respectively. X-ray diffraction analysis shows that the crystalline structure is dominantly of orthorhombic phase at room temperature. Domain configurations were investigated by acid etching technique. The poled ceramic shows domain patterns of long parallel stripes with hierarchical nanodomain structure existing in some broad stripes. The observed outstanding piezoelectric properties are ascribed to the rhombohedral-orthorhombic and orthorhombic-tetragonal phase transitions, and to the characteristic domain structure.
关键词： Phase transitions,Piezoelectricity,Lead-free ceramics,Ceramics,Ferroelectrics,Domain structure
更新于2025-09-10 09:29:36