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Dielectric and Transport Properties of Strontium Modified Calcium Copper Titanate
摘要： The present article provides the detailed study of the effect of strontium on the structural, microstructural, dielectric and electrical characteristics of strontium modified calcium copper titanate (i.e. Ca0.95Sr0.05Cu3Ti4O12, referred as CSCTO further) synthesized by a cost-effective ceramic processing technology. The structural analysis carried out suggests a cubic symmetry in the prepared sample. The dielectric relaxation and electrical conduction mechanism of CSCTO were studied using various powerful spectroscopic tools (i.e dielectric and impedance). Study of temperature dependence of dielectric permittivity exhibits very high (giant) dielectric permittivity (5 (cid:1) 103) and low loss factor at low frequency (1 kHz) at an intermediate temperature (315 (cid:3)C). Structure–properties relationship and conduction mechanism have been studied in a wide frequency (103–106 Hz) and temperature (25–315 (cid:3)C) range. At region of low frequency and high temperatures, there is a dominant role of the interface and Maxwell–Wagner dielectric relaxation mechanism in CSCTO bulk ceramic. The grain, grain boundary and electrode contributes towards the capacitive and resistive property of the sample are discerned from Nyquist plot. The ferroelectric (P–E) loop of the sintered CSCTO bulk sample at room temperature showed a lossy hysteresis loop. These findings further promote the capabilities of CSCTO as a base for supercapacitor.
关键词： X-Ray diffraction,supercapacitor,ferroelectric phase,microstructure,dielectric properties
更新于2025-09-23 15:23:52
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A non-isothermal phase-field model for piezo–ferroelectric materials
摘要： We propose a model for the study of piezo–ferroelectric materials, based on the Ginzburg–Landau approach to the ferroelectric transition, in which the inelastic deformation is a direct function of the ferroelectric polarization. The non-isothermal effects related to the phase change and other dissipative phenomena are considered by a suitable energy balance equation, according to the restrictions of the second principle. The hysteresis phenomena for polarization and inelastic strain are considered from both the energetic perspective of the vector Ginzburg–Landau equation and the dissipation-dominated perspective of the rate-independent evolutionary equations.
关键词： Ferroelectric,Phase field,Ferroelastic,Non-isothermal model,Hysteresis
更新于2025-09-23 15:22:29
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Computational study of nonlinear dielectric composites with field-induced antiferroelectric-ferroelectric phase transition
摘要： Electric field-induced antiferroelectric-ferroelectric phase transition and the associated nonlinear dielectric behavior in particulate composites are investigated for achieving a high dielectric capacity. A phenomenological thermodynamic model based on the Landau theory is first developed to discuss the generic phenomena of a temperature-electric field phase diagram, coexistence of antiferroelectric and ferroelectric phases, field-induced antiferroelectric-ferroelectric phase transition, and nonlinear dielectric behavior. The model is then used to carry out the phase field simulation of particulate nonlinear dielectric composites. It is found that the composites exhibit nonlinear dielectric behaviors, and the depolarization field in the composites helps reduce the dielectric hysteresis and enhance the reversibility of antiferroelectric-ferroelectric phase transitions, which are desired for energy storage applications. The simulations also reveal the underlying domain-level mechanisms for nucleation and growth processes of the phase transitions. It is shown that the macroscopic properties of the composites sensitively depend on the directional alignment of the antiferroelectric filler particles, and thus the filler morphology is an effective control variable in designing nonlinear dielectric composites.
关键词： phase field simulation,energy storage,nonlinear dielectric composites,Landau theory,antiferroelectric-ferroelectric phase transition
更新于2025-09-23 15:21:01
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Phase-field modeling of domain evolution in ferroelectric materials in the presence of defects
摘要： The properties of ferroelectric devices are strongly influenced, besides crystallographic features, by defects in the material. To study this effect, a fully coupled electromechanical phase-field model for 2D ferroelectric volume elements has been developed and implemented in a Finite Element code. Different kinds of defects were considered: holes, point charges and polarization pinning in single crystals, as well as grain boundaries in polycrystals, without and with additional dielectric interphase. The impact of the various types of defects on the domain configuration and the overall coercive field strength is discussed in detail. It can be seen that defects lead to nucleation of new domains. Compared to the energy barrier for switching in an ideal single crystal, the overall coercive field strength is significantly reduced towards realistic values as they are found in ferroelectric devices. Also the simulated hysteresis loops show a more realistic shape in the presence of defects.
关键词： polycrystalline ferroelectric,phase-field modeling,microstructural defects
更新于2025-09-19 17:15:36
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Influence of additives on structure and ferroelectric properties of NBT-BT-BMT ceramics
摘要： Influence of various over stoichiometric additives on phase formation, unit cell parameters, microstructure, dielectric and ferroelectric properties of solid solutions 0.8[0.8(Na0.5Bi0.5)TiO3-0.2BaTiO3]-0.2Bi(Mg0.5Ti0.5)O3 system has been studied. The unit cell volume slightly decreased in case of the V2O5 additives but did not change in case of Bi2O3, LiF, and KCl additives. Increase in dielectric parameters ert and tandrt values at the room temperature was revealed for compositions doped by KCl additives, while these parameters decreased in compositions doped by the V2O5 additives. Linear correlation between piezoelectric coefficient d33 measured for separate grains using the Piezoresponse Force Microscopy method and dielectric permittivity ert values at the room temperature was confirmed.
关键词： ferroelectric phase transitions,additives,dielectric properties,perovskite structure,Ceramics (Na0.5Bi0.5)TiO3 - BaTiO3 - Bi(Mg0.5Ti0.5)O3
更新于2025-09-10 09:29:36
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The effect of the length of terminal n-alkyl carboxylate chain on self-assembling and photosensitive properties of chiral lactic acid derivatives
摘要： A new series of photosensitive azo materials possessing a chiral alkyl lactate moiety and terminal n-alkyl carboxylate unit close to the azo group has been synthesised and studied. The length of the n-alkyl carboxylate chain has been systematically varied in order to establish the effect of the molecular structure on the self-assembling behaviour. Two series of materials possessing hexyl and dodecyl alkyl chains in the chiral part of the molecule have been studied. It has been shown that the length of both the alkyl chains strongly influences the mesomorphic behaviour, however, each chiral/achiral chain has different utility to tune the mesomorphic properties. With exception of the compound with the longest chains, all studied compounds exhibited the chiral tilted ferroelectric smectic C* phase. Based on the combination of terminal alkyl chains, chiral nematic, orthogonal smectic A*, and twist grain boundary smectic A* phases have been detected on cooling beyond the SmC* phase. The presence of the photosensitive functional N=N group in the molecular core allowed further tuning of the material properties by UV light illumination. The E-to-Z photoisomerization of the azo group and subsequent thermal back-isomerisation have been studied in solution by nuclear magnetic resonance and most importantly in the mesophases on bulk samples. We report on UV-induced isothermal switching from chiral smectic and nematic mesophases directly into the isotropic phase, respectively, and differences in the textures of mesophase upon restoration of the ordered liquid.
关键词： E-Z isomerisation,ferroelectric phase,photosensitive liquid crystals,azo group,chiral liquid crystals,NMR spectroscopy,optical switches
更新于2025-09-09 09:28:46
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Stabilization of ferroelectric Hf <sub/>x</sub> Zr <sub/>1?x</sub> O <sub/>2</sub> films using a millisecond flash lamp annealing technique
摘要： We report on the stabilization of ferroelectric HfxZr1?xO2 (HZO) films crystallized using a low thermal budget millisecond flash lamp annealing technique. Utilizing a 120 s 375 ?C preheat step combined with millisecond flash lamp pulses, ferroelectric characteristics can be obtained which are comparable to that achieved using a 300 s 650 ?C rapid thermal anneal. X-ray diffraction, capacitance voltage, and polarization hysteresis analysis consistently point to the formation of the ferroelectric phase of HZO. A remanent polarization (Pr) of ～21 μC/cm2 and a coercive field (Ec) of ～1.1 MV/cm are achieved in 10 nm thick HZO layers. Such a technique promises a new alternative solution for low thermal budget formation of ferroelectric HZO films.
关键词： low thermal budget,ferroelectric HfxZr1?xO2 films,remanent polarization,ferroelectric phase,millisecond flash lamp annealing,coercive field
更新于2025-09-04 15:30:14