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Real-time observation of the temperature-induced phase transformation in GeTe and its thermal expansion properties
摘要： The GeTe-based system has long been considered as a promising candidate system for various functional applications; many of which are directly related to the polymorphic phase transformation in their crystalline forms. Consequently, the microstructure underlying their intriguing phase transition has been the subject of numerous studies. Here we provide real-time observation of the microstructural changes associated with the reversible pseudo-cubic (or rhombohedral) to cubic GeTe phase transition using high-voltage transmission electron microscopy (HV-TEM) operating at 1,250kV and complementary high-temperature X-ray diffraction (XRD). As a result of the phase transition, the pseudo-cubic GeTe domain’s configuration significantly changes from its original band-like to a spike-like morphology with a different orientation after a heating/cooling cycle. The coefficients of thermal expansion (CTE) properties as a function of temperature are also explored in relation to the GeTe phase transition.
关键词： CTE ellipsoids,in-situ high voltage transmission electron microscopy,GeTe,thermal expansion tensor,ferroelectric domains
更新于2025-09-10 09:29:36
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Effect of large-scale domain switching on intensity factors for a crack in 3D ferroelectric single crystals using the I-integral method
摘要： Due to their intrinsic brittleness, ferroelectric materials are prone to fracture under extreme electromechanical operational loads. The fracture of ferroelectric materials is usually accompanied by large-scale domain switching. This paper develops the interaction integral (I-integral) method for a crack in three-dimensional ferroelectrics through applying a virtual load increment to the current state. Unlike the widely-used switching-toughening model, the I-integral is not restricted to small scale switching. Due to designable choice of the virtual load increment, the I-integral allows to decouple the intensity factors of different fracture modes. The local intensity factors along the curved crack front can be directly extracted, since the I-integral is independent of integration volume. With these merits, the I-integral method is a very promising technique in fracture analysis of ferroelectrics under large-scale domain switching. Moreover, the I-integral method is used in combination with the phase field model to simulate a tensile test of nanoscale PbTiO3 ferroelectric single crystal with a semi-circular surface crack. Results show that various patterns of polarization pairs appear as soon as the applied load is increased beyond a critical value. The stable domain structures are divided into two layers by the plane where the crack is located and in each layers several polarization vortices formed eventually. Apart from the geometry and loading conditions, the position where the crack front is located with respect to the polarization vortex is a key factor affecting the switching-induced change of the stress intensity factor.
关键词： crack,interaction integral (I-integral),large-scale domain switching,phase field model,ferroelectric,intensity factor
更新于2025-09-10 09:29:36
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Computational design of microstructures of textured ferroelectric ceramics by phase field simulation
摘要： Grain-oriented microstructure evolutions of ferroelectric ceramics were analyzed using phase field simulations. In templated grain growth, the coarsening behavior of the template particle was investigated in detail. Although a large grain boundary energy was set in the lateral direction along the casting plane, the template particle grew mainly in the vertical direction and gradually converted from a needle-like to rectangular grain. We demonstrated a critical interval of template particles for the preparation of highly textured ceramics. Therefore, different microstructures with high degrees of texture could be fabricated by adjusting and controlling the template size and fraction. Complementary experiments were guided by the computational design. Dense ferroelectric ceramics with high degrees of texture were obtained.
关键词： Templated grain growth,Ferroelectric ceramic,Textured ceramic,Computer simulation
更新于2025-09-10 09:29:36
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The enhanced magnetoelectric effect and piezoelectric properties in the lead-free Bi3.15Nd0.85Ti3O12/La0.7Ca0.3MnO3 nano-multilayers composite thin films
摘要： The lead-free multiferroic nano-multilayers composite thin films were fabricated on basis of ferroelectric (FE) Bi3.15Nd0.85Ti3O12 (BNT) and ferromagnetic (FM) La0.7Ca0.3MnO3 (LCMO) parents with 8 nm/6 nm periodicity, respectively. The crystal structure, switching of polarization, magnetization and temperature dependence of magnetoelectric coupling (ME) effect for the multiferroic BNT/LCMO composite thin films were investigated in detail, respectively. Ferroelectric behavior along with an enhanced remnant polarization (2Pr) of 42 mC/cm2, saturated magnetization around 151 emu/cm3, the enhanced piezoelectric coefficient d33 of 263 pm/V and the enhanced magnetoelectric effect voltage coefficient of 72.1 mV/cm*Oe were obtained. The results show that the lead-free multiferroic films exhibit both good ferroelectric, dielectric and magnetic properties, as well as the enhanced ME effects, indicating that the coupling effects of electric and magnetic field exist in the fabricated Bi3.15Nd0.85Ti3O12/La0.7Ca0.3MnO3 (BNT/LCMO) nano-multilayer thin films, and the strong ME effect originating from the magnetic-mechanical-electric interaction and interface coupling were demonstrated. These results can be particularly important for developing nano-composite multiferroic devices.
关键词： Temperature dependence of ME effect,Lead-free BNT/LCMO nano-multilayers,Ferroelectric properties,Magnetization
更新于2025-09-10 09:29:36
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Electrically Responsive Materials and Devices Directly Driven by the High Voltage of Triboelectric Nanogenerators
摘要： Smart materials with electrically responsive characteristics and devices relying on different electrostatic effects can be directly driven by triboelectric nanogenerators (TENGs). The open circuit voltage from a TENG can easily reach thousands of volts with a separation distance of a few millimeters and this high output voltage can be used to effectively drive or control some devices with high internal resistance. This kind of combination is the most straightforward way for achieving a self-powered smart system. Hence, a detailed survey of electrically responsive materials and devices that can be successfully combined with TENG is summarized, including dielectric elastomers, piezoelectric materials, ferroelectric materials, electrostatic manipulators, electrostatic air cleaners, and field emission and mass spectrometers. Moreover, key factors in determining suitable materials or devices to work with TENG are clarified and an in-depth discussion of the current challenges related to these combined systems is provided. With the cost-effectiveness and simple manufacturing process, these TENG-based composite systems have great application prospects in the field of smart mechanics, human–machine interaction systems, intelligent storage systems, self-powered microfluidic chips, portable mass spectrometers, and so on.
关键词： piezoelectric materials,mass spectrometers,electrostatic air cleaners,dielectric elastomers,electrically responsive materials,self-powered systems,field emission,electrostatic manipulators,triboelectric nanogenerators,ferroelectric materials
更新于2025-09-10 09:29:36
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Site occupancy and electric-field induced strain response of Er-doped (Bi0.4Na0.4Sr0.2)TiO3 ceramics
摘要： Er-doped (Bi0.4Na0.4Sr0.2)TiO3 powders were prepared by solid state reactions according to A-site donor (Bi0.4-x/3Na0.4-x/3Sr0.2-x/3Erx)TiO3 (x ? 0.0.015 and 0.02) and B-site acceptor (Bi0.4Na0.4Sr0.2)Ti1-yEryO3 (y ? 0, 0.015 and 0.02) substitutional doping mechanisms. In both cases, room-temperature X-ray diffraction analyses revealed a decrease of the unit cell volume with increasing Er contents, suggesting A-site occupancy to be thermodynamically more favourable. Over the 25e175 (cid:2)C temperature range, A-site doped ceramics, in particular x ? 0.015, showed enhanced thermal stability of the maximum achievable electric-?eld induced strain. Importantly, this minor doping level also reduced dielectric loss at high temperature and led to a transition from non-ergodic to ergodic relaxor behaviour. These results may further motivate the study of the impact of other minor dopants in this family of Pb-free piezoceramics.
关键词： Erbium,Strain,Ceramics,Ferroelectric
更新于2025-09-10 09:29:36
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Dielectric, Ferroelectric, and Magnetic Properties of Sm-Doped BiFeO3 Ceramics Prepared by a Modified Solid-State-Reaction Method
摘要： Sm-doped BiFeO3 (BFO) material was prepared using a modified solid-state-reaction method, which used fast heating and cooling during the sintering process. The Sm doping level varied between 1 mol % to 8 mol %. Processing parameters, such as sintering temperature and annealing temperature, were optimized to obtain high-quality samples. Based on their dielectric properties, the optimum sintering and annealing temperatures were found to be 300 ?C and 825 ?C, respectively. Leakage-free square-shaped ferroelectric hysteresis loops were observed in all samples. The remnant polarization was maximized in the 5 mol %-doped sample (~35 μC/cm2). Furthermore, remnant magnetization was increased after the Sm doping and the 8 mol%-doped sample possessed the largest remnant magnetization of 0.007 emu/g. Our results demonstrated how the modified solid-state-reaction method proved to be an effective method for preparing high-quality BiFeO3 ceramics, as well as how the Sm dopant can efficiently improve ferroelectric and magnetic properties.
关键词： dielectric,Sm dopant,magnetic,ferroelectric,BFO
更新于2025-09-10 09:29:36
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Orientation Dependence of Power Generation on Piezoelectric Energy Harvesting Using Stretched Ferroelectric Polymer Films
摘要： The piezoelectric vibration energy harvesters were fabricated by using uniaxially stretched poly (vinylidene difluoride/trifluoroethylene) copolymer (P(VDF/TrFE)) film, and the relationship between piezoelectric power generation and molecular orientation was investigated. The molecular orientation in the stretched P(VDF/TrFE) films was evaluated with polarized Fourier transfer infrared (FT-IR) spectra measurement. In stretched films, the main-chains of P(VDF/TrFE) were aligned along the stretching direction. The piezoelectric properties and the electric power generation of stretched P(VDF/TrFE) films were strongly depended on their molecular orientation, measuring by cantilever-type energy harvesters. The piezoelectric coefficient(e) and output power observed in the energy harvester with the film stretched in the longitudinal direction of cantilever were 16.9 mC/m2 and 222 nW, respectively. These values were approximately 2.1 and 3.5 times these of the unstretched elements.
关键词： P(VDF/TrFE),piezoelectric,molecular orientation,energy harvesting,ferroelectric polymer
更新于2025-09-10 09:29:36
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Electric-field-controllable nonvolatile multilevel resistance switching of Bi <sub/>0.93</sub> Sb <sub/>0.07</sub> /PMN-0.29PT(111) heterostructures
摘要： Electric-field switchable multilevel nonvolatile resistance states are achieved at room temperature in Bi0.93Sb0.07/0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3(111) (PMN-0.29PT) heterostructures. During the initial poling of the PMN-0.29PT, the variation of the resistance of the Bi0.93Sb0.07 film with the electric field tracks the variation of the electric-field-induced in-plane strain of the PMN-0.29PT effectively, revealing that the resistance switching is dominated by the ferroelectric-domain-switching-induced lattice strain but not the domain-switching-induced polarization charges. A relative resistance change DR/R ≈ 7% at 300 K and up to ≈10% at 180 K were achieved near the coercive field EC of the PMN-0.29PT(111) substrate. At least five stable resistance states with good endurance properties could be obtained at room temperature by precisely controlling the electric-field pulse sequence as a result of the nonvolatile remnant strain transferring from the PMN-0.29PT to the film, providing a simple and energy efficient way to construct multistate resistive memory.
关键词： Bi0.93Sb0.07/PMN-0.29PT(111) heterostructures,nonvolatile,multilevel resistance switching,ferroelectric-domain-switching-induced lattice strain,electric-field
更新于2025-09-10 09:29:36
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Asymmetric Resistive Switching Dynamics in BaTiO <sub/>3</sub> Tunnel Junctions
摘要： The resistive switching associated with polarization reversal is studied in detail in ferroelectric BaTiO3 tunnel junctions, with focus on the dynamics of the ferroelectric domain switching. It is observed that the transition between the high-resistance state (HRS) and the low-resistance state (LRS) is largely asymmetric being smooth from LRS to HRS, but proceeds via avalanches in the HRS-to-LRS transitions. It is shown that this distinct behavior is related to the presence of an imprint field in the junction and has important consequences on the junction’s performance.
关键词： ferroelectric tunnel junctions,ferroelectric dynamics,neuromorphic computing,BaTiO3 films,memristors
更新于2025-09-09 09:28:46