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Origin of Ferroelectricity in Epitaxial Si-doped HfO2 Films
摘要： HfO2-based unconventional ferroelectric (FE) materials were recently discovered and have attracted a great deal of attention in both academia and industry. The growth of epitaxial Si-doped HfO2 films has opened up a route to understand the mechanism of ferroelectricity. Here, we used pulsed laser deposition (PLD) to grow epitaxial Si-doped HfO2 films in different orientations of N-type SrTiO3 substrates. Using piezoforce microscopy, polar nanodomains can be written and read, and these domains are reversibly switched with a phase change of 180o. Films with different thicknesses displayed a coercive field Ec and a remnant polarization Pr of approximately 4～5 MV/cm and 8～32 μC/cm2, respectively. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) results identified that the as-grown Si-doped HfO2 films have strained fluorite structures. The ABAB stacking mode of the Hf atomic grid observed by HRTEM clearly demonstrates that the ferroelectricity originates from the noncentrosymmetric Pca21 polar structure. Combined with soft X-ray absorption spectra (XAS), it was found that the Pca21 ferroelectric crystal structure manifested as O sublattice distortion by the effect of interface strain and Si dopant interactions, resulting in further crystal-field splitting as a nanoscaled ferroelectric ordered state.
关键词： HRTEM,PLD,XRD,Ferroelectricity,PFM,XAS,Epitaxial Si-doped HfO2 thin films,N-type SrTiO3 substrates
更新于2025-11-14 17:04:02
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High-efficiency synthesis of high-performance K0.5Na0.5NbO3 ceramics
摘要： Pure (K0.5Na0.5)NbO3 (KNN) ceramics with high density, fine and uniform-size grains were prepared by mechanochemical activation-assisted process. The time of synthesis is only 100 min, which is 72% - 93% shorter than the 6-24h of the conventional solid-state method. Compared to samples prepared by conventional solid-state method, both the microstructure evolvement and electric properties were explored in detail. Results show the electric properties was significantly improved. Moreover, the dielectric and ferroelectric properties of obtained KNN ceramics exhibit strong dependence on the crystal size of the initial powders. The optimized ceramics HKNN100 showed a quite high energy storage performance, i.e., large electric energy storage density (Wtol=1.612 J/cm3) and recoverable energy storage density (Wrec=0.431 J/cm3), which can be mainly ascribed to the large dielectric breakdown strength (DBS=110 kV/cm). Our works demonstrated that mechanochemical activation-assisted method possesses advantages for high-efficiency preparation of KNN or KNN-based ceramics.
关键词： Dielectric properties,Ferroelectricity,(K0.5Na0.5)NbO3 Ceramics,Mechanochemical activation,Microstructure
更新于2025-11-14 17:04:02
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Tuning Ferroelectric, Dielectric, and Magnetic Properties of BiFeO <sub/>3</sub> Ceramics by Ca and Pb Co-Doping
摘要： Effects of Ca/Pb co-doping on structure, ferroelectric, dielectric, and magnetic properties of BiFeO3 ceramics are investigated. A structure transition from a rhombohedral phase (space group R3c) to a cubic phase (space group Pm3m) with the increment of Ca/Pb concentration is revealed by X-ray diffraction and Raman spectra. In order to compensate the valence change caused by Ca2+ dopant, Pb ions present tetravalent state under the existence of Ca ions. The room-temperature ferroelectric behavior depends upon Ca/Pb co-doping and the structural transition in BiFeO3 ceramics. Meanwhile, the variation of the dielectric loss tangent in the frequency range of 102–107 Hz and the leakage current at room temperature illustrate that Ca/Pb co-doping increases resistivity and reduces leakage current. Compared with that of Sr/Pb co-doping, the co-doping of Ca/Pb has improved the leakage current by two orders of magnitude, besides further increasing the ferroelectric polarization and dielectric properties under the same co-doping concentration. In addition, enhanced ferromagnetism is observed with the increase of Ca/Pb content, which can be attributed to the effective suppression of spiral cycloidal spin structure and spin canting resulting from the structural transition.
关键词： BiFeO3,ferroelectricity,co-doping,dielectricity,ceramics,magnetism
更新于2025-09-23 15:23:52
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Mechanically-controllable strong 2D ferroelectricity and optical properties of semiconducting BiN monolayer
摘要： Structural, electronic, ferroelectric, and optical properties of two-dimensional (2D) BiN monolayer material with phosphorene-like structure are studied in terms of the density functional theory and modern Berry phase method of ferroelectric calculation. Both phonon spectra, molecular dynamics simulations, and total energy comparison indicate that the BiN monolayer is a stable 2D ferroelectric with polarization as large as 580 pC/m, with ferroelectric polarization being sustainable up to 500 K. Further study shows that the polarization in the BiN monolayer can be easily switched from [100] to [010] direction over the bridging saddle phase by applying a tensile [010] stress of 2.54 N/m or compressive [100] stress of -1.18 N/m. This phase transition makes its lattice constants vary in a large range compared to other non-ferroelectric 2D materials. Moreover, through applying uniaxial tensile stress parallel to the polarization, one can fix the polarization and change the semiconductor energy gap, from direct to indirect one. The optical properties feature a very strong anisotropy in reflectivity below the photon energy of 4 eV. All these significant ferroelectric, mechanical, electronic, and optical properties make us believe that the 2D BiN monolayer can be used to make stretchable electronic devices and optical applications.
关键词： 2D material,optical property,monolayer,mechanical manipulation,2D ferroelectricity,2D semiconductor
更新于2025-09-23 15:23:52
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Ferroelectric Polarization-Switching Dynamics and Wake-Up Effect in Si-Doped HfO <sub/>2</sub>
摘要： Ferroelectricity in ultra-thin HfO2 offers a viable alternative for ferroelectric memory. Reliable switching behavior is required for commercial applications; however, the many intriguing features of this material have not been resolved. Herein, we report an increase in the remnant polarization after electric field cycling, known as the 'wake-up' effect, in terms of the change in the polarization switching dynamics of a Si-doped HfO2 thin film. Compared with a pristine specimen, the Si-doped HfO2 thin film exhibited a partial increase in polarization after a finite number of ferroelectric switching behaviors. Polarization switching behavior was analyzed using the nucleation-limited switching model characterized by a Lorentzian distribution of logarithmic domain-switching times. The polarization switching was simulated using the Monte Carlo method with respect to the effect of defects. Comparing the experimental results with the simulations revealed that the wake-up effect in HfO2 thin film is accompanied by the suppression of disorder.
关键词： Domain switching,Ferroelectricity,Defects,FeRAM,HfO2,Thin films
更新于2025-09-23 15:23:52
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Lead-free Ag <sub/> 1-3 <i>x</i> </sub> La <sub/><i>x</i> </sub> NbO <sub/>3</sub> Antiferroelectric Ceramics with High Energy Storage Density and Efficiency
摘要： Environmentally benign lead-free bulk ceramics with high recoverable energy density (Wrec) are very attractive in advanced pulsed power capacitors. In this work, composition engineering was adopted by La3+ modification to improve the energy storage performance of Ag1-3xLaxNbO3 ceramics. It was found the antiferroelectric (AFE) phase was stabilized after La3+ substitution, as a result of the reduced tolerance factor t. Significant improvement of Wrec and energy storage efficiency (η) were achieved with value of 3.12 J/cm3 and 0.63 for x=0.02 at an electric field of 230 kV/cm, more than 1.5 times the value of pure AgNbO3 (Wrec=1.9 J/cm3, η=0.40). The excellent energy storage properties are resulted from the increased antiferroelectric-ferroelectric phase transition electric field (EF), ferroelectric-antiferroelectric phase transition electric field (EA) and breakdown electric field (Eb). The enhanced Eb was ascribed to the decreased grain size and increased electrical resistivity upon La3+ modification. The feature makes Ag1-3xLaxNbO3 a potential candidate for energy storage applications.
关键词： energy storage,ferroelectricity/ferroelectric materials,lead-free ceramics,dielectric materials/properties
更新于2025-09-23 15:22:29
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Room-temperature multiferroic and magnetodielectric properties of SrTiO3/NiFe2O4 composite ceramics
摘要： Various xNiFe2O4 ? (1-x)SrTiO3 (x = 0.04, 0.05, 0.1, 0.2) composite ceramics were prepared using sol–gel method and two-step calcination. The composite ceramics possessed no impurities and exhibited obvious magnetic properties (22.8 emu/g at x = 0.2). The magnetic second phase imposed strain effects on the SrTiO3 matrix to induce ferroelectricity. Strain values of (001) and (110) crystal planes were ~2.9% and ~1.3%. The tetragonal phase transition was evident in the Raman spectra. The remanent and maximum polarizations were 1.4 and 15.8 μC/cm2, respectively, in ceramic with 10 mol.% NiFe2O4. The dielectric permittivity was tuned with 1.6% change rate at 50 kHz and 10000 Oe.
关键词： Phase transition,Ferroelectricity,Strains,SrTiO3,Magnetodielectric
更新于2025-09-23 15:22:29
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Piezoelectric and ferroelectric characteristics of P(VDF-TrFE) thin films on Pt and ITO substrates
摘要： Organic P(VDF-TrFE) 70/30 copolymer thin films were fabricated on Pt/Ti/SiO2/Si(1 1 1) and ITO/glass substrates at 140 °C using a spin coater. Both P(VDF-TrFE) thin films exhibited ferroelectric β-phase crystallinity, as confirmed by X-ray diffraction analysis. The polarization–electric hysteresis loops of the P(VDF-TrFE) thin films on the Pt and indium-tin-oxide substrates showed high remnant polarizations of 15.5 and 11.8 μC/cm2, respectively. Atomic force microscopy characterization showed rod-like features of the P(VDF-TrFE) thin films on both substrates, where larger rod diameters were observed on the Pt substrate compared to those fabricated on the ITO substrate. Piezoelectric force microscopy measurements further confirmed the superior piezoelectric and ferroelectric properties of the P(VDF-TrFE) thin films on the Pt substrate compared to those on the ITO substrate, which arose from the increased diameter of the rod-like features.
关键词： Piezoelectricity,Ferroelectricity,P(VDF-TrFE) thin film,ITO substrate,Pt substrate
更新于2025-09-23 15:22:29
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Ferroelectric β-crystalline phase formation and property enhancement in polydopamine modified BaTiO3/poly (vinylidene fluoride-trifluoroethylene) nanocomposite films
摘要： Piezopolymer poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) films doped with BaTiO3 (BT) and polydopamine coated BT (BT-Pdop) nanoparticles were prepared by spin-coating method. Polydopamine modifies the interfaces of inorganic BT nanoparticles and PVDF-TrFE matrix with its polar hydroxyl groups, enhancing the piezoelectric β-phase. BT-Pdop nanoparticles were obtained in pH 8.5 buffer solution. For ferroelectric PVDF-TrFE, the favorable piezoelectric property comes from its ferroelectricity. Therefore, we studied the ferroelectric property of the nanocomposite films. The nanocomposite thin films possess better ferroelectric property than the pure PVDF-TrFE thin films, as demonstrated by the ferroelectric hysteresis curves. The remanent polarizations are 13.59 and 13.94 μC/cm2 after the doping of 1.0 wt% BT and 1.0 wt% BT-Pdop, respectively, which are about twice that of neat PVDF-TrFE. The piezoelectric β-ferroelectric phase increases with doping, according to X-Ray Diffraction analysis. In addition, the images of polarized optical microscopy and atomic force microscopy also reveal significant enhancement in crystallinity. The neat PVDF-TrFE is a semicrystalline polymer and the size of crystalline spherulites increases with the addition of BT and BT-Pdop nanoparticles. However, even the crystallinity of PVDF-TrFE considerably improved with polydopamine interfacial modification of BT, the increase of remanent polarization due to Pdop is only marginal. We infer that there are other defects at interfaces of BT-Pdop doped PVDF-TrFE nanocomposites which counteract the beneficial effect of the polar OH of polydopamine. Considerable enhancement on ferroelectric property of BT-Pdop doped PVDF-TrFE nanocomposites is expected after these issues are addressed.
关键词： nanoparticles,modification,crystallization,thin films,ferroelectricity
更新于2025-09-23 15:21:21
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Reducing Anomalous Hysteresis in Perovskite Solar Cells by Suppressing Interfacial Ferroelectric Order
摘要： Despite booming researches in organometal halide perovskite solar cells (PSCs) of recent years, considerable roadblocks remain for their large-scale deployment, ranging from undesirable current-voltage hysteresis to inferior device stability. Among various plausible origins of the hysteresis, interfacial ferroelectricity is particularly intriguing and warrants a close scrutiny. Here, we examine interfacial ferroelectricity in MAPbI3 (FAPbI3)/TiO2 and MAPbI3/PCBM heterostructures, and explore the correlations between the interfacial ferroelectricity and the hysteresis from the perspective of nonadiabatic electronic dynamics. It is found that ferroelectric order develops at the MAPbI3/TiO2 interface owing to the interaction between the polar MA ions and TiO2. The polarization switching of the MA ions under an applied gate field would result in drastically different rates in interfacial photoelectron injection and electron-hole recombination, contributing to the undesirable hysteresis. In a sharp contrast, ferroelectricity is suppressed at the FAPbI3/TiO2 and MAPbI3/PCBM interfaces, thanks to elimination of the interfacial electric field between perovskite and TiO2 via substitution of strong polar MA (dipole moment: 2.29 Debye) by weak polar FA ions (dipole moment: 0.29 Debye) and interface passivation, leading to consistent interfacial electronic dynamics and the absence of the hysteresis. The present work sheds light to the physical cause for hysteresis and points to the direction to which the hysteresis could be mitigated in PSCs.
关键词： Ferroelectricity,Hysteresis,Perovskite Solar Cells,Excited-state Electronic Dynamics,Electron-Hole Recombination,Orientation Selectivity
更新于2025-09-23 15:21:01