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Temperature-dependent distribution of silver nano particles on ferroelectric substrate: Molecular dynamics simulation
摘要： Silver nano particles have been widely used as catalyst for chemical industry. However, the catalytic efficiency of the silver has been limited by the aggregation of the silver, as the active sites are only located on the surface of the catalyst particles. In this paper we report the surface aggregation dynamics of silver on different ferroelectric polarization surface and temperature dependent behaviors. Meanwhile, reducing the particle size to obtain the dispersed morphology of silver was discussed by the dissipative particle dynamics method and density functional theory. The surface with upward polarization provides more electrons to the silver, which is responsible for the dispersed morphology of the silver.
关键词： Ferroelectrics,morphology,nano
更新于2025-09-10 09:29:36
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Ferroelectric behavior in nanocrystalline KNbO <sub/>3</sub> synthesized by a modified polymerized complex method
摘要： Effect of nanocrystalline size of the particles on ferroelectric properties of KNbO3 is studied. Properties like hysteresis parameters, phase transition temperatures and domain morphology in nanocrystallites were studied by using P-E hysteresis, differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) techniques, respectively. Nanocrystalline KNbO3 compound was synthesized by a modified polymerized complex method and room-temperature structural phase was characterized by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. Field emission gun-scanning electron microscopy (FEG-SEM) was used to reveal the size and morphology of the particles. It was found that the present nanoparticles of sizes ranging from 50 to 250 nm bears polarization values <1 lC/cm2, and undergo cubic-tetragonal and tetragonal-orthorhombic phase transitions at 312 and 87 (cid:1)C respectively. Although the value of polarization is small as compared to the bulk reported in the literature, the nature of P-E loops along with phase transitions and presence of 60, 90 and 180(cid:1) domain structures indicates retention of ferroelectric nature in KNbO3 even at the nanolevel.
关键词： domain structure,Nanocrystalline material,phase transition,ferroelectrics
更新于2025-09-10 09:29:36
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Temperature-driven phase transitions and enhanced piezoelectric responses in Ba(Ti0.92Sn0.08)O3 lead-free ceramic
摘要： Ferroelectric phases coexistence or transition is an important strategy on generating high piezoelectricity. Here, the temperature-induced phase structural evolution correlated with small signal piezoelectric response d33, bias-field piezoelectric activity dmax33 (E), unipolar and bipolar strain piezoelectric outputs d*33 in Ba(Ti0.92Sn0.08)O3 (BTS0.08) ceramic was investigated in details. Temperature-driven successive phase transitions from rhombohedral(R) to orthorhombic(O), tetragonal(T), finally to cubic(C) phases took place around 14 °C, 38 °C and 61 °C, respectively. The highest d33 value of 675 pC/N is achieved in the T-C phase transition. However, the O-T phase boundary gives the highest dmax33 = 1170 pm/V, bipolar d*33 = 822 pm/V and unipolar d*33 = 1318 pm/V. The temperature-driven phase transition exhibits large enhancements in piezoelectric property comparable to that of composition-induced phase boundary. These features suggest an effective method to design high-performance piezoelectrics by tailoring the types of phase boundary.
关键词： Phase transition,Lead-free piezoceramics,Ferroelectrics,Phase boundary
更新于2025-09-10 09:29:36
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Enhanced piezoelectric properties of Sr <sub/>(1.7)</sub> (Na <sub/>0.5</sub> Bi <sub/>0.5</sub> ) <sub/>0.3</sub> Bi <sub/>4</sub> Ti <sub/>5</sub> O <sub/>18</sub> ceramics in the system Sr <sub/> (2- <i>x</i> ) </sub> (Na <sub/>0.5</sub> Bi <sub/>0.5</sub> ) <sub/><i>x</i> </sub> Bi <sub/>4</sub> Ti <sub/>5</sub> O <sub/>18</sub> (where 0 ≤ <i>x</i> ≤ 0.5)
摘要： Fine powders synthesized via sol-gel route were employed to fabricate Sr(2-x)(Na0.5Bi0.5)xBi4Ti5O18 (SNBT, where x = 0, 0.1, 0.25, 0.3, 0.4 and 0.5) ceramics. The composition (x) dependent structural changes associated with SNBT ceramics were analyzed using X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and Raman spectroscopic techniques. Average grain size analyses carried out on the SNBT ceramics by scanning electron microscopy revealed an important role played by the dopants in inhibiting the grain growth. Dielectric constants and the Curie temperature of the ceramics were found to decrease and increase respectively with increase in x. The increase in Curie temperature with increase in x was attributed to the decrease in the tolerance factor. The specific composition (x = 0.3) of the SNBT ceramics exhibited improved piezo and ferroelectric properties associated with a higher Curie-temperature (569 K). The piezoelectric coefficient (d33) and the planar electromechanical coupling coefficient (kp) of SNBT(x = 0.3) were enhanced by 25% and 42% respectively as compared to the undoped ceramics.
关键词： Curie temperature,Ferroelectrics,Piezoelectric constant,Tolerance factor
更新于2025-09-10 09:29:36
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Origin of polar nanoregions and relaxor properties of ferroelectrics
摘要： In spite of more than 60 years of research, hundreds of publications, and dramatic influence on properties, the driving force of the formation of the polar nanoregion (PNR) in the paraelectric phase of perovskite ferroelectrics and consequent relaxor properties remains uncertain. We show that these peculiar features follow directly from the vibronic, pseudo-Jahn-Teller (PJT) theory of ferroelectricity. Due to the higher disorder (and entropy) in the paraelectric phase (created by the local PJT dynamics), as compared with the polarized phase (where the PJT dynamics is partially quenched), a small PNR of the latter with n unit cells is formed in a dipole-alignment self-assembly process. It emerges encapsulated by a border layer with intermedium ordering that produces “surface tension” and limits its size. The thermodynamic equilibrium between the PNR and the bulk cubic phase at temperatures Tn, well above the phase transition TC, is reached by compensation of the excessive entropy contribution Tn(cid:2)S with ordering energy and the work against this surface tension. The calculations based on the vibronic theory, including the PJT induced local dipolar dynamics and intercell interactions, yield the size of PNR as a function of the temperature increments Tn ? TC and some crystal parameters. In accordance with experimental data, the size of the emerging PNR decreases with temperature, n ～ (Tn ? TC)?3, becoming undetectable at the Burns temperature TB. At temperatures Tf , nearer to the phase transition, the sizes of PNRs grow rapidly, and their interaction leads to the formation of the nonergodic (glasslike) phase.
关键词： polar nanoregions,pseudo-Jahn-Teller effect,relaxor properties,ferroelectrics,vibronic theory
更新于2025-09-09 09:28:46
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The Balancing Act in Ferroelectric Transistors: How Hard Can It Be?
摘要： For some years now, the ever continuing dimensional scaling has no longer been considered to be sufficient for the realization of advanced CMOS devices. Alternative approaches, such as employing new materials and introducing new device architectures, appear to be the way to go forward. A currently hot approach is to employ ferroelectric materials for obtaining a positive feedback in the gate control of a switch. This work elaborates on two device architectures based on this approach: the negative-capacitance and the piezoelectric field-effect transistor, i.e., the NC-FET (negative-capacitance field-effect transistor), respectively π-FET. It briefly describes their operation principle and compares those based on earlier reports. For optimal performance, the adopted ferroelectric material in the NC-FET should have a relatively wide polarization-field loop (i.e., ”hard” ferroelectric material). Its optimal remnant polarization depends on the NC-FET architecture, although there is some consensus in having a low value for that (e.g., HZO (Hafnium-Zirconate)). π-FET is the piezoelectric coefficient, hence its polarization-field loop should be as high as possible (e.g., PZT (lead-zirconate-titanate)). In summary, literature reports indicate that the NC-FET shows better performance in terms of subthreshold swing and on-current. However, since its operation principle is based on a relatively large change in polarization the maximum speed, unlike in a π-FET, forms a big issue. Therefore, for future low-power CMOS, a hybrid solution is proposed comprising both device architectures on a chip where hard ferroelectric materials with a high piezocoefficient are used.
关键词： CMOS,negative-capacitance,piezoelectrics,field-effect transistor,MOS devices,power consumption,ferroelectrics
更新于2025-09-09 09:28:46
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Broadband Terahertz Spectroscopy of Phonon-Polariton Dispersion in Ferroelectrics
摘要： Electromagnetic waves at frequencies below the X-ray region strongly couple to the optical vibrational modes in a solid. These coupled excitations have been called phonon polaritons. The relationship of the polariton frequency versus the polariton wavevector shows a remarkable dispersion, especially in the vicinity of the transverse and longitudinal optical mode frequencies. The signi?cant frequency dependence enables valuable applications such as a tunable terahertz radiation source. The polariton dispersion relations of technologically important dielectric and ferroelectric crystals were reviewed in the broad terahertz range using terahertz time-domain spectroscopy, far-infrared spectroscopy, and Raman scattering spectroscopy.
关键词： terahertz,phonon polariton,ferroelectrics,spectroscopy
更新于2025-09-09 09:28:46
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An isogeometric approach to flexoelectric effect in ferroelectric materials
摘要： Flexoelectricity is an electromechanical coupling effect between the polarization and strain gradient in all dielectrics regardless of point group symmetry. Due to its significant influence on material behavior at the nanoscale, the flexoelectric effect has attracted more and more attention in recent years. In this paper, a real space phase field model for the flexoelectric effect in ferroelectric materials is developed by using isogeometric analysis (IGA). The IGA employs the same smooth and high-order basis functions to describe both the geometry of material and the solution of phase field, which is able to give an accurate and efficient description of the flexoelectric effect in ferroelectrics with arbitrary geometrical shapes and boundary conditions. To this end, phase field simulations on the effect of flexoelectricity are conducted for nanoscale ferroelectrics with different geometrical shapes and boundary conditions. The simulation results show that the flexoelectric effect has significant influence on the domain structures and domain switching of ferroelectric materials at the nanoscale. For ferroelectric nanobeam under bending load, due to the flexoelectric effect, the mechanical bending can break the symmetry of hysteresis loop between electric field and polarization. As for ferroelectric nanodots, the flexoelectric effect increases the magnitude of spontaneous polarizations and results in the tilting of polarization vortex. In addition, out-of-plane components appear in the polarization vortex of ferroelectric nanodots due to the flexoelectric effect, which increases the coercive field for the switching of polarization vortex and changes the switching process significantly. The present work not only presents an effective nonlocal model for the domain evolution in ferroelectric materials with the consideration of the flexoelectric effect, but also predicts new switching behavior of the polarization vortex due to the flexoelectric effect in ferroelectric nanodots.
关键词： Ferroelectrics,Isogeometric analysis,Flexoelectricity,Phase field model
更新于2025-09-09 09:28:46
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Orientation dependence of electric field induced phase transitions in lead-free (Na <sub/>0.5</sub> Bi <sub/>0.5</sub> )TiO <sub/>3</sub> -based single crystals
摘要： The orientation dependence of the electric field induced strain and phase transitions in 0.92(Na0.5Bi0.5)TiO3-0.06BaTiO3-0.02(K0.5Na0.5)NbO3 (NBT-6BT-2KNN) single crystals has been investigated. The evolution of Raman spectra with electric field reveals that a tetragonal ferroelectric phase is initially induced at E=14kV/cm and completed above E=25kV/cm for [001] oriented single crystals. When the electric field is applied along [111] direction, a partial phase transition from pseudocubic to rhombohedral structure is triggered at E=19kV/cm, which is higher than that for inducing tetragonal ferroelectric phase along [001] direction. Both field-induced phase structures and stability of NBT-6BT-2KNN single crystal are strongly associated with the crystallographic orientations. These results provide a better understanding to the field-induced macroscopic strain in lead-free NBT-based ferroelectrics.
关键词： X-ray diffraction,lead-free ferroelectrics,electric field induced phase transitions,Raman spectroscopy,NBT-based single crystals
更新于2025-09-09 09:28:46
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Crystal structure and electrical properties of textured Ba2Bi4Ti5O18 ceramics
摘要： Highly textured Ba2Bi4Ti5O18 ceramic was prepared by spark plasma sintering (SPS). X-ray di?raction of the ceramics revealed the coexistence of a major ferroelectric phase (Space group, SG: B2cb) and a minor paraelectric phase (SG: I4/mmm) at room temperature. A di?used phase transition was observed at around 240 °C. The evolution of the switching current peaks in the electric current vs. electric ?eld (I-E) loops with increasing temperature was interpreted by the structural changes and temperature dependent polarisation reversal processes. The slim polarisation vs. electric ?eld (P-E) loops, the extra switching current peaks in the I-E loops and the non-zero piezoelectric d33 coe?cient indicate that Ba2Bi4Ti5O18 is a relaxor ferroelectric material. The recoverable energy density (0.41 ± 0.01 J/cm3) of Ba2Bi4Ti5O18 ceramics in the perpendicular direction to the SPS pressing direction is close to that of Pb(Mg1/3Nb2/3)O3-based ceramics. The obtained results suggest Ba2Bi4Ti5O18 ceramics might be promising for energy storage applications.
关键词： Ba2Bi4Ti5O18,Texture,Relaxor ferroelectrics,Energy storage,Bismuth layer-structured ferroelectrics
更新于2025-09-04 15:30:14