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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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Plasmonic gold nanorods mediated p-BFCrO/n-rGO heterojunction in realizing efficient ferroelectric photovoltaic devices
摘要： In this work, we introduce a chemically synthesised lead-free ferroelectric thin film 2% Cr doped BiFeO3 (BFCrO) for possible photovoltaic (PV) applications. The first set of PV devices were fabricated onto ITO/glass electrode by utilizing BFCrO as an active material and Pt as top electrode. The obtained ferroelectric and electrical results were systematically compared with the conventional BFO and the BFCrO device was found to be a potential one. To further enhance the PV performance, highly conducting n-type reduced graphene oxide (rGO) was heterogeneously employed as an electron transport layer (ETL) in between ITO and BFCrO. Surprisingly, the JSC was significantly improved by 1000 times along with amended VOC and FF as compared to the standalone BFCrO device. Furthermore, an attempt has been made to embed plasmonic Au nanorods (NRs) in between rGO and BFCrO, which alleviates the absorbance in heterojunction through localized surface plasmonic effect, ultimately offered remarkable PV performances than conventional BFO one. The Au NRs based BFCrO/rGO PV device exhibited an increased VOC and JSC of 0.63 V and 2.56 mA/cm2, respectively as compared to the BFCrO/rGO device with VOC (0.56 V) and JSC (1.54 mA/cm2). Effort was devoted to establish ferroelectricity in BFCrO and the effect of positive and negative polarizations on J-V measurements were observed in with or without Au NRs based devices. The modulation in charge transport with polarization field and improved photoresponse were explained by projecting a band diagram, which also provides a comprehensive understanding on the operation principle of the fabricated devices.
关键词： Ferroelectric polarization,Heterointerface,Photovoltaic effect,Electron transport layer,Plasmon resonance
更新于2025-09-19 17:13:59
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Ferroelectric properties of gradient doped Y <sub/>2</sub> O <sub/>3</sub> :HfO <sub/>2</sub> thin films grown by pulsed laser deposition
摘要： A HfO2-based thin ?lm is a nanoscale ferroelectric material with a high-k dielectric and CMOS compatibility, which make it a promising candidate for high-performance electronics. Here, we demonstrate the synthesis of a ferroelectric Y-doped HfO2 (HYO) thin ?lm by pulsed laser deposition. This HYO thin ?lm is gradient doped by alternately depositing a HfO2 ceramic target and a Y2O3 ceramic target. In the ?lms, the orthorhombic phase, ferroelectric phase, is proved by grazing incidence x-ray diffraction and scanning transmission electron microscopy measurements. Moreover, the HYO thin ?lm embraces outstanding ferroelectric and dielectric properties, its remanent polarization is up to 10.5 lC/cm2, and the dielectric constant is 27. The 180(cid:2) inversion of the domain can be observed in a piezoelectric power microscopy image, while the phase contrast of the write domain fades with time. Therefore, this work provides a reliable approach to obtain a ferroelectric HYO thin ?lm, which enables great potential in future high-performance nanoelectronics.
关键词： pulsed laser deposition,Y-doped,ferroelectric,thin film,HfO2
更新于2025-09-19 17:13:59
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Ultrasensitive Paper-Based Photoelectrochemical Sensing Platform Enabled by the Polar Charge Carriers-Created Electric Field
摘要： Efficient separation of electron-hole pairs is vitally crucial to enhancing the analytical performance of paper-based photoelectrochemical (PEC) bioanalysis. Herein, a simple but effective strategy is developed to modulate the effective separation of photogenerated electrons and holes via introducing a polar charge carriers-created (PCC) electric field induced by a classical perovskite ferroelectric BaTiO3 (BTO). By inserting it between the n-type WO3 nanoflakes and p-type Cu2O (WO3 nanoflakes/BTO/Cu2O), the photoelectrode is endowed with a renewable PCC electric field, as a sustaining driving force, to guarantee the realization of directional separation of charge carrier (DSCC) strategy in PEC bioanalysis. The enduring PCC electric field can attract the electrons of Cu2O and holes of WO3, respectively, thereby regulating the directional migration of charge carriers and achieving an enhanced PEC photocurrent for the ultrasensitive quantification based on the highly efficient separation of electron-hole pairs. Consequently, with respect to WO3 nanoflakes/Cu2O and WO3 nanoflakes photoelectrode, the polarized WO3 nanoflakes/BTO/Cu2O photoelectrode exhibits 1.7 and 10.9 times higher photocurrent density, respectively. Benefiting from this, the prominent photocurrent density is obtained which is extremely beneficial for enhancing the sensitivity of PEC bioanalysis. Ultimately, the ultrasensitive detection of model prostate specific antigen (PSA) is realized and presented a linear range of 0.1 pg/mL-50 ng/mL with the detection limitation of 0.036 pg/mL. This work provides the basis for understanding the role of the polarized electric field induced by ferroelectric in tuning the charge separation as well as insights on strategies for constructing high-performance paper-based PEC bioanalysis.
关键词： WO3,BaTiO3,PSA,photoelectrochemical,Cu2O,ferroelectric,bioanalysis
更新于2025-09-19 17:13:59
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Design and Electro-optic investigations of de Vries smectics for exhibiting broad temperature ranges of SmA* and SmC* phases and fast electro-optic switching
摘要： In this paper we report on the design, synthesis and characterisation of two new ferroelectric liquid crystalline compounds based on using cores of (i) 5-phenyl-pyrimidine benzene and (ii) 5-phenyl-pyrimidine benzoate terminated by achiral trisiloxane chain, and chiral (S) alkyl chain on the opposite ends of their respective mesogens. These compounds exhibit broad temperature ranges of SmA* and SmC* phases, whereas the latter exists at room temperature down to 11 oC. This is one of the desirable features of the compounds for perspective applications in devices. In both compounds, the differential scanning calorimetry shows a weak first order SmA*-SmC* transition. This observation is supported by determining the critical exponent of the power law as ~0.2 that describes the dependence of the tilt angle and the spontaneous polarization on temperature. The two compounds show excellent de Vries characteristics in terms of the layer shrinkage in SmC*, the maximum shrinkage in both cases is ~ 1.5%. Furthermore (i) the birefringence decreases with a reduction in temperature instead of increasing in SmA*, and (ii) a large field-induced birefringence is observed in SmA* close to the SmA*-SmC* transition temperature, (iii) the maximum birefringence measured is much lower than of a typical FLC material. The characteristics of these compounds when compared to a conventional/typical ferroelectric liquid crystalline mixture show that these materials surpass in performance in terms of having a (i) wider temperature range of both SmA* and SmC* phases and (ii) higher switching speed. The layer thickness in SmA* and SmC* is measured using the techniques of (a) small-angle X ray diffraction, and the (b) optical interferometry of free standing smectic films. A comparison of the results is used to determine an exceptionally useful result of the apparent tilt angle as a function of temperature in SmA* without the need of applying the electric field across the cell.
关键词： de Vries characteristics,electro-optic switching,SmA* and SmC* phases,ferroelectric liquid crystalline compounds,birefringence
更新于2025-09-19 17:13:59
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Strain-induced structural phase transition, electric polarization and unusual electric properties in photovoltaic materials CsMI <sub/>3</sub> (M = Pb, Sn)
摘要： The structural phase transition, ferroelectric polarization, and electric properties have been investigated for photovoltaic films CsMI3 (M = Pb, Sn) epitaxially grown along (001) direction based on the density functional theory. The calculated results indicate that the phase diagrams of two epitaxial CsPbI3 and CsSnI3 films are almost identical, except critical transition strains varying slightly. The epitaxial tensile strains induce two ferroelectric phases Pmc21, and Pmn21, while the compressive strains drive two paraelectric phases P212121, P21212. The larger compressive strain enhances the ferroelectric instability in these two films, eventually rendering them another ferroelectric state Pc. Whether CsPbI3 or CsSnI3, the total polarization of Pmn21 phase comes from the main contribution of B-position cations (Pb or Sn), whereas, for Pmc21 phase, the main contributor is the I ion. Moreover, the epitaxial strain effects on antiferrodistortive vector, polarization and band gap of CsMI3 (M = Pb, Sn) are further discussed. Unusual electronic properties under epitaxial strains are also revealed and interpreted.
关键词： structural phase transition,electric properties,photovoltaic films,ferroelectric polarization,epitaxial strain,density functional theory,CsMI3
更新于2025-09-19 17:13:59
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Origin of enhanced piezoelectric properties revealed through electric field driven studies in 0.94(Na <sub/>0.5</sub> Bi <sub/>0.5</sub> TiO <sub/>3</sub> )a??0.06(Ba <sub/>0.85</sub> Ca <sub/>0.15</sub> Ti <sub/>0.9</sub> Zr <sub/>0.1</sub> O <sub/>3</sub> ) ceramics
摘要： A single phase 0.94(Na0.5Bi0.5TiO3)–0.06(Ba0.85Ca0.15Ti0.9Zr0.1O3) solid solution (i.e., BCZT-0.06) is prepared using a conventional solid-state sintering route with enhanced piezo and ferroelectric properties as compared to Na0.5Bi0.5TiO3 (NBT). In the context of understanding the origin of enhanced piezoelectric properties in a BCZT-0.06 specimen, electric field driven studies on different length scales, viz., global, local, and electronic structure, are carried out using x-ray/neutron diffraction, Raman scattering, and UV–Vis spectroscopic techniques. An analysis on different length scales of the electric field-driven BCZT-0.06 specimen displays minimum rhombohedral lattice distortion (δ r), reduced homogeneous lattice strain (δ), octahedral strain (ζ), and pronounced Ti-cation displacement along the polar [111] direction as compared to parent NBT. The enhanced ferro and piezoelectric responses observed in the BCZT-0.06 specimen have been attributed to the ease of non-180° domain re-orientation, domain switching, and domain wall motion due to reduced strain coupled with a polarization extension mechanism.
关键词： ferroelectric properties,electric field driven studies,solid solution,domain re-orientation,piezoelectric properties
更新于2025-09-19 17:13:59
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Controlled polymer crystal/two-dimensional material heterostructures for high-performance photoelectronic applications
摘要： Controlled polymer crystal/two-dimensional material heterostructures for high-performance photoelectronic applications
关键词： epitaxy,epitaxial interaction,semiconducting polymer,graphene,crystal interaction,transition-metal dichalcogenide,ferroelectric polymer,two-dimensional materials
更新于2025-09-19 17:13:59
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Photo-response in 2D metal chalcogenide-ferroelectric oxide heterostructure controlled by spontaneous polarization
摘要： The interplay between free and bound charges in two-dimensional (2D) semiconductor/ferroelectric oxide structures is responsible for the unique opto-electrical properties of these structures. In this study, we vertically combined the 2D layered semiconductors MoS2 (n-type) and WSe2 (p-type) with a ferroelectric oxide (PbTiO3) and found that a ferroelectric polarization induced accumulation or depletion in the layered materials. The heterostructures exhibited polarization-dependent charge distribution and pinched hysteresis. We show that polarization at the interface promoted e?cient charge separation of photo-generated carriers in the 2D layers. Optical control of electrical transport was e?ectively achieved in the MoS2 layers. This study potentially opens up new applications for semiconductor/ferroelectric systems in electronic devices.
关键词： opto-electrical properties,optical control,MoS2,2D semiconductor,ferroelectric oxide,PbTiO3,charge separation,WSe2
更新于2025-09-19 17:13:59
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Improved ferroelectric response of pulsed laser deposited BiFeO <sub/>3</sub> -PbTiO <sub/>3</sub> thin films around morphotropic phase boundary with interfacial PbTiO <sub/>3</sub> buffer layer
摘要： (1 ? x)BiFeO3-xPbTiO3 (BF-xPT) is an interesting material for sensing and actuating devices with large polarization near the morphotropic phase boundary (MPB) (x = 0.30) in the bulk form. However, pulsed laser deposition (PLD) grown (BF-xPT) thin films usually show high electrical leakage and, hence, saturated ferroelectric hysteresis loops are only obtained at subzero temperatures. In this article, we report on high room temperature ferroelectric polarization with saturated hysteresis loops in pulsed laser deposited (BF-xPT) polycrystalline thin films of compositions near the MPB with the use of a thin buffer layer of PbTiO3 (PT). The thin films possessed a perovskite structure with excellent crystallinity and exhibit the presence of a monoclinic (Cm) phase (MA-type) for x = 0.20–0.25 and a mixture of a monoclinic (Cm) phase and a tetragonal (P4mm) phase for x = 0.30–0.35 compositions. The thin films with composition x = 0.25 exhibit a monoclinic phase and yield very large room temperature ferroelectric polarization (2Pr > 80μC/cm2), perhaps the highest room temperature ferroelectric polarization and excellent piezoelectric properties in PLD deposited (BF-xPT) thin films of near-MPB composition. Furthermore, the evolution of ferroelectricity with PT content, studied using room temperature Raman spectroscopy, reveals a correlation with lattice dynamics and stereochemical activity of Bi. Piezoforce domain analysis of the thin films reveals that ferroelectric polarization and electrical leakage in the thin films are intricately related to the type of domains present in the samples, viz., 180°, 109°, 90°, and 71° due to differences in the nature of the domain walls.
关键词： thin films,pulsed laser deposition,PbTiO3 buffer layer,ferroelectric response,BiFeO3-PbTiO3,morphotropic phase boundary
更新于2025-09-19 17:13:59