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![Flexo-photovoltaic effect and light polarization resolved photocurrent mapping. a Schematic showing the electronic process happening at the morphotropic phase boundary. The abbreviation FPV refers the flexo-photovoltaic effect. The number of the red dots denotes the resultant density of nonequilibrium carriers that determines the local photoconduction. b Schematic showing the illumination geometry. c Light polarization dependent photoconduction ratio between R- and T′\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$T\prime$$\end{document}-phases. The solid curve is the fit of the experimental data with Eq. 1. Inset of (b) shows an example of photocurrent mapping with light polarization angle of 150° (left) and its corresponding topography (right). The error bars indicate the standard deviations of photo-conductance ratio between morphotropic phases mapped in a 2 × 0.4 μm² area](publication/334039811/figure/fig5/AS:958959485743105@1605645166247/Flexo-photovoltaic-effect-and-light-polarization-resolved-photocurrent-mapping-a.png)
Flexo-photovoltaic effect and light polarization resolved photocurrent mapping. a Schematic showing the electronic process happening at the morphotropic phase boundary. The abbreviation FPV refers the flexo-photovoltaic effect. The number of the red dots denotes the resultant density of nonequilibrium carriers that determines the local photoconduction. b Schematic showing the illumination geometry. c Light polarization dependent photoconduction ratio between R- and T′\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$T\prime$$\end{document}-phases. The solid curve is the fit of the experimental data with Eq. 1. Inset of (b) shows an example of photocurrent mapping with light polarization angle of 150° (left) and its corresponding topography (right). The error bars indicate the standard deviations of photo-conductance ratio between morphotropic phases mapped in a 2 × 0.4 μm² area
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It has been recently shown that the strain gradient is able to separate the light-excited electron-hole pairs in semiconductors, but how it affects the photoelectric properties of the photo-active materials remains an open question. Here, we demonstrate the critical role of the strain gradient in mediating local photoelectric properties in the stra...
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... At the Schottky interface, a built-in electric field emerges that breaks the inversion symmetry and induces polar structures, resulting in emergent piezoelectricity (17). The piezoelectric effects, acting as strain accommodation, improve interlayered electron transport by preventing significant increases in interfacial resistance caused by structural deformation (36). Figs.S15, S16, and S17 provide computational results based on density function theory (DFT) at the (Fig.S18a-c). ...
Bioelectronic implants with soft mechanics, biocompatibility, and excellent electrical performance enable biomedical implants to record electrophysiological signals and execute interventions within internal organs, promising to revolutionize the diagnosing, monitoring, and treatment of various pathological conditions. However, challenges remain in improving excessive impedance at the bioelectronic-tissue interface and thus the efficacy of electrophysiological signaling and intervention. Here, we devise orbit symmetry breaking in MXene (a low-cost scalability, biocompatible, and conductive 2D layered material, that we refer to as OBXene), that exhibits low bioelectronic-tissue impedance, originating from the out-of-plane charge transfer. Furthermore, the Schottky-induced piezoelectricity stemming from the asymmetric orbital configuration of OBXene facilitates interlayered charge transport in the device. In this study, we report an OBXene-based cardiac patch applied on the left ventricular epicardium of both rodent and porcine models to enable spatiotemporal epicardium mapping and pacing, while coupling the wireless and battery-free operation for long-term real-time recording and closed-loop stimulation.
... In fact, the wide E g of conventional ferroelectrics leads to di culties in absorbing sunlight, and the insulating characteristics lead to severe carrier recombination and low carrier mobility, which are the two major scientific bottlenecks for ferroelectric PV materials to move toward high PCE applications. BiFeO 3 (BFO) has rekindled the research on ferroelectric PV e ect due to its low E g (∼2.6 eV) 5 and stimulated the development of E g engineering, 6,7 nanoscale tip and electrode engineering, 8 strain gradients in mixed phases, 9,10 domain wall engineering, 11,12 and piezoelectric strain and magnetic fields. 13,14 Lead-free inorganic perovskite oxides have an irreplaceable great attraction as representatives of stability, nontoxicity, and economical and easy tunability. ...
... 30 The phase boundaries associated with this strain mismatch often exhibit significant strain gradients, and as a result of the flexoelectric effect, these mixed-phase interfaces showcase intriguing properties. For example, enhanced anisotropic photocurrent, 87 loss of ferroelectric polarization, 88 localized conduction, 89 and multiferroic optical control. 90 investigated the thickness-dependent ferroelectric properties of BTO thin films sandwiched between metallic SrRuO 3 electrodes in a short-circuit configuration. ...
Flexoelectric effect describes the electromechanical coupling between the strain gradient and its internal polarization in all dielectrics. Despite this universality, the resulting flexoelectric field remains small at the macroscopic level. However, in nanosystems, the size-dependent effect of flexoelectricity becomes increasingly significant, leading to a notable flexoelectric field that can strongly influence the material’s physical properties. This review aims to explore the flexoelectric effect specifically at the nanoscale. We achieve this by examining strain gradients generated through two distinct methods: internal inhomogeneous strain and external stimulation. In addition, advanced synthesis techniques are utilized to enhance the properties and functionalities associated with flexoelectricity. Furthermore, we delve into other coupled phenomena observed in thin films, including the coupling and utilization of flexomagnetic and flexophotovoltaic effects. This review presents the latest advancements in these areas and highlights their role in driving further breakthroughs in the field of flexoelectricity.
... For example, Yang et al. demonstrated the generation of photovoltaic currents in centrosymmetric single crystals by introducing strain gradients using an atomic force microscopy (AFM) tip 23 . Chu et al. 24 and Yang et al. 25 observed enhanced photocurrent stemming from a pronounced strain gradient at the mixed-phase interface in BFO, while Guo et al. reported tunable photoconductance in freestanding BFO with controlled strain gradient 26 . The BPVE has also been observed in two-dimensional (2D) MoS 2 created from a strain gradient at the interface 27 . ...
Bulk photovoltaic effect (BPVE) offers an interesting approach to generate a steady photocurrent in a single-phase material under homogeneous illumination, and it has been extensively investigated in ferroelectrics exhibiting spontaneous polarization that breaks inversion symmetry. Flexoelectricity breaks inversion symmetry via strain gradient in the otherwise nonpolar materials, enabling manipulation of ferroelectric order in the absence of electric field. Combining these two effects together, we demonstrate active mechanical control of BPVE in suspended 2-dimensional CuInP 2 S 6 (CIPS) that is ferroelectric yet sensitive to electric field, which enables practical photodetection devices with order of magnitude enhancement in performance. It is found that the suspended CIPS exhibits 20-fold increase in photocurrent, which can be continuously modulated by either mechanical force or light polarization angle. The flexoelectrically engineered photodetection device, activated by air pressure and without any optimization, possesses a responsivity of (2.45 x 10 ⁻² ) A/W and a detectivity of (1.73 x 10 ¹¹ ) Jones, which are superior to ferroelectric-based photodetection and comparable to the commercial Si photodiode.
... Earlier studies [9] have shown that a relatively small deformation of a semiconductor (introducing approximately 10 8 dislocations cm −2 ) could result in a change in the mobility and carrier concentration by an order of magnitude. Many researchers have reported significant improvement in electronic/thermoelectric parameters due to strain induced deformation [10,11]. ...
... Above pair of eqs. (10) and (11) were then brought to 'reduced row echelon form' (rref) and coefficients a 0 and a 1 were determined using the numerical computing open source software Scilab. Now a 1 gives the slope of the least square fitted straight line from which the energy gap E g is calculated for both the samples. ...
The effect of plastic deformation in trigonal direction on galvanomagnetic properties of a pure Bi single crystal is studied systematically in the extensive temperature range 4.2–300K. Basic electronic parameters like carrier concentration and carrier mobility have been calculated and an attempt is made to explain various conduction and scattering mechanisms involved. It is observed that the hole mobility of Bi increases significantly from \(251.6\times {10^3}\) to \(883.3\times {10^3}\)\(\mathrm{{cm}}^2\)\(\mathrm{{Volt}}^{-1}\)\(\mathrm{{s}}^{-1}\) at 4.2K after deformation. This continues to remain higher at all subsequent temperatures. This indicates a greater presence of ‘lighter holes’ implying a shift in the band structure. The energy gap between \(\mathrm{L_C}\) and \(\mathrm{L_V}\) bands is also reported to have increased significantly from 13.79 to 30.53 meV. Further the electron mobility is also found to increase after deformation. The carrier concentration in plastically deformed Bi is almost constant after 70K, followed by a decrease from 230K onwards. An inverse relationship between the mobility and the carrier concentration is seen in the higher temperature region.
... Photocurrent of ferroelectric oxides can be enhanced by two orders of magnitude by the flexoelectric effect corresponding to a giant strain gradient as high as 10 7 /m (27), and the bulk photovoltaic coefficient of MoS 2 sheets is enhanced by orders of magnitude compared to that of most noncentrosymmetric materials under a strain gradient of 10 6 /m (28). Photoconductance of BiFeO 3 films can be effectively mediated by strain gradients (29,30). However, the flexoelectric effect is size dependent and is weak at the macroscale, as is evident from the small flexoelectric coefficients in the range of 10 −5 to 10 −3 C/m for ferroelectrics and ceramics and 10 −10 to 10 −8 C/m for polymers (31). ...
... However, the flexoelectric effect is size dependent and is weak at the macroscale, as is evident from the small flexoelectric coefficients in the range of 10 −5 to 10 −3 C/m for ferroelectrics and ceramics and 10 −10 to 10 −8 C/m for polymers (31). Thus, hereto, the effect has been mostly investigated and used at nano-to microscales where local giant strain gradients can be realized by various ways such as indentation (32)(33)(34), lattice mismatch (27,30,(35)(36)(37)(38), and bending of nano/microscale beams (26,(39)(40)(41)(42). ...
All dielectric materials including ceramics, semiconductors, biomaterials, and polymers have the property of flexoelectricity, which opens a fertile avenue to sensing, actuation, and energy harvesting by a broad range of materials. However, the flexoelectricity of solids is weak at the macroscale. Here, we achieve an ultrahigh flexoelectric effect via a composite foam based on PDMS and CCTO nanoparticles. The mass- and deformability-specific flexoelectricity of the foam exceeds 10,000 times that of the solid matrix under compression, yielding a density-specific equivalent piezoelectric coefficient 120 times that of PZT. The flexoelectricity output remains stable in 1,000,000 deformation cycles, and a portable sample can power LEDs and charge mobile phones and Bluetooth headsets. Our work provides a route to exploiting flexible and light-weight materials with highly sensitive omnidirectional electromechanical coupling that have applications in sensing, actuation, and scalable energy harvesting.
... In 2019, the lattice mismatch in the morphotropic phase boundary (MPB) was investigated in an epitaxial BiFeO 3 film on a LaAlO 3 substrate, which featured a coexisting monoclinic phase and rhombohedral phase. A large lattice mismatch around the MPB introduced a strain gradient of 10 7 m − 1 [6]. b) Applying a local force via a mechanically loaded scanning probe on the ceramic thin film. ...
Ferroelectric memories show great potential in applications of portable electronics due to low power consumption, high reliability and fast response speed. Therefore, non-destructive readout of ferroelectric memories using the ferroelectric photovoltaic effect attracted tremendous research attention. In this investigation, flexoelectric-enhanced photovoltaic effect (FPV effect) were systematically investigated in curved 3D-printed BaTiO3/PVDF composite films. In the bending process, a strain gradient field was formed between the BaTiO3 (BTO) particles, which led to a relatively large flexoelectric effect. Compared with that of pristine PVDF, the flexoelectric coefficient of BTO/PVDF-15 (15% BTO) was increased 3.7-fold to 2.65 × 10⁻⁹ C/m. Furthermore, we found that the photovoltaic current Ipv of the BTO/PVDF-15 (15% BTO) composite film increased by 3.4 times compared with the pristine PVDF film at the same curvature. This is mainly attributed to the FPV effect. In addition, “polarization channels” were found for the first time inside nanocomposite materials using the flexoelectricity effect through 2D phase-field simulations, and the channels can be artificially controlled by simply bending the film. Most importantly, the BTO/PVDF-based composite film was designed as flexible ferroelectric memories. We demonstrated for the first time that the intensity difference of the signal for 0 and 1 of the BTO/PVDF-based memories were more than 10 times, which can be read directly using a laser. This investigation shows great promise that flexoelectricity in piezoelectric polymer nanocomposite can greatly benefit the nondestructive readout of ferroelectric memory devices.
... Matsuo et al. showed a study for improving photovoltaic performance without disturbing spontaneous polarization [57]. In Fig. 5c1 & 5c2, [58]] relationship between photocurrent and R/T mixed phase regions have been shown. It is also revealed that the photocurrent is increased whereas, T-phase shows decrease in photoconductivity as shown in figure (5c3, [58]). ...
... In Fig. 5c1 & 5c2, [58]] relationship between photocurrent and R/T mixed phase regions have been shown. It is also revealed that the photocurrent is increased whereas, T-phase shows decrease in photoconductivity as shown in figure (5c3, [58]). Yang et al., in his study, used small BFO films to demonstrate the role of strain gradient in regulating photoelectric structures [58]. ...
... It is also revealed that the photocurrent is increased whereas, T-phase shows decrease in photoconductivity as shown in figure (5c3, [58]). Yang et al., in his study, used small BFO films to demonstrate the role of strain gradient in regulating photoelectric structures [58]. The effect of temperature in the BFO photocurrent device was also studied [59]. ...
Fuel crisis and atmospheric pollution have been major environmental issues from the advent of the nuclear era of 1945. Photocatalysis for water splitting and organic contaminant degradation in presence of sunlight is a promising and recently in-trend for solving current environmental problems. Photocatalytic oxidation offers distinct advantages such as its extensive applicability of total mineralization of organic compounds without any secondary pollution. Bismuth Ferrite (BiFeO3) and its doped materials have gained a lot of attention nowadays due to its very narrow band gap (≈2.1 eV), recycling nature, coexistence of magnetic and ferroelectric properties and distinctive crystal structure. Due to these elaborated properties, Bismuth Ferrite emerges as an interesting material as a photocatalyst. The focus of this article is to summarize BFO photocatalytic properties and how can it be used to remediate air pollutants and water pollutants multiple times. This review also broadly discusses about BiFeO3 as a visible light photocatalyst and its present shape of work, research gaps and future scope.
... The electronic re-construction due to the presence of strain gradient (flexoelectric field) at DWs allows the photoexcitation process even from the below bandgap excitation. The strain-gradient induced local asymmetric field (Es) effectively separates out the photo-excited carriers and hence, has angular dependence as a function of incident light polarization [52,53,54,55,56] . The photo-excited carriers screen the local polarization components, and renormalize the local electric field or strain-gradient [57] . ...
The sensitivity of ferroelectric domain walls to external stimuli makes them functional entities in nanoelectronic devices. Specifically, optically driven domain reconfiguration with in-plane polarization is advantageous and thus highly sought. Here, we show the existence of in-plane polarized sub-domains imitating a single domain state and reversible optical control of its domain wall movement in a single-crystal of ferroelectric BaTiO3. Similar optical control in the domain configuration of non-polar ferroelastic material indicates long-range ferroelectric polarization is not essential for the optical control of domain wall movement. Instead, flexoelectricity is found to be an essential ingredient for the optical control of the domain configuration and hence, ferroelastic materials would be another possible candidate for nanoelectronic device applications.
... Fig. S3a presents the UV-Vis absorbance spectrum of the BNT ceramics, showing a sharp absorption edge at about 420 nm. A Tauc plot obtained according to the absorption spectrum, shows that the bandgap of the BNT ceramic is approximately 2.95 eV (Fig. S3b), which is consistent with the bandgap (2.94 eV) reported by Parija et al. [22] XRD patterns ( Fig. S4) indicate that the fabricated BNT ceramics maintains a single-phase perovskite structure with rhombohedral symmetry as the temperature varies from 183 K to 373 K [23,24]. Fig. S5 presents the temperature-related dielectric property of BNT ceramics at 10 2 -10 4 Hz. ...
The photocurrent generated by ferroelectric materials via the photovoltaic effect has latent applications in opto-electronic devices due to the introduction of a polarization-induced charge carrier separation and transport, which is absent in semiconducting p-n junctions. However, the precise mechanism of photocurrent production in photoelectric devices by a range of ferroelectric materials remains a topic of continued interest. Here we report a significant enhancement in the photocurrent of a ferroelectric Bi0.5Na0.5TiO3-based photoelectric device by ferro-pyro-phototronic effect. When compared with the generated photocurrent under illumination alone, the peak and platform photocurrents induced by the simultaneous use of both light and heating can be increased by 131% and 57%, respectively. The increase in photocurrent is found to increase with temperature, where the mechanism of enhancement is associated with the increase in pyroelectric coefficient, photoexcited carrier concentration and carrier mobility at higher operating temperatures. These factors also lead to a rapid response time of 84.2 ms. This work provides guidelines for photocurrent promotion in ferroelectric devices, pushing forward the potential applications of ferroelectric materials for self-powered photodetectors.
