The lead-free sodium bismuth titanate (BNT) system has been extensively investigated in the past decade due to its multi-functional electro-active properties. Here, we present a comprehensive review ...that encompasses the fundamentals and state-of-the-art in the development of BNT-based ceramics, with attention to the underlying composition, microstructure, and macroscopic properties. The phase structure, phase transitions, and relaxor characteristics of BNT and BNT-based solid solutions are described carefully, with a series of proposed phase diagrams. The attractive functional properties of BNT-based ceramics include piezoelectricity, electric-field-induced strain, and energy storage performance for applications in sensors, actuators, and dielectric capacitors. The focus of this review is on the microscopic origin of the macroscopic behavior, the proposed strategies for optimization of functional properties, and current challenges. Moreover, the potential applications of BNT-based ceramics in the areas of electrocaloric, oxide-ion conduction, and luminescence are briefly introduced. Finally, future perspectives are provided to highlight new and emerging research directions in this growing area.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The evolution of electrical properties with an electric field (E) was compared between single‐phase BT ceramic and phase‐coexistence BT‐based (BTS–0.15BCT) ceramic. The dielectric, ferroelectric, ...piezoelectric, and strain properties are all found to be electric field‐dependent, especially for BTS–0.15BCT ceramic with small domains and easy polarization rotation induced by phase coexistence. High ferroelectric and strain properties are obtained in this ceramic because sufficient domain switching can easily be achieved. The high dielectric constant can be further elevated after poling this ceramic due to the E‐induced multiphase transitions. Dynamic piezoelectric measurement reveals that the dynamic piezoelectricity can reach to ∼740 pC/N, which is much higher than the static value (∼620 pC/N) of poled BTS–0.15BCT ceramic. However, the converse piezoelectric coefficient will decrease at high E, because of the quick decrease in dynamic dielectric response caused by clamped polarization at high E. All the results demonstrate that phase‐coexistence BT‐based ceramic shows electric field‐related properties due to the soft structure, whereas it cannot be observed in BT ceramic with stable phase structure and large domains. This work reveals the evolution difference and structure origin of electrical properties in BT‐based piezoceramics with different phase structures.
The evolution of electrical properties under different electric field was compared between single‐phase BT ceramic and phase‐coexistence BT‐based ceramic. The dielectric, ferroelectric, piezoelectric, and strain properties are all electric field‐dependent in later ceramic, which exhibits the ultrahigh dynamic piezoelectric response of ∼740 pC/N and dielectric constant of ∼6800, being higher than the static/unpoled properties. The structure origin is attributed to the soft structure and polarization state and quite small domains induced by phase coexistence.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
In this work, the random electric fields are constructed in the hard PZT ceramics by adding the ZnO particles as a secondary phase to tune the piezoelectric properties and losses. It is found that ...the internal bias electric field existing in the hard PZT ceramics has been tuned successfully by the random electric fields and its value reduces with the increased ZnO content. As a consequence, the piezoelectric constant d33 reaches up to 483 pC/N in the PZT/0.75 wt%ZnO composite, which is much higher than that of the hard PZT matrix. In the meantime, the electromechanical quality factor Qm, dielectric loss tan δ, and Curie temperature TC for this composite are about 1109, 0.55%, and 279°C, respectively. The promoted d33 is attributed to the small domain size and reduced internal bias electric field, whereas the low losses (large Qm and low tan δ) can be put down to the still existing nonzero internal bias electric field.
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Mechanical energy harvesting using triboelectric nanogenerators is a highly desirable and sustainable method for the reliable power supply of widely distributed electronics in the new era; however, ...its practical viability is seriously challenged by the limited performance because of the inevitable side-discharge and low Coulombic-efficiency issues arising from electrostatic breakdown. Here, we report an important progress on these fundamental problems that the spontaneously established reverse electric field between the electrode and triboelectric layer can restrict the side-discharge problem in triboelectric nanogenerators. The demonstration employed by direct-current triboelectric nanogenerators leads to a high Coulombic efficiency (increased from 28.2% to 94.8%) and substantial enhancement of output power. More importantly, we demonstrate this strategy is universal for other mode triboelectric nanogenerators, and a record-high average power density of 6.15 W m
Hz
is realized. Furthermore, Coulombic efficiency is verified as a new figure-of-merit to quantitatively evaluate the practical performance of triboelectric nanogenerators.
Efficient bifunctional electrocatalysts for hydrogen and oxygen evolution reactions are key to water electrolysis. Herein, we report a built‐in electric field (BEF) strategy to fabricate ...heterogeneous nickel phosphide‐cobalt nanowire arrays grown on carbon fiber paper (Ni2P‐CoCH/CFP) with large work function difference (ΔΦ) as bifunctional electrocatalysts for overall water splitting. Impressively, Ni2P‐CoCH/CFP exhibits a remarkable catalytic activity for hydrogen and oxygen evolution reactions to obtain 10 mA cm−2, respectively. Moreover, the assembled lab‐scale electrolyzer driven by an AAA battery delivers excellent stability after 50 h electrocatalysis with a 100 % faradic efficiency. Computational calculations combining with experiments reveal the interface‐induced electric field effect facilitates asymmetrical charge distributions, thereby regulating the adsorption/desorption of the intermediates during reactions. This work offers an avenue to rationally design high‐performance heterogeneous electrocatalysts.
By proposing and fabricating Ni2P‐CoCH heterostructure with large ΔΦ as a model catalyst for overall alkaline water electrolysis, the introduction of a strong built‐in electric field (BEF) is successfully realized to create the asymmetrical charge distributions on catalyst surfaces. The negative charge‐enriched Ni2P and positive charge‐enriched CoCH as active sites separately achieve high hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activities.
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•Experiments on the influence of electric field on the melting of n-octadecane inside a macrocapsule are conducted.•The electric field may accelerate or hinder the melting depending on the relative ...temperature of the electrode that the voltage is applied.•The Coulomb force rather than the dielectric force plays the vital role.•In our experiments, free charges are generated due to the conduction mechanism.
Experiments on the melting characteristics of n-octadecane with electric field inside a cavity are carried out. The classical differentially heated cavity is considered to explore the effect of electric field on solid-liquid phase change heat transfer. The influence of the applied voltage's polarity and magnitude on the melting process of n-octadecane is investigated. The dynamic evolution of the liquid fraction and solid-liquid interface positions with melting time are reported. The velocity fields and electric current-voltage curves are also presented for understanding the physical mechanism. Results show that Coulomb force plays the central role in affecting the melting heat transfer process. The electric field would hinder or accelerate the melting process depending on the strength of electric field. When the applied voltage set to the right wall that is cold is larger than 10.0kV, the electric field would obviously accelerate the melting process. For a cavity with the length of 40.0 mm, the charge injection is hardly taken place when the maximum DC voltage of 20.0kV is applied, so the free charge carriers are mainly generated by conduction mechanism.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
For calibration of the environmental monitoring field meters, a reference standard of electric field strength based on parallel plates is established in the Primary electromagnetic laboratory FER-PEL ...in Croatia. The plate system incorporates guard ring electrodes with a set potential distribution to improve field uniformity within the center calibration volume. In addition, the concept of the Kelvin guard-ring electrode applied to one of the plates allows the measurement of the displacement current through the guarded plate system. The reference electric field strength is derived from the nondimensional field distribution factor, calculated from the ratios of the system's quantities, and the measured voltage and capacitance of the plates. The elaborate uncertainty budget confirms expanded uncertainty of 1.2 % for generating low-frequency reference fields up to 20 kV/m, with exclusively electrical traceability.
Inferior contact interface and low charge transfer efficiency seriously restrict the performance of heterojunctions. Herein, chemically bonded α‐Fe2O3/Bi4MO8Cl (M=Nb, Ta) dot‐on‐plate Z‐scheme ...junctions with strong internal electric field are crafted by an in situ growth route. Experimental and theoretical results demonstrate that the internal electric field provides a powerful driving force for vectorial migration of photocharges between Bi4MO8Cl and α‐Fe2O3, and the interfacial Fe−O bond not only serves as an atomic‐level charge flow highway but also lowers the charge transfer energy barrier, thereby accelerating Z‐scheme charge transfer and realizing effective spatial charge separation. Impressively, α‐Fe2O3/Bi4MO8Cl manifests a significantly improved photocatalytic activity for selective oxidation of aromatic alcohols into aldehydes (Con. ≥92 %, Sel. ≥96 %), with a performance improvement of one to two orders of magnitude. This work presents atomic‐level insight into interfacial charge flow steering.
Chemically bonded α‐Fe2O3/Bi4MO8Cl (M=Nb, Ta) dot‐on‐plate Z‐scheme junctions with strong internal electric field are crafted by an in situ growth route, which provides a powerful driving force, abundant atomic‐level charge flow highways and a decreased energy barrier for directional migration and spatial separation of photocharges, greatly improving the photocatalytic activity for selective photo‐oxidation of aromatic alcohols.
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•Nanosized CdS decorated TiO2@BaTiO3 core–shell composite was successfully synthesized.•The designed composite removes the shielding effect toward the polarized electric field.•A ...permanent built-in electric field is formed in BaTiO3 layer without applied mechanical stress.•The photoexcited charge carriers realize completely spatial separation.•This composite shows an excellent photocatalytic hydrogen activity.
Ferroelectrics have the advantage of spatially separating the photogenerated charge carriers via the spontaneous polarized electric field, although the strength of the polarized electric field may suffer from the influence of the electrostatic shielding effect, which could reduce the charge carrier separation without mechanical stress. Herein, we developed a novel CdS decorated TiO2@BaTiO3 core–shell nanocomposite, where the optimal ratio of TiO2, BaTiO3 and CdS are 53.43, 37.37 and 9.20 wt%, respectively, for the best photocatalytic activity. The TiO2@BaTiO3/CdS nanocomposite reported in this work offers a persistent electric field in the ferroelectric BaTiO3 shell, due to the limited shielding effect in an asymmetrically polarized field. With the built-in electric field as the driving force, the photogenerated electrons and holes flowed into the CdS surface and the TiO2 core, respectively, with improved charge separation to participate in water-splitting reactions. The measured charge carrier lifetime of TiO2@BaTiO3/CdS nanocomposite via transient fluorescence spectrum is 0.42 ns, which is much longer than the TiO2 (0.25 ns) and TiO2@BaTiO3 (0.31 ns) samples. The TiO2@BaTiO3/CdS nanocomposite shows an enhanced photocatalytic hydrogen evolution rate of 13.22 mmol/g∙h under visible light illumination with an AQE of 52.50 % at 405 nm monochromatic light. This is much better than their components and binary composites, including TiO2/Pt (0.63 mmol/g∙h), CdS (1.23 mmol/g∙h), TiO2@BaTiO3 (0.03 mmol/g∙h), TiO2/CdS (0.53 mmol/g∙h), and BaTiO3/CdS (2.62 mmol/g∙h). This work provides an effective strategy for the construction of a ferroelectric photocatalyst with much-improved charge separation by the permanent internal electric field.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
We present space‐ and ground‐based multi‐instrument observations demonstrating the impact of the 2022 Tonga volcanic eruption on dayside equatorial electrodynamics. A strong counter electrojet (CEJ) ...was observed by Swarm and ground‐based magnetometers on 15 January after the Tonga eruption and during the recovery phase of a moderate geomagnetic storm. Swarm also observed an enhanced equatorial electrojet (EEJ) preceding the CEJ in the previous orbit. The observed EEJ and CEJ exhibited complex spatiotemporal variations. We combine them with the Ionospheric Connection Explorer neutral wind measurements to disentangle the potential mechanisms. Our analysis indicates that the geomagnetic storm had minimal impact; instead, a large‐scale atmospheric disturbance propagating eastward from the Tonga eruption site was the most likely driver for the observed intensification and directional reversal of the equatorial electrojet. The CEJ was associated with strong eastward zonal winds in the E‐region ionosphere, as a direct response to the lower atmosphere forcing.
Plain Language Summary
The Earth's E‐region ionosphere (∼100–150 km altitude) consists of both ionized and neutral gasses, and the two components are coupled through ion‐neutral collisions. The state of this region is closely influenced by neutral atmospheric activities from the lower atmosphere and the variability of the solar drivers. On 15 January 2022, the Tonga volcano had a massive eruption and injected an enormous amount of mass and energy into the atmosphere causing disturbances in the E‐region ionosphere or even higher. There was also a moderate geomagnetic storm that started 1 day before the eruption and ended days after. These conditions offer a unique opportunity to understand the different roles they play in controlling the ionosphere. Coordinated observations, including the atmosphere, ionosphere, and magnetosphere, were made from both space and on the ground during this event. We analyzed the magnetic field and neutral wind data and found that a large‐scale atmospheric disturbance generated by the volcano eruption was responsible for the observed directional reversal of the dayside equatorial electric field and electric current.
Key Points
Space‐ and ground‐based observations reveal dramatic equatorial electrojet variations caused by the Tonga volcanic eruption
Strong eastward turning of atmospheric zonal winds in the E‐region is responsible for the directional reversal of the equatorial electrojet
The observed complex spatiotemporal variations can be explained by a large‐scale disturbance propagating eastward from the eruption site
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