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Charge separation is critical for achieving efficient solar-to-hydrogen conversion, whereas piezoelectric-enhanced photoelectrochemical (PEC) systems can effectively modulate band bending and charge migration. Herein, we design an n-TiO2/BaTiO3/p-TiO2 (TBTm) heterojunction in which the piezoelectric BaTiO3 layer is sandwiched between n-TiO2 and p-TiO2. The built-in electric field of TBTm can provide a strong driving force to accelerate carrier separation and prolong carrier lifetime. Consequently, the TBT3 achieves a prominent photocurrent density, as high as 2.13 mA cm−2 at 1.23 V versus reversible hydrogen electrode (RHE), which is 2.4- and 1.5-times higher than TiO2 and TiO2–BaTiO3 heterojunction, respectively. Driven by mechanical deformation, the induced dipole polarization can further regulate built-in electric fields, and the piezoelectric photocurrent density of TBT3-800 is 2.84 times higher than TiO2 at 1.23 V vs. RHE due to the construction of piezoelectric-heterostructures. This work provides a piezoelectric polarization strategy for modulating the built-in electric field of heterojunction for PEC system.

Charge separation is critical for achieving efficient solar-to-hydrogen conversion, whereas piezoelectric-enhanced photoelectrochemical (PEC) systems can effectively modulate band bending and charge migration. Herein, we design an n-TiO2/BaTiO3/p-TiO2 (TBTm) heterojunction in which the piezoelectric BaTiO3 layer is sandwiched between n-TiO2 and p-TiO2. The built-in electric field of TBTm can provide a strong driving force to accelerate carrier separation and prolong carrier lifetime. Consequently, the TBT3 achieves a prominent photocurrent density, as high as 2.13 mA cm2 at 1.23 V versus reversible hydrogen electrode (RHE), which is 2.4- and 1.5-times higher than TiO2 and TiO2-- BaTiO3 heterojunction, respectively. Driven by mechanical deformation, the induced dipole polarization can further regulate built-in electric fields, and the piezoelectric photocurrent density of TBT3-800 is 2.84 times higher than TiO2 at 1.23 V vs. RHE due to the construction of piezoelectric-heterostructures. This work provides a piezoelectric polarization strategy for modulating the built-in electric field of heterojunction for PEC system. [ABSTRACT FROM AUTHOR]

Manipulating the catalyst body and surface photogenerated charge separation is significant in expanding research in the field of photoelectrochemical water splitting. This paper introduces a certain amount of Bi-vacancies at the BiVO4 photoanode by in-situ photoreduction and makes rational use of polarization field engineering to promote the separation of surface photogenerated carriers. Focusing on comparing the photoelectrochemistry (PEC) performance of BiVO4 with different concentrations of Bi-vacancies under piezoelectric polarization field. At 1.23 V vs. RHE, the photocurrent density of the best sample is 0.147 mA/cm2, which is 1.8 times higher than that of BiVO4. In addition, the photocurrent density reached 0.162 mA/cm2 under ultrasonic conditions. The presence of a moderate amount of Bi-vacancies provides a large number of active sites, which lowers the potential barrier for redox reactions thereby reducing the resistance to electron leaps, decreasing the forbidden bandwidth and increasing the light absorption range. The piezoelectric polarization field is triggered by ultrasonic conditions, and the cavitation bubbles are ruptured by ultrasonic vibrations, generating a large amount of charge involved in the water splitting reaction. The presence of surface vacancies makes the piezoelectric polarization easier to be triggered, and the enhanced built-in piezoelectric field acts as a driving force to improve the interfacial separation and transport efficiency of photogenerated carriers, which effectively improves the PEC performance. This work provides a new and scientifically sound idea for the combined use of vacancy defect engineering and piezoelectric effect in the field of PEC splitting water. [ABSTRACT FROM AUTHOR]

Development of metal oxide semiconductors‐based methane sensors with good response and low power consumption is one of the major challenges to realize the real‐time monitoring of methane leakage. In this work, a self‐assembled mulberry‐like ZnO/SnO2 hierarchical structure is constructed by a two‐step hydrothermal method. The resultant sensor works at room temperature with excellent response of ~56.1% to 2000 ppm CH4 at 55% relative humidity. It is found that the strain induced at the ZnO/SnO2 interface greatly enhances the piezoelectric polarization on the ZnO surface and that the band bending results in the accumulation of chemically adsorbed O2− ions close to the interface, leading to significant improvement in the sensing performance of the methane gas sensor at room temperature. [ABSTRACT FROM AUTHOR]

A piezo-photocatalytic system integrating dual electric fields constructed by weak force-driven piezoelectric polarization and Z-scheme junction is developed in 0D/2D α-Fe 2 O 3 /Bi 2 WO 6 , which shows accelerated migration of bulk and interfacial photoexcited carriers and strong visible light response, resulting in a superb tetracycline hydrochloride photodegradation efficiency. [Display omitted] • 0D/2D α-Fe 2 O 3 /Bi 2 WO 6 Z-scheme junction was synthesized. • Water flow-driven piezoelectric polarization field was introduced into photocatalysis. • Piezoelectric filed and internal electric field increase separation efficiency of charges. • FO/BWO exhibits excellent piezo-photocatalytic performance for TH degradation. Photocatalysis shows huge potential in environmental purification, but suffers from fast photocharge recombination and finite photoabsorption. Piezoelectric polarization is perceived as a promising approach to drive charge separation, but it always relies on the energy-guzzling ultrasonic vibration. Herein, a piezo-photocatalytic system integrating dual electric fields constructed by weak force-driven piezoelectric polarization and Z-scheme junction is developed in 0D/2D α-Fe 2 O 3 /Bi 2 WO 6. The introduction of low-frequency water flow-induced piezoelectric polarization field accelerates the migration of bulk photoexcited carriers of polar Bi 2 WO 6 , and forming Z-scheme junction with intimate interface guarantees the spatial separation of interfacial charges and strong visible light response. Benefiting from these merits, water flow-triggered α-Fe 2 O 3 /Bi 2 WO 6 delivers a superb tetracycline hydrochloride photodegradation efficiency of 82% within 20 min, which outperforms related piezo-photocatalysts in previous reports, even those driven by high-frequency ultrasound. KPFM and DFT calculations provide forceful evidence for the Z-scheme transfer pathway between α-Fe 2 O 3 and Bi 2 WO 6. Additionally, the synergetic effect of constructing the Z-scheme junction and introducing piezoelectric polarization is well confirmed by PFM, COMSOL simulation, ESR and photoelectrochemical characterization. This work offers a novel strategy to design the piezo-photocatalytic system and maybe realize the in-situ treatment of sewage taking full advantage of hydrodynamic characteristics. [ABSTRACT FROM AUTHOR]

The serious separation of electron–hole wavefunctions, which is caused by the built-in electric field, prevents electron–hole radiative recombination in quantum wells (QWs) in high-In-content InGaN-based red light-emitting diodes (LEDs). Here, we propose a staggered structure that inserts an ultrathin InN layer in the single quantum well (SQW) to reduce the piezoelectric polarization and suppress the quantum confined Stark effect (QCSE). We have numerically simulated the effects of SQW with the InN insertion layer (IL) on the energy band structure and electron–hole wavefunctions of the red LED. Owing to alleviated piezoelectric polarization and improved overlaps of electron–hole wavefunctions, the simulation results have revealed that the internal quantum well (IQE) of the red LED with InN IL exhibits 42% higher than that of the red LED with a square-shaped QW (SSQW) at 60 A/cm2, and the efficiency droop ratio of red LED with InN IL is 48% lower than that of red LEDs with SSQW. Furthermore, we have found that the position of InN IL can affect the energy states of carriers, which has a great influence on the IQE and peak emission wavelength of red LEDs. [ABSTRACT FROM AUTHOR]

The experimental data on orientation relationships for halide vapor phase epitaxy (HVPE) κ-Ga2O3 film grown on (0001) α-Al2O3 substrate and the theoretical model that describes growth orientation dependences of stress–strain state and piezoelectric polarization in κ-(AlxGa1-x)2O3 films with orthorhombic crystal structure grown on α-Al2O3 and κ-Al2O3 substrates are presented. Two possibilities for variation in films growth orientation for κ-Ga2O3/α-Al2O3 and κ-(AlxGa1–x)2O3/κ-Al2O3 heterostructures with inclination axes about either [100] or [010] crystallographic directions are considered. The changes in elastic strain field and piezoelectric polarization in the film caused by the differences in values of lattice parameters, elastic, and piezoelectric constants are demonstrated. The growth planes for κ-Ga2O3/α-Al2O3 and κ-(AlxGa1–x)2O3/κ-Al2O3 heterostructures that are characterized by low internal stresses and low or zero values of piezoelectric polarization are found.

Developing efficient piezocatalytic systems for two‐electron water splitting (TEWS) with producing H2 and H2O2 shows great promise to meet the industrial demand. Herein, Ag single atoms (SAs) and clusters are co‐anchored on carbon nitride (AgSA+C−CN) to serve as the multifunctional sites for efficient TEWS. The Ag SAs enhance the in‐plane piezoelectric polarization of CN that is intimately modulated by the atomic coordination induced charge redistribution, and Ag clusters afford strong interfacial electric field to remarkably promote the out‐of‐plane migration of piezoelectrons from CN. Moreover, AgSA+C−CN yields a larger piezoresistive effect that elevates carrier mobility under strain. Consequently, a superior H2 and H2O2 evolution rate of 7.90 mmol g−1 h−1 and 5.84 mmol g−1 h−1 is delivered by AgSA+C−CN, respectively, far exceeding that of the previously reported piezocatalysts. This work not only presents the SAs decoration as an available polarization enhancement strategy, but also sheds light on the superiority of multi‐sites engineering in piezocatalysis. [ABSTRACT FROM AUTHOR]

• Weak water flow-driven piezoelectric polarization and heterojunction co-contribute to piezo-photocatalytic CTC degradation. • The optimized ZnS/Fe 2 O 3 exhibits a piezo-photocatalytic CTC degradation rate of 73.2 % within 20 min. • The combination of type-I junction and piezo-polarization endows ZnS/Fe 2 O 3 with excellent charges separation ability. Photocatalysis is considered to be a sustainable and less polluting environmental purification technology, however, the limited photogenerated charge separation efficiency and light absorption hinder its large-scale application. Encouragingly, piezocatalysis is proposed as an emerging and appealing strategy to drive the migration and separation of photoinduced carriers. Nevertheless, the source of piezocatalysis is usually derived from high energy-consuming ultrasonic vibration. Herein, we realize superior piezo-photocatalytic chlortetracycline hydrochloride degradation performance stimulated by low-frequency water flow-driven piezoelectric polarization of I-type ZnS/Fe 2 O 3 junction. The integration of Fe 2 O 3 is beneficial to extend the light absorption from ultraviolet region to visible range and boost the charge separation efficiency of ZnS/Fe 2 O 3. Meanwhile, the piezoelectric polarization triggered by weak water flow further promotes the directional separation of photogenerated carriers. With all these merits, the optimized ZnS/Fe 2 O 3 shows a piezo-photocatalytic chlortetracycline hydrochloride (CTC) degradation rate of 73.2 % within 20 min, which is 2.8 and 2.1 times that of Fe 2 O 3 and ZnS, respectively, and 17.4-fold and 1.1-fold that of single stirring and light, respectively. This work provides a feasible guidance for designing efficient piezo-photocatalysts for in-situ purification of wastewater in natural environmental with effective visible light responsiveness and sensitivity to weak mechanical stress. [ABSTRACT FROM AUTHOR]

Profiting from the piezoelectric effect, the CuInS2-BiFeO3 S-scheme heterojunction with eliminated interface shielding effect facilitates carrier separation and exhibits an excellent piezo-photocatalytic H2 evolution performance driven by the synergy of piezoelectric field and S-scheme built-in electric field. [Display omitted] • CuInS 2 -BiFeO 3 is constructed via a hydrothermal method with electrostatic self-assembly strategy. • Piezoelectric field eliminates the interface shielding effect within S-scheme heterojunction. • Synergistic utilization of built-in field and piezo-polarization field exhibits superior photocatalytic performance. Eliminating the interface shielding effect within step-scheme (S-scheme) heterojunctions which can attenuate the separation driving force of built-in electric field plays a vital role in enhancing the photocatalytic performance. Herein, an extra driving force induced by piezoelectric field is introduced to mitigate such predicament in S-scheme, thereby facilitating the charge separation. Specifically, the piezoelectric CuInS 2 -BiFeO 3 S-scheme heterojunction which with powerful piezoelectric field endowed by the piezoelectric BiFeO 3 is constructed via a facile electrostatic self-assembly strategy and served as the touchstone to verify that hypothesis. The direction of built-in field between the heterojunction interface that is orienting from CuInS 2 to BiFeO 3 has been confirmed by in-situ X-ray photoelectron spectroscopy and electron paramagnetic resonance. Furthermore, the obviously piezo-field at the interface of CuInS 2 -BiFeO 3 which can tilt energy band to enhance the built-in field under external force is also revealed by piezoresponse force microscopy. Consequently, benefiting from the highly-efficient charge separation offered by the synergy of piezoelectric field and S-scheme built-in electric field, a remarkably H 2 production rate of 1465.1 µmol/g is achieved under simultaneous visible light and ultrasonic vibration irradiation. This work sheds light on the role of external field in enhancing the efficient separation of carriers in S-scheme heterojunctions. [ABSTRACT FROM AUTHOR]

The article is devoted to solving the problem of ensuring high piezoactivity of composite piezoceramic transformers, in which the component parts are connected by soldering. The existing connection features have been analysed for the elements of composite piezoceramic transformers and the results have shown that during soldering the piezoceramic elements are exposed to thermal shock leading to depolarization of piezoceramics and deterioration of its piezoelectric properties. Diminution of temperature depolarizing effect is possible using low-temperature solders with a high tin content. However, in this case, the diffusion process of the electrode material of the piezoelectric element into the solder increases and the mechanical connection strength decreases. To eliminate these negative phenomena and solve the problem, a new method has been developed for connecting elements of composite piezoceramic transformers by soldering, where a polarizing voltage is applied to the composite piezoceramic transformer when heating and cooling, which prevents depolarization of the domain structure of piezoceramic elements. At the same time, high temperature ensures that polarization is carried out at lower values of the electric tension, and a more mobile domain structure after polarization has a lower level of coercive forces and, accordingly, a greater stability of parameters ov er time. Experimental verification has shown that the relative resonance gap increases by 6 % with a decrease in the dispersion of this value by 12 %, which indicates an increase in piezoactivity and stability of the characteristics of composite piezoceramic transformers manufactured using the solution above.

The serious separation of electron–hole wavefunctions, which is caused by the built-in electric field, prevents electron–hole radiative recombination in quantum wells (QWs) in high-In-content InGaN-based red light-emitting diodes (LEDs). Here, we propose a staggered structure that inserts an ultrathin InN layer in the single quantum well (SQW) to reduce the piezoelectric polarization and suppress the quantum confined Stark effect (QCSE). We have numerically simulated the effects of SQW with the InN insertion layer (IL) on the energy band structure and electron–hole wavefunctions of the red LED. Owing to alleviated piezoelectric polarization and improved overlaps of electron–hole wavefunctions, the simulation results have revealed that the internal quantum well (IQE) of the red LED with InN IL exhibits 42% higher than that of the red LED with a square-shaped QW (SSQW) at 60 A/cm2, and the efficiency droop ratio of red LED with InN IL is 48% lower than that of red LEDs with SSQW. Furthermore, we have found that the position of InN IL can affect the energy states of carriers, which has a great influence on the IQE and peak emission wavelength of red LEDs.

Piezoelectric semiconductors have emerged as redox catalysts, and challenges include effective conversion of mechanical energy to piezoelectric polarization and achieving high catalytic activity. The catalytic activity can be enhanced by simultaneous irradiation of ultrasound and light, but the existing piezoelectric semiconductors have trouble absorbing visible light. A piezoelectric catalyst is designed and tested for the generation of hydrogen peroxide (H2O2). It is based on Nb‐doped tetragonal BaTiO3 (BaTiO3:Nb) and is sensitized by carbon quantum dots (CDs). The photosensitizer injects electrons into the conduction band of the semiconductor, while the piezoelectric polarization directed electrons to the semiconductor surface, allowing for a high‐rate generation of H2O2. The piezoelectric polarization field restricts the recombination of photoinduced electron–hole pairs. A production rate of 1360 µmol gcatalyst−1 h−1 of H2O2 is achieved under visible light and ultrasound co‐irradiation. Individual piezo‐ and photocatalysis yielded lower production rates. Furthermore, the CDs enhance the piezocatalytic activity of the BaTiO3:Nb. It is noted that moderating the piezoelectricity of BaTiO3:Nb via microstructure modulation influences the piezophotocatalytic activity. This work shows a new methodology for synthesizing H2O2 by using visible light and mechanical energy. [ABSTRACT FROM AUTHOR]

Abstract Piezoelectric semiconductors have emerged as redox catalysts, and challenges include effective conversion of mechanical energy to piezoelectric polarization and achieving high catalytic activity. The catalytic activity can be enhanced by simultaneous irradiation of ultrasound and light, but the existing piezoelectric semiconductors have trouble absorbing visible light. A piezoelectric catalyst is designed and tested for the generation of hydrogen peroxide (H2O2). It is based on Nb‐doped tetragonal BaTiO3 (BaTiO3:Nb) and is sensitized by carbon quantum dots (CDs). The photosensitizer injects electrons into the conduction band of the semiconductor, while the piezoelectric polarization directed electrons to the semiconductor surface, allowing for a high‐rate generation of H2O2. The piezoelectric polarization field restricts the recombination of photoinduced electron–hole pairs. A production rate of 1360 µmol gcatalyst−1 h−1 of H2O2 is achieved under visible light and ultrasound co‐irradiation. Individual piezo‐ and photocatalysis yielded lower production rates. Furthermore, the CDs enhance the piezocatalytic activity of the BaTiO3:Nb. It is noted that moderating the piezoelectricity of BaTiO3:Nb via microstructure modulation influences the piezophotocatalytic activity. This work shows a new methodology for synthesizing H2O2 by using visible light and mechanical energy.

Piezoelectricity of two-dimensional (2D) materials with a noncentrosymmetric atomic structure is important to be studied and can be widely applied in many areas. Ti3C2Tx, as a kind of MXene, is able to be modified with functional groups and loses its central symmetry. Here, the mechanical-piezoelectric coupling equations of the Ti3C2Tx MXene with narrow band gaps are proposed to reveal the origin of piezoelectricity in monolayer Ti3C2Tx MXene. The multilayer 2D structure presents the extraordinary piezoelectric properties of the Ti3C2Tx MXene. Then, the modulation of the Schottky barrier by continuous piezoelectric potential distribution in Ti3C2Tx MXene and the nonuniform distribution of piezoelectric potential between unique polyatomic layer structures are described through the establishment of theoretical model, which explains the origin of the high conversion efficiency. Finally, the piezoelectric effect in multilayer Ti3C2Tx MXene as the circular piezoelectric resonator is analyzed. It is believed that the establishment of the atomic piezoelectric polarization model provides a solid foundation for understanding the piezoelectric mechanism in the Ti3C2Tx MXene and the preparation of piezoelectric devices such as a piezoelectric tactile sensor system, piezoelectric nanogenerator, and nanopiezoelectric resonator. [ABSTRACT FROM AUTHOR]

This study investigates the impact of In- and S-vacancy concentrations on the photocatalytic activity of non-centrosymmetric zinc indium sulfide (ZIS) nanosheets for the hydrogen evolution reaction (HER). A positive correlation between the concentrations of dual In and S vacancies and the photocatalytic HER rate over ZIS nanosheets is observed. The piezoelectric polarization, stimulated by low-frequency vortex vibration to ensure the well-dispersion of ZIS nanosheets in solution, plays a crucial role in enhancing photocatalytic HER over the dual-vacancy engineered ZIS nanosheets. The piezoelectric characteristic of the defective ZIS nanosheets is confirmed through the piezopotential response measured using piezoelectric force microscopy. Piezophotocatalytic H 2 evolution over the ZIS nanosheets is boosted under accelerated vortex vibrations. The research explores how vacancies alter ZIS's dipole moment and piezoelectric properties, thereby increasing electric potential gradient and improving charge-separation efficiency, through multi-scale simulations, including Density Functional Theory and Finite Element Analysis, and a machine-learning interatomic potential for defect identification. Increased In and S vacancies lead to higher electric potential gradients in ZIS along [100] and [010] directions, attributing to dipole moment and the piezoelectric effect. This research provides a comprehensive exploration of vacancy engineering in ZIS nanosheets, leveraging the piezopotential and dipole field to enhance photocatalytic performances., (© 2024 Wiley‐VCH GmbH.)

The effects of spontaneous and piezoelectric polarizations on the intersubband absorption in the GaN/ZnGeN2 quantum well are studied. Schrödinger and Poisson equations are solved self-consistently. The first order linear and third order nonlinear absorption coefficients of the intersubband transitions originating from ground and first excited states are calculated. We have presented the results relative to polarization, doping level and well length. The polarization causes the absorption peak to be reduced and shifted to higher energies, and the nonlinear absorption to become weaker, but this effect is slightly reversed with doping. The effect of polarization or doping increases with well length, but they are observed after 26 Å. [ABSTRACT FROM AUTHOR]

The key factor for efficient photoelectrochemical (PEC) water splitting is to design a semiconductor as photoanode with high carrier separation. Piezoelectric polarization is a considerable method to improve the carriers separation efficiency via providing a powerful built-in electric field. Herein, we synthesized WO 3 /CdS type II heterojunction and firstly explored the influence of CdS phase transition from sphalerite β-CdS to wurtzite α-CdS on piezoelectric polarization for WO 3 /CdS. Benefited from the asymmetric structure of α-CdS, fluctuation swings can be seen in the LSV curves of WO 3 /α-CdS due to piezoelectric polarization under ultrasound. The photocurrent density of WO 3 /α-CdS are enhanced with the increase of ultrasound frequency and the maximum of 2.13 mA/cm2 at 1.23 V vs. RHE, which is 1.61 times before ultrasound. The outstanding PEC performances of WO 3 /α-CdS under ultrasonic conditions are contributed to carrier separation driven by enhancing internal electric field between heterojunction, the built-in electric field inside the α-CdS and ballast carriers participating in water splitting reaction. This work provides a promising strategy for improving carrier separation efficiency in photoelectrodes via piezoelectric polarization. • WO 3 /α-CdS and WO 3 /β-CdS were used as photoanode in PEC water splitting. • CdS as the primary light absorber improves the light utilization efficiency. • WO 3 /α-CdS heterojunction is built to further carrier separation and transfer driven by internal electric field. • Piezoelectric polarization of α-CdS provides another built-in electric field which reduces the recombination of carriers. • The ballast carriers generated by piezoelectric polarization participates in the water splitting reaction. [ABSTRACT FROM AUTHOR]

This paper presents a systematic approach to transduction optimization of resonant piezo-based MEMS devices. The method is based on inverse design approach using direct piezoelectric effect and exploits mechanical action of desired mode to calculate the polarization map of the piezoelectric ceramics. Optimal transduction is achieved by matching the excited electric field distribution to the inversely retrieved polarization map using the electrode segmentation and topology optimization technique. The proposed method was applied to improve the design of existing state-of-the-art piezoelectric MEMS mirrors. The optimized devices feature 70% increase in the optical scan angle (θopt) as well as 47 % reduction in power consumption compared to original design. At the same optical scan angle, the optimized devices required 2.28-fold less driving voltage amplitude. [2020-0342] [ABSTRACT FROM AUTHOR]

The dependence of electromechanical behavior on strain in ferroelectric materials can be leveraged as parameter to tune ferroelectric properties such as the Curie temperature. For van der Waals materials, a unique opportunity arises because of wrinkling, bubbling, and Moiré phenomena accessible due to structural properties inherent to the van der Waals gap. Here, we use piezoresponse force microscopy and unsupervised machine learning methods to gain insight into the ferroelectric properties of layered CuInP2S6 where local areas are strained in-plane due to a partial delamination, resulting in a topographic bubble feature. We observe significant differences between strained and unstrained areas in piezoresponse images as well as voltage spectroscopy, during which strained areas show a sigmoid-shaped response usually associated with the response measured around the Curie temperature, indicating a lowering of the Curie temperature under tensile strain. These results suggest that strain engineering might be used to further increase the functionality of CuInP2S6 through locally modifying ferroelectric properties on the micro- and nanoscale. [ABSTRACT FROM AUTHOR]

Rare earth (RE = La, Er, and YbFeO3) ferrites are prepared from their nitrate precursors using the solution combustion method. Structural analysis using powder X-ray diffraction (XRD) technique indicates that the synthesized La-, Er-, and Yb–FeO3 perovskite nanoparticles have pure phase orthorhombic super unit cells. The XRD patterns of Er–FeO3 and Yb–FeO3 are found to be indexed in Pbnm (62) space group with cell dimensions in the range of ao = 5.2611–5.2784 Å, bo = 5.5729–5.5898 Å, and co = 7.596–7.6002 Å, while the space group of Pnma (62) with ao = 5.5688 Å, bo = 7.8523 Å, and co = 5.5542 Å are obtained for LaFeO3. Surface morphological studies show aggregated spherical-shaped nanoparticles having an orthorhombic crystal structure with an average particle size of ~ 50 nm. Magnetic properties of all the three RE ferrite synthesized in this work exhibit antiferromagnetic behavior. The study of dielectric properties of all the three RE ferrites shows dispersive behavior at low frequencies with low loss. Temperature-dependent dielectric studies confirm that the antiferromagnetic-paramagnetic transition temperature appears at 445 K. A larger P-E loop with a squareness ratio of 1.583 for ErFeO3 orthoferrites suggests that it is more advantageous than LaFeO3 and YbFeO3 for making modern electronic devices. [ABSTRACT FROM AUTHOR]

Rare earth (RE = La, Er, and YbFeO3) ferrites are prepared from their nitrate precursors using the solution combustion method. Structural analysis using powder X-ray diffraction (XRD) technique indicates that the synthesized La-, Er-, and Yb–FeO3 perovskite nanoparticles have pure phase orthorhombic super unit cells. The XRD patterns of Er–FeO3 and Yb–FeO3 are found to be indexed in Pbnm (62) space group with cell dimensions in the range of ao = 5.2611–5.2784 Å, bo = 5.5729–5.5898 Å, and co = 7.596–7.6002 Å, while the space group of Pnma (62) with ao = 5.5688 Å, bo = 7.8523 Å, and co = 5.5542 Å are obtained for LaFeO3. Surface morphological studies show aggregated spherical-shaped nanoparticles having an orthorhombic crystal structure with an average particle size of ~ 50 nm. Magnetic properties of all the three RE ferrite synthesized in this work exhibit antiferromagnetic behavior. The study of dielectric properties of all the three RE ferrites shows dispersive behavior at low frequencies with low loss. Temperature-dependent dielectric studies confirm that the antiferromagnetic-paramagnetic transition temperature appears at 445 K. A larger P-E loop with a squareness ratio of 1.583 for ErFeO3 orthoferrites suggests that it is more advantageous than LaFeO3 and YbFeO3 for making modern electronic devices. [ABSTRACT FROM AUTHOR]

An electromechanically coupled modeling framework for the simulation of electric current flow in ZnO varistors is developed. The model is based on an equivalent circuit representation of the varistor microstructure with grain boundaries represented by nonlinear resistor branches of the circuit. This approach extends on previous circuit models by including the effect of mechanical stress on grain boundary conductivity. In this article, we consider, in particular, the effect of residual thermal stress in polycrystalline structures on electrical conductivity. The distribution of this stress throughout the material is computed by finite element method (FEM) simulations. Then, each grain boundary conductivity is determined by applying a self-consistent model for the trapped interface charge induced by piezoelectric polarization. Finally, the electric current flow patterns and the bulk conductivity of the material are computed using the nonlinear circuit model. The simulated I–V characteristics reveal a significant sensitivity of the electrical conductivity to internal thermal stress within the material. Furthermore, for realistic ZnO microstructures, the simulations demonstrate the effect of current concentration along thin conducting paths depending on the mechanical stress condition of the material. [ABSTRACT FROM AUTHOR]

Piezoelectric polarization can provide a strong driving force to accelerate the separation and migration of photo-generated carriers, enabling more electrons and holes to migrate to the surface of the Bi 3 TiNbO 9 nanosheets. Meanwhile, the piezo-potential will induce the band bending, which can adjust the band structure to enhance the redox abilities of catalyst. [Display omitted] • Bi 3 TiNbO 9 nanosheets were synthesized by an one-step hydrothermal method. • Piezocatalytic and piezo-photocatalytic performance of Bi 3 TiNbO 9 were explored. • Piezoelectric polarization accelerates the separation and migration of photocharges. • Bi 3 TiNbO 9 shows universal piezo-photocatalytic degradation performance and excellent durability. Photocatalysis is considered as a green and efficient technology for dealing with water pollution problems, but there exists serious carrier recombination in photocatalysis. Introducing a piezoelectric field to reduce carrier recombination and accelerate carrier separation and migration is a recognized as an effective approach, while it remains testing for exploitation for high-performance catalysts with light and stress dual response as well as the coupling catalytic mechanism. In this work, we report a novel layered perovskite structure piezo-photocatalyst Bi 3 TiNbO 9 and conducted an analysis of potential piezo-photocatalytic mechanisms. The piezoelectric force microscopy (PFM) and COMSOL finite element analysis prove that the Bi 3 TiNbO 9 is a piezoelectric with strong piezoelectricity. In the degradation of tetracycline hydrochloride, Bi 3 TiNbO 9 exhibits significantly better piezo-photocatalysis performance compared to piezocatalysis and photocatalysis. It is owing to that the ultrasound results in piezoelectric polarization accompanied by the generation of piezo-potential, which can induce piezocatalysis and facilitate the separation and transfer of photo-generated carriers. Electron paramagnetic resonance (EPR) technique and electrochemical tests are carried out under different excitation sources to identify the dominant active species involved in the reaction and to disclose the origin for the high performance of piezo-photocatalysis from the perspective of carriers. This study adds a new member to the family of piezo-photocatalytic material system, and provides further understanding on the synergistic piezo-photocatalysis mechanism. [ABSTRACT FROM AUTHOR]

The light and stress dual-responsive Bi 2 O 2 (OH)NO 3 /BiOI heterojunction is developed, and the synergy of interfacial electric field and piezoelectric polarization enables it exceptional piezo-photocatalytic performance. [Display omitted] • Bi 2 O 2 (OH)NO 3 /BiOI type-II heterostructure is created through in-situ deposition. • Bi 2 O 2 (OH)NO 3 /BiOI has 1.6 times higher surface potential than BON, suggesting a stronger electric field. • Built-in electric field and piezoelectric polarization greatly enhances charge separation. • It shows exceptional piezo-photocatalytic TH degradation of 80 % within just 10 min. Effective removal of recalcitrant pollutants is crucial for environmental protection. Tetracycline hydrochloride, as a representative recalcitrant organic pollutant, poses a potential threat to environmental integrity when present in aquatic ecosystems. Coupling piezoelectric polarization, capable of considerably promoting the photocharge separation, acts as a very prevalent and attractive strategy to improve the photocatalytic activity. In this study, an efficient piezo-photocatalytic system was developed in Bi 2 O 2 (OH)NO 3 /BiOI heterojunction by collaborating with interfacial electric field and vibration-induced piezoelectric polarization. The construction of type II heterojunction allows an interfacial electric field to propel the photogenerated electrons from BiOI to Bi 2 O 2 (OH)(NO 3) under visible light irradiation. The introduction of vibration-induced piezoelectric polarization field strengthens the interfacial electric field, which further promote the separation and migration of photogenerated charges. Profiting from the above advantages, Bi 2 O 2 (OH)(NO 3)/BiOI heterojunction exhibited a remarkable piezo-photocatalytic performance, achieving an over 80% degradation efficiency of tetracycline hydrochloride within 10 min, which far surpasses that under individual photocatalysis or ultrasound-induced piezocatalysis and also exceeds most of the previously reported piezo-photocatalysts. The combination of electron paramagnetic resonance, piezoresponse force microscopy, COMSOL simulation, and photoelectrochemical tests are conducted to probe the synergistically-catalytic mechanism. This work not only elucidates the comprehensive impact of interfacial electric field and piezoelectric polarization on charge separation, but also highlights the tremendous potential of piezo-photocatalysis for environmental remediation. [ABSTRACT FROM AUTHOR]

In deep-ultraviolet (DUV) light-emitting diodes (LEDs), it is difficult to obtain both efficient carrier confinement and high light extraction, which are quite sensitive to optical polarization and other physical parameters. In this paper, characteristics of DUV LEDs with various n-AlGaN layers and quantum barriers (QBs), and various widths of quantum wells (QWs) are investigated. Specifically, the capability of carrier confinement and properties of optical polarization are analyzed in detail. The simulation results show that LED structure with Al0.64Ga0.36N QBs, n-Al0.7Ga0.3N layer, and 4-nm-thick QWs, which has a peak emission wavelength of 284.5 nm at 60 mA, exhibits high internal quantum efficiency of 25% and high degree of optical polarization of 0.874. [ABSTRACT FROM AUTHOR]

• Flexible black BaTiO 3 nanofiber films were prepared by sol–gel electrospinning and in-situ reduction. • Ultrasonic Cavitation Enhanced Photocatalytic CO 2 Reduction to syngas. • By changing the cavitation conditions, the CO and H 2 ratio can be adjusted precisely. Photocatalytic CO 2 reduction is an attractive strategy to realize carbon–neutral economy but is challenging by its low efficiency and uncontrollable selectivity. Here, we report a new flexible black BaTiO 3 nanofiber (B-BTO NF) and prove its unique function of ultrasonic cavitation enhanced photocatalytic CO 2 reduction into controllable syngas. The B-BTO NFs with a large deformation ability and a high mechanical strength contain unsaturated Ti3+ coordination and vacancy defects. Under ultrasound, the NF film gathers abundant cavitation bubbles, and the continual explosions of these bubbles bring periodic piezoelectric polarization changes and release net charges on B-BTO NFs, thus triggering photocatalytic CO 2 reduction into syngas. Moreover, the product selectivity can be controlled by facilely adjusting the ultrasonic frequency and power. As a result, the evolution rate of target syngas (CO/H 2 ≈ 1:1.3) reaches as high as 12525 μmol/g/h. The proposed flexible B-BTO NF induced ultrasonic cavitation-enhancement strategy provides new insights for designing photocatalysts. [ABSTRACT FROM AUTHOR]

Using the effective mass model for an electron and the dielectric continuum model, analytical solutions of the self-consistent Schrodinger-Poisson system of equations are obtained. Quantum mechanical theory of electronic stationary states, the oscillator strengths of quantum transitions and a method of potential profile calculation is developed for the experimentally constructed three-well resonance-tunneling structure -- a separate cascade of quantum cascade detector. For the proposed method, a comparison with the results of other methods and with the results of the experiment was carried out. A good agreement between the calculated value of the detected energy and its experimental value has been obtained, the difference being no more than 2.5%. [ABSTRACT FROM AUTHOR]

This paper derives theoretical solutions for three radially layered piezoceramic/epoxy cylindrical composite transducers, which are composed of a solid epoxy disk, two axially polarized piezoceramic rings, and two epoxy rings. Two piezoceramic rings are the functional components, which can actuate and adjust the composite’s performance. According to different functions, three typical transducers are developed. The first one involves both of the two piezoceramic rings acting as actuating elements with parallel connections electrically. The other two involve only one piezoceramic ring as an actuating element, while the other ring that is connected to a resistor acts as a sensing element to adjust the electromechanical characteristics. Based on the plane stress assumption, theoretical solutions of these three transducers in radial vibration are derived, and performance differences of their electromechanical characteristics are analyzed and discussed. Furthermore, the solutions are validated by comparing with the ANSYS simulation results and the experimental data. The simulated and the measured first resonance and antiresonance frequencies are in a good agreement with the theoretical results, which validates the accuracy of the directed solution. This paper contributes to a comprehensive understanding of the proposed cylindrical composite’s electromechanical performance, which is helpful for further application in underwater sound and ultrasonic fields. [ABSTRACT FROM AUTHOR]

A versatile mass-sensing platform based on the nonlinear dynamical response of a microcantilever embedded in a self-excitation feedback loop is proposed. It is experimentally shown that the delay imposed in the feedback loop by an adjustable phase-shifter can be used to finely tune this system to work in three different modalities, according to the desired mass sensing application: 1) as a continuous mass sensor, where the oscillation frequency smoothly responds to changes in the mass added to the resonator; 2) as a threshold sensor, where a sudden change in the oscillation frequency is triggered by an arbitrarily small change of mass added to the cantilever; and 3) as a stable microresonator, whose oscillation frequency is almost not affected by environmental conditions, such as changes in added mass, or in density/viscosity of the surrounding fluid. This variety of dynamical responses was registered for a wide range of added masses, in the form of beads individually attached to the cantilever. A complete analytical model to explain the observed experimental results is derived and shows a strong agreement with the measured data. The high resolution and signal-to-noise ratio, as well as the threshold and stable sensing modalities obtained with this closed-loop technique, are not available in the current open-loop microcantilever-based mass sensors. [ABSTRACT FROM AUTHOR]

Within the dielectric continuum model and the model of effective masses for the electron, self-consistent solutions to the Schrodinger-Poisson system of equations taking into account the contribution of piezoelectric and spontaneous polarizations were found. The theory of stationary electronic states, taking into account the internal fields caused by piezoelectric and spontaneous polarizations occurring in the nanostructure was developed for the three-barrier wurtzite anisotropic resonance-tunneling structure with binary and ternary components. For nanostructure, which functioned as a cascade of experimentally realized quantum cascade detector, the calculation of the potential profile, stationary electron energy spectrum and oscillator strengths of quantum transitions was carried out. The geometric configurations of the nanostructure, for which the intensity of the detector quantum transitions between the working energetic states is the largest, were established. [ABSTRACT FROM AUTHOR]

Piezoelectric polarization and interfacial electric field are integrated in Bi 2 O 2 (OH)NO 3 -Bi 2 MoO 6 heterojunction photocatalysts synthesized via in situ transformation method, which synergistically promotes the piezo-photocatalytic activity. [Display omitted] • Bi 2 O 2 (OH)NO 3 -Bi 2 MoO 6 heterojunction with strong interfacial electric field is synthesized. • Introduction of ultrasound vibration provides piezoelectric polarization and effective piezocatalysis. • Interfacial electric field and piezoelectric polarization cooperatively promote the separation and transfer of photogenerated charges. • Bi 2 O 2 (OH)NO 3 -Bi 2 MoO 6 displayed efficient piezo-photocatalytic degradation of TC. Photocatalysis is a promising approach for purifying water pollutants resources, but is greatly restricted by rapid photogenerated charges recombination. Herein, Bi 2 O 2 (OH)NO 3 -Bi 2 MoO 6 heterojunction photocatalysts with strong interfacial electric field are synthesized via in situ transformation method with using Bi 2 O 2 (OH)NO 3 as a self-sacrificial template. The intimate interface interaction renders a large interfacial potential, which allows efficient charge separation within the heterojunction. Thus, the photocatalytic activity was well optimized compared with the pristine catalyst and composite counterpart prepared by in situ growth route. Then, the piezoelectric polarization induced by ultrasonic vibration is introduced in the photocatalytic system, which yields a piezocatalytic activity and enhancement on the separation and transfer of photogenerated charge carriers. Benefiting from the piezoelectric polarization and interfacial electric field, the in situ transformed Bi 2 O 2 (OH)NO 3 -Bi 2 MoO 6 heterojunction exhibits a prominent piezo-photocatalytic performance for degradation of tetracycline, much higher than that under sole light or ultrasound irradiation source as well as the individual catalyst. This work reveals the potential of the collaboration of piezoelectric polarization and interfacial electric field in photocatalysis. [ABSTRACT FROM AUTHOR]

The broad application prospects of two-dimensional (2D) materials have stimulated considerable interest in exploring their piezoelectric properties. Ti 3 C 2 Tx MXene has been predicted to possess highly directional piezoelectric properties, owing to its non-centrosymmetric lattice structure. This study presents the experimental piezo-response of oxidized-MXene, which demonstrates that different atomic structure of oxidized-MXene induces unexpected oscillating piezoelectric performance. The presence of surface-modified groups on the Ti 3 C 2 Tx-O MXene breaks the inversion symmetry of the lattice structure, thereby exhibiting strongly enhanced piezoelectric behavior. Specifically, the armchair direction of the Ti 3 C 2 Tx-O MXene manifests an inherent current output of 1.15 ± 0.20 nA under the tensile strain of 1.30%, yielding a power density of ∼31.04 mW/m2 and a conversion efficiency of ∼17.4%. These values excess those of previously reported 2D materials. Theoretical calculations have provided insights into the underlying mechanisms of piezoelectric polarizations in the multi-atomic structure of various oxidized-MXenes. The discovery of piezo-oxidized-MXene offers a promising avenue for exploring the potential of MXene in the development of nanodevices and stretchable electronics. [Display omitted] • The study shows that different atomic structure of oxidized-MXene induces different oscillating piezoelectric performance. • The surface-modified groups break the inversion symmetry of the lattice structure, resulting in enhanced piezoelectricity. • The Ti 3 C 2 Tx-O MXene sheet exhibits the maximum piezoelectric power of 3.73 × 10−13 W and conversion efficiency of 17.4%. [ABSTRACT FROM AUTHOR]

Controlling carrier separation by regulating polarization intensity is of great significance for built-in electric field assisted photoelectrochemical (PEC) water splitting. Here, we synthesize BiFeO 3 /PVDF composite photoelectrodes by loading a certain amount of PVDF on BiFeO 3 films. The strong piezoelectric effect of PVDF can improve their piezoelectric built-in electric field to drive carrier separation, and the composite photoelectrode after alkali etching also has an improvement in hydrophily, thus together improving the piezoelectric PEC water splitting. The maximum photocurrent density of BiFeO 3 /PVDF composite photoelectrodes can be up to 2.03 mA/cm2 at 1.23 V vs RHE, which is significantly enhanced over the photocurrent of bare BiFeO 3. In addition, the photocurrent density of BiFeO 3 /PVDF photoelectrode after alkali etching reaches 2.51 mA/cm2 at 1.23 V vs RHE. The influence of polarization intensity and hydrophilicity on PEC water splitting performance is studied systematically through BiFeO 3 /PVDF composite systems. This work provides a strategy for designing high activity photoanodes for PEC water splitting in organic/inorganic composites. [Display omitted] [ABSTRACT FROM AUTHOR]

Polyvinylidene difluoride (PVDF) polymers are widely used in triboelectric nanogenerators (TENGs) due to their excellent dielectric and piezoelectric properties. To design a high-performance TENG, it is essential to investigate the individual contributions of these properties on contact electrification (CE). In this work, a range of PVDF, co- and terpolymers are used to assess the distinct contributions of dielectric and piezoelectric properties on the TENG's output. As elucidated by a modified overlapped electron cloud model (OEC) supported with Kelvin Probe Force Microscopy (KPFM) measurements, the high dielectric constant in terpolymers hinders electron backflow after CE, while piezoelectric polarization in β -phase PVDF shifts its electron energy levels before CE. Notably, in PVDF polymers, the dielectric and piezoelectric enhancements to TENGs come at the expense of one another. To verify this phenomenon, the terpolymers are cooled to alter their phases from relaxor to regular ferroelectrics, diminishing their dielectric constants while increasing their piezoelectric polarizations. Initially, the output is high (10.2 W/m2) at room temperature during the relaxor ferroelectric phase which is due to the high dielectric constant. Upon cooling, the output decreased to its lowest during the phase transition (4.3 W/m2 at 0 °C), as a result of the tradeoff between dielectric and piezoelectric enhancement. When the temperature was further tuned down to − 40 °C, the output reaches the maximum of 16 W/m2, which is attributed mainly to the ferroelectric phase. For the first time, the phase transition is observed and evidenced by electric field-induced dielectric and ferroelectric measurements, proving the piezoelectric polarization of PVDF terpolymers. These findings therefore provide guidelines on material selection and pave the way for potential low-temperature TENG applications. [Display omitted] • Dielectric constant enhances TENG via improved surface charge retention. • Piezoelectric polarization enhances TENG via shifting of electron energy levels. • Ferroelectric phase in PVDF terpolymers is induced via low temperature. • This is proven by field-induced dielectric measurements for the first time. • Piezoelectric enhancement at low temperatures generated a maximum of 16 W/m2. [ABSTRACT FROM AUTHOR]