Intrinsic Piezoelectricity Research Articles

A perspective on mechanoluminescence and multipiezo in ferroelectric materials

The discovery of innovative mechanoluminescence materials of SrAl2O4 and ZnS, which emit repeatable light [repeatable mechanoluminescence (ML), hereafter simply ML] even by soft touch, has trigged intense research interest in material/device/system development for applications across various fields. This perspective presents an overview of the crystal structures, mechanisms, and ML behaviors of most promising systems, namely, SrAl2O4-, ZnS-, LiNbO3-, and Sr3Sn2O7-based ferroelectric materials. These multipiezo materials, which simultaneously exhibit intrinsic piezoluminescence (true elastic deformation induced ML and no friction effect) and piezoelectricity, show distinct and valuable characteristics by integrating mechanical force, electric field, and light for stress sensing and other applications. Recent studies indicated the critical role of crystal structure, doping, and piezoelectric properties in achieving robust and reliable ML performance. These findings suggest that ML materials hold substantial promise for applications in stress/force sensing, structural health monitoring, mechanically activated lighting, and advanced imaging techniques. Further investigation and advancement of multipiezo materials could yield breakthroughs, further augmenting their usefulness across various industries and scientific domains. Exploring ferroelectric ML materials offer new prospects for developing advanced materials with unique electro-mechano-optical properties.

Textured Asymmetric Membrane Electrode Assemblies of Piezoelectric Phosphorene and Ti3C2Tx MXene Heterostructures for Enhanced Electrochemical Stability and Kinetics in LIBs

HighlightsAn asymmetric membrane electrode based on phosphorene/MXene heterostructure-textured nanopiezocomposite was fabricated via a polar urea-assisted self-assembly strategy and additive manufacturing of the heterostructure beyond the skin effect.The merits of this novel asymmetric heterostructure-textured electrode and its intrinsic piezoelectricity were detailedly discussed.The stepwise lithiation process of phosphorene was revealed, and the enhanced electrochemical properties of this phosphorene-based nanopiezocomposite textured electrode were verified by the improved cycling stability and kinetics.

Observation of piezoelectricity in a lead-free Cs2AgBiBr6 perovskite: a new entrant in the energy harvesting arena.

Halide perovskite materials have recently been recognised as powerful ferroelectric and piezoelectric materials with applications in the energy harvesting arena, but their experimental proof is very limited. We achieved strong intrinsic piezoelectricity in the lead-free inorganic double perovskite Cs2AgBiBr6 at room temperature and utilized it for mechanical energy harvesting, with a piezoelectric co-efficient (d33) of 12.7 pC N-1. Hysteresis loop and structural analyses offered further validation for the substantial ferroelectric features of the as-synthesised double perovskite. Density functional theory (DFT) calculations revealed the presence of anharmonic phonon soft modes in tetragonal Cs2AgBiBr6 due to dynamic instability, which resulted in piezoelectricity. Under an optimal pressure of ≈25 kPa, a Cs2AgBiBr6 thin film-based piezoelectric nanogenerator device delivered instantaneous output values of ≈45 V and ≈200 nA. The strain-sensitive responses of the device were also exemplified to identify specific body motions from the detected instantaneous output values. The energy obtained from the device is shown to be effective for capacitor charging and commercial light-emitting diode (LED) lighting. Our study provides significant insights into the dielectric behaviour of materials as well as piezo- and ferroelectric behaviours, which are crucial for the development of modern electronic and energy harvesting devices.

The local atomic distribution in tetragonal PZT

Expanding on the comprehensive research conducted by previous scholars. Herein, to elucidate the intrinsic piezoelectricity of tetragonal Pb(Zr1-xTix)O3 (PZT), we focus on the local atomic distribution which was neglected for...

Novel Sandwich-Structured Flexible Composite Films with Enhanced Piezoelectric Performance.

Piezoelectric poly(vinylidene fluoride) (PVDF) and its copolymers have been widely investigated for applications in wearable electric devices and sensing systems, owing to their intrinsic piezoelectricity and superior flexibility. However, their weak piezoelectricity poses major challenges for practical applications. To overcome these challenges, we propose a two-step synthesis approach to fabricate sandwich-structured piezoelectric films (BaTiO3@PDA/PVDF/BaTiO3@PDA) with significantly enhanced ferroelectric and piezoelectric properties. As compared to pristine PVDF films or conventional 0-3 composite films, a maximum polarization (Pmax) of 11.24 μC/cm2, a remanent polarization (Pr) of 5.83 μC/cm2, and an enhanced piezoelectric coefficient (d33 ∼ 14.6 pC/N) were achieved. Simulation and experimental results have demonstrated that the sandwich structure enhances the ability of composite films to withstand higher poling electric fields in comparison with 0-3 composites. The sandwich-structured piezoelectric films are further integrated into a wireless sensor system with a high force sensitivity of 288 mV/N, demonstrating great potential for movement monitoring applications. This facile approach shows great promise for the large-scale production of composite films with remarkable flexibility, ferroelectricity, and piezoelectricity for wearable sensing devices.

Chitosan based aerogel fibers for piezoelectric and moisture electric energy harvesting

Taking advantages of renewable resourced materials in the preparation of multifunctional aerogel fibers which integrate thermal insulation, piezoelectric and moisture electric generation could be a promising way of relieving pressure on both energy loss and generation. A series of chitosan-konjac glucomannan (CS-KGM) aerogel fibers was obtained by means of wet-spinning method followed by freeze-drying. The CS-KGM aerogel fibers with submicron porous morphology exhibit excellent thermal insulation performance. Single layer of CS-KGM aerogel fiber with only a thickness of 0.6 mm shows a thermal insulation temperature difference of 23 °C. A stable piezoelectric output voltage of 0.35 V can be generated from a single CS-KGM aerogel fiber during a 500 press-release cycle attributing to the intrinsic piezoelectricity of CS and the porous structure. Single aerogel fibers were coated with multi-walled carbon nanotubes as a way to prepare conductive aerogels. Meanwhile, the moisture electric output voltage can be as high as 160 mV and last for >8 h at 60% relative humidity for CS-KGM single aerogel fiber assisted by a thin layer of carbon nanotube coating. Overall, CS-KGM aerogel fibers prepared in this work has good compatibility and potential applications in thermal management and energy harvesting from low density resource, which provides a new strategy for the preparation of sustainable and multifunctional wearable materials.

Piezoelectric Ba0.85 Sr0.15 TiO3 Nanosonosensitizer with Nitric Oxide Delivery for Boosting Cancer Therapy.

The efficacy of sonodynamic therapy (SDT) mainly relies on the sonosensitizers, which generate reactive oxygen species (ROS) upon ultrasound (US) stimulation. However, the limited availability of high-efficiency sonosensitizers hampers the therapeutic effectiveness of SDT as a standalone modality. In this work, a robust sonodynamic and gas cancer therapeutic platform is constructed based on strontium (Sr) doped barium titanate (BST) piezoelectric nanoparticles functionalized with L-arginine (BST@LA). The doping of Sr into A site of the ABO3 piezoelectric nanocrystals not only introduces oxygen vacancies into the nanoparticles and enhance the intrinsic piezoelectricity, but also narrows the semiconductor band gap and enhances charge carrier migration, all of which facilitate the sonodynamic production of superoxide anion (•O2 - ) and hydroxyl radical (•OH). In addition, the generated ROS promotes the decomposition of the surface-tethered LA, enabling the controlled release of nitric oxide (NO) gas at the tumor site, thereby achieving a combination therapeutic effect. In vivo experiments exhibit remarkable tumor suppression rate (89.5%) in 4T1 tumor mice model, demonstrating the effectiveness of this strategy. The ion doping and oxygen vacancy engineering to improve sonosensitizers, along with the synergistic combination of sonodynamic and gas therapy, provides promising avenues for improving cancer therapy.

Low-Temperature Centimeter-Scale Growth of Layered 2D SnS for Piezoelectric Kirigami Devices.

Tin monosulfide (SnS) is a promising piezoelectric material with an intrinsically layered structure, making it attractive for self-powered wearable and stretchable devices. However, for practical application purposes, it is essential to improve the output and manufacturing compatibility of SnS-based piezoelectric devices by exploring their large-area synthesis principle. In this study, we report the chemical vapor deposition (CVD) growth of centimeter-scale two-dimensional (2D) SnS layers at temperatures as low as 200 °C, allowing compatibility with processing a range of polymeric substrates. The intrinsic piezoelectricity of 2D SnS layers directly grown on polyamides (PIs) was confirmed by piezoelectric force microscopy (PFM) phase maps and force-current corroborative measurements. Furthermore, the structural robustness of the centimeter-scale 2D SnS layers/PIs allowed for engraving complicated kirigami patterns on them. The kirigami-patterned 2D SnS layer devices exhibited intriguing strain-tolerant piezoelectricity, which was employed in detecting human body motions and generating photocurrents irrespective of strain rate variations. These results establish the great promise of 2D SnS layers for practically relevant large-scale device technologies with coupled electrical and mechanical properties.

Precisely Orientating Atomic Array in One-Dimension Tellurium Microneedles Enhances Intrinsic Piezoelectricity for an Efficient Piezo-Catalytic Sterilization.

Comprehensively understanding the interdependency between the orientated atomic array and intrinsic piezoelectricity in one-dimension (1D) tellurium (Te) crystals will greatly benefit their practical piezo-catalytic applications. Herein, we successfully synthesized the various 1D Te microneedles by precisely orientating the atomic growth orientation by tuning (100)/(110) planes ratios (Te-0.6, Te-0.3, Te-0.4) to reveal the secrets of piezoelectricity. Explicitly, the theoretical simulations and experimental results have solidly validated that the Te-0.6 microneedle grown along the [110] orientation possesses a stronger asymmetric distribution of Te atoms array causing the enhanced dipole moment and in-plane polarization, which boosts a higher transfer and separation efficiency of the electron and hole pairs and a higher piezoelectric potential under the same stress. Additionally, the orientated atomic array along the [110] has p antibonding states with a higher energy level, resulting in a higher CB potential and a broadened band gap. Meanwhile, it also has a much lower barrier toward the valid adsorption of H2O and O2 molecules over other orientations, effectively conducive to the production of reactive oxygen species (ROS) for the efficient piezo-catalytic sterilization. Therefore, this study not only broadens the fundamental perspectives in understanding the intrinsic mechanism of piezoelectricity in 1D Te crystals but also provides a candidate 1D Te microneedle for practical piezo-catalytic applications.

Ferroelectric Polarization‐Enhanced Performance of Flexible CuInP2S6 Piezoelectric Nanogenerator for Biomechanical Energy Harvesting and Voice Recognition Applications

Abstract2D piezoelectric materials have strong intrinsic piezoelectricity and superior flexibility, which are endowed with huge potential to develop piezoelectric nanogenerators (PENGs). However, there are few attempts to investigate the energy harvesting of 2D ferroelectric materials. Herein, an enhanced output performance is reported by ferroelectric polarization in a PENG with exfoliated 2D ferroelectric CuInP2S6 (CIPS). Specifically, the polarized CIPS‐based PENG produces a short‐circuit current of 760 pA at 0.85% tensile strain, which is 3.8 times higher than that of unpolarized CIPS‐based PENG. Systematical PFM and Raman analysis reveal that the ferroelectric polarization remarkably reinforces the effective piezoelectric constant of CIPS nanoflakes and boosts the in‐plane migration and out‐of‐plane hopping of copper ions, which is the main reason for the enhancement of output performance. Furthermore, the CIPS‐based PENG can not only be utilized to harvest biomechanical energy such as wrist joints movement, but also exhibits a potential for a voice recognition system integrated with deep learning technology. The classification accuracy of a series of letter sounds is as high as 96%. This study commendably broadens the application scope of 2D materials in micro‐nano energy and intelligent sensors, which will have profound implications for exploring wearable nanoelectronic devices.

Determination of the key role to affect the piezocatalytic activity of graphitic carbon nitride for tetracycline hydrochloride degradation in water

Graphitic carbon nitride (g-C3N4) has been proved to possess intrinsic piezoelectricity and its two-dimensional (2D) nanosheets present piezocatalytic activity to produce hydrogen from water splitting and eliminate organic pollutants in wastewater. Specific surface area and piezoelectric polarization are of great significance to achieve high piezocatalytic activity, but it is difficult to simultaneously improve both of them. Herein, to reveal the dominant role in the piezocatalysis of g-C3N4, we investigated the effect of exfoliation level on the piezocatalytic activity for degrading tetracycline hydrochloride (TC). Characterization results indicated that the specific surface area of the bulk g-C3N4 was much lower than those of exfoliated g-C3N4 samples due to the decrease of size and thickness. However, piezoresponse force microscopy (PFM) and kelvin probe force microscopy (KPFM) examinations suggested the bulk g-C3N4 possessed the biggest piezoelectric polarization that gradually declined as increasing the exfoliation temperature. Through testing the piezocatalytic abatement of TC, the activity decline following the order of decrease in polarization was confirmed, which demonstrated the piezoelectric polarization was the dominant factor in the piezocatalysis of g-C3N4. This conclusion was also verified by the step-by-step performance decrease of the bulk g-C3N4 during the successive four piezocatalytic runs, where the ultrasound treatment promoted the delamination of g-C3N4. In addition, superoxide (·O2−) radical, hydroxyl (·OH) radical and polarized positive charge were determined to be main active species, and accordingly the bulk g-C3N4 had the highest ·OH and ·O2− concentrations, as well as the highest piezocurrent response. This work reveals the main role to affect the piezocatalytic performance of g-C3N4, and also provides a possible strategy to design piezocatalysts with optimized piezocatalytic activity.

Piezoelectric ferromagnetism in Janus monolayer YBrI: a first-principles prediction.

Coexistence of intrinsic ferromagnetism and piezoelectricity, namely piezoelectric ferromagnetism (PFM), is crucial to advance multifunctional spintronic technologies. In this work, we demonstrate that Janus monolayer YBrI is a PFM, which is dynamically, mechanically and thermally stable. The electronic correlation effects on the physical properties of YBrI are investigated by using generalized gradient approximation plus U (GGA+U) approach. For out-of-plane magnetic anisotropy, YBrI is a ferrovalley (FV) material, and its valley splitting is larger than 82 meV within the considered U range. The anomalous valley Hall effect (AVHE) can be achieved under an in-plane electric field. However, for in-plane magnetic anisotropy, YBrI is a common ferromagnetic (FM) semiconductor. When considering intrinsic magnetic anisotropy, the easy axis of YBrI is always in-plane, and its magnetic anisotropy energy (MAE) varies from 0.309 meV to 0.237 meV (U = 0.0 eV to 3.0 eV). However, the magnetization can be adjusted from the in-plane to out-of-plane direction by an external magnetic field, and then lead to the occurrence of valley polarization. Moreover, the missing centrosymmetry along with broken mirror symmetry results in both in-plane and out-of-plane piezoelectricity in the YBrI monolayer. At a typical U = 2.0 eV, the piezoelectric strain coefficient d11 is predicted to be -5.61 pm V-1, which is higher than or comparable with the ones of other known two-dimensional (2D) materials. The electronic and piezoelectric properties of YBrI can be effectively tuned by applying biaxial strain. For example, tensile strain can enhance valley splitting and d11 (absolute value). The predicted magnetic transition temperature of YBrI is higher than those of experimentally synthesized 2D FM materials CrI3 and Cr2Ge2Te6. Our findings of these distinctive properties could pave the way for designing multifunctional spintronic devices, and bring forward a new perspective for constructing 2D materials.

Ternary pentagonal BXN (X = C, Si, Ge, and Sn) sheets with high piezoelectricity.

The discovery of new and stable two-dimensional pentagonal materials with piezoelectric properties is essential for technological advancement. Inspired by recently reported piezoelectric materials penta-BCN and penta-BSiN, we proposed penta-BGeN and penta-BSnN as new members of the penta-family based on first-principles calculations. Comprehensive analyses indicated that both penta-BGeN and penta-BSnN are thermodynamically, dynamically, mechanically, and thermally stable. In terms of mechanical stability, the elastic constant decreased as lower elements in group 4A of the periodic table were used. Therefore, penta-BGeN and penta-BSnN are softer than penta-BCN and penta-BSiN. In terms of piezoelectric properties, piezoelectric stress and strain tensors increase following the same pattern. In group 4A, penta-BSnN had the highest intrinsic piezoelectricity, especially the e 22 piezoelectric stress. Typically, the piezoelectric strain d ij coefficient increases with material softness; penta-BSnN possessed the highest d ij . Thus, due to its inherent piezoelectricity, penta-BSnN has tremendous potential as a nanoscale piezoelectric material.

Piezoelectric 1T Phase MoSe2 Nanoflowers and Crystallographically Textured Electrodes for Enhanced Low-Temperature Zinc-Ion Storage.

Transition metal dichalcogenides (TMDs) are regarded as promising cathode materials for zinc-ion storage owing to their large interlayer spacings. However, their capabilities are still limited by sluggish kinetics and inferior conductivities. In this study, a facile one-pot solvothermal method is exploited to vertically plant piezoelectric 1T MoSe2 nanoflowers on carbon cloth (CC) to fabricate crystallographically textured electrodes. The self-built-in electric field owing to the intrinsic piezoelectricity during the intercalation/deintercalation processes can serve as an additional piezo-electrochemical coupling accelerator to enhance the migration of Zn2+ . Moreover, the expanded interlayer distance (9-10Å), overall high hydrophilicity, and conductivity of the 1T phase MoSe2 also promoted the kinetics. These advantages endow the tailored 1T MoSe2 /CC nanopiezocomposite with feasible Zn2+ diffusion and desirable electrochemical performances at room and low temperatures. Moreover, 1T MoSe2 /CC-based quasi-solid-state zinc-ion batteries are constructed to evaluate the potential of the proposed material in low-temperature flexible energy storage devices. This work expounds the positive effect of intrinsic piezoelectricity of TMDs on Zn2+ migration and further explores the availabilities of TMDs in low-temperature wearable energy-storage devices.

Large tunable Rashba spin splitting and piezoelectric response in Janus chromium dichalcogenide monolayers

A mirror asymmetric Janus structure induces Rashba spin splitting (RSS) and a piezoelectric response. Inspired by the recently synthesized layered material CrSSe [Yang, Shi, Wang, Yue, Zheng, Zhang, Gu, Yang, Shadike, Li, and Fu, J. Mater. Chem. A 8, 25739 (2020)], we use first-principles calculations to systematically study the Rashba effect and piezoelectricity of Janus chromium dichalcogenide monolayers $\mathrm{Cr}XY$ ($X\ensuremath{\ne}Y=\text{S,}\phantom{\rule{4.pt}{0ex}}\text{Se,}\phantom{\rule{4.pt}{0ex}}\text{Te}$), as well as their regulation with biaxial strain. Our results reveal that spin-orbit coupling (SOC) plays an important role in the electronic properties (such as the semiconductor type, RSS, and valley polarization) of a $\mathrm{Cr}XY$ monolayer. Due to the mirror symmetry break and strong SOC, the strain-free $\mathrm{Cr}XY$ exhibits large Rashba parameters. Specifically, the Rashba parameter of CrSeTe is as high as 1.23 eV \AA{}. Due to the ${\mathit{k}}^{3}$ term in the valence-band edge, the CrSeTe exhibits a strong hexagonal warping effect along with a nonzero out-of-plane spin polarization ${\mathit{S}}_{z}$, which can also be found in the CrSSe and CrSTe monolayers in the lower energy valence bands. Moreover, the Janus $\mathrm{Cr}XY$ monolayer exhibits superior intrinsic piezoelectric responses (${\mathit{d}}_{31}$ = $0.4--0.83$ pm/V), which are orders of magnitude larger than those of the $\mathrm{Mo}XY$ monolayer. Furthermore, we reveal in detail the modulation of the band structure, RSS, and piezoelectric properties with biaxial strain. Tensile strain suppresses the band gap, whereas compressive strain increases the band gap. Thus, strain engineering can effectively tune the band structures resulting in semiconductor-metal and indirect-direct transitions. In addition, the strain has opposite effects on the RSS and the piezoelectricity; that is, unlike compressive strain-enhanced RSS, the tensile strain can significantly elevate the piezoelectric coefficients. Our results indicate that a Janus $\mathrm{Cr}XY$ monolayer has coexisting large intrinsic RSS and piezoelectricity, which can be efficiently regulated by strain engineering, opening opportunities for applications in spintronic and piezoelectric devices.

Origin of high piezoelectricity in CBT-based Aurivillius ferroelectrics: Glide of (Bi2O2)2+ blocks and suppressed internal bias field

This work investigates the substitution of Ce donor for Bi at A-site, which effectively improves the piezoelectricity and electrical resistivity of Aurivillius-phase CaBi4Ti4O15 (CBT) ceramic. Crystal structures of CaBi4-xCexTi4O15 ceramics are studied systematically, revealing the reason of unit cell contraction and the decreased ferro-distortion in crystal structure. The first-principles calculation shows that the enhancement of the intrinsic piezoelectricity in Ce-doped CBT ceramics come from the polarization stretching, where the translation and off-center displacement response under macroscopic strain of (Bi2O2)2+ layers playing an unexpectedly significant role. Ce doping can break the long-range ferroelectric chain, softening the flexibility of polarization and then making higher displacement response to strain for the other atoms, specially, the glide between the (Bi2O2)2+ layer and perovskite block is strong enhanced. Meanwhile, fewer defect dipoles (V″′Bi−VO••)dipolesin Ce-doped CBT ceramics result in a less internal bias field (Eib), which favors the polarization rotation and extension. Moreover, the significant role of oxygen vacancy ionization in electrical conductivity is inhibited, so both direct current resistance (ρdc) and activation energy of the charge carriers (Ea) are effectively enhanced in Ce-doped CBT ceramics.

Metal-Free Perovskite Piezoelectric Nanogenerators for Human-Machine Interfaces and Self-Powered Electrical Stimulation Applications.

Single crystal metal‐free halide perovskites have received great attention in recent years owing to their excellent piezoelectric and ferroelectric properties. However, the nanotoxicity and piezoelectricity within the nanoscale of such materials have yet been reported for the demonstration of practical applications. In this work, the observation of intrinsic piezoelectricity in metal‐free perovskite (MDABCO‐NH4I3) films using piezoresponse force microscopy (PFM) is reported. A cytotoxicity test is also performed on MDABCO‐NH4I3 to evaluate its low‐toxic nature. The as‐synthesized MDABCO‐NH4I3 is further integrated into a piezoelectric nanogenerator (PENG). The MDABCO‐NH4I3‐based PENG (MN‐PENG) exhibits optimal output voltage and current of 15.9 V and 54.5 nA, respectively. In addition, the MN‐PENG can serve as a self‐powered strain sensor for human–machine interface applications or be adopted in in vitro electrical stimulation devices. This work demonstrates a path of perovskite‐based PENG with high performance, low toxicity, and multifunctionality for future advanced wearable sensors and portable therapeutic systems.

Tungsten disulfide nanosheets for piezoelectric nanogenerator and human-machine interface applications

Tungsten disulfide (WS2), which is one of the most common transition metal dichalcogenides (TMDCs), has received great attention in recent years owing to their outstanding carrier mobility, chemical functionality, and optoelectronic properties. However, only few attempts have been reported to access its electromechanical characteristics. Herein, we investigate the intrinsic piezoelectricity of monolayer WS2 nanosheets (NSs) synthesized by chemical vapor deposition (CVD) and estimate their effective piezoelectric coefficient d33 by piezo-response force microscopy (PFM). Moreover, the as-grown WS2 NS was further fabricated into a piezoelectric nanogenerator (W-PENG) to evaluate their energy harvesting capability within nanoscale dimension. More importantly, the W-PENG was applied as self-powered strain sensors with high sensitivity, and integrated into a smart gesture recognition system. These results demonstrate that the W-PENG has great potential for future strain-modulated electronics, ultrathin functional sensors, and human-machine interface design.

Wafer-Scale Electroactive Nanoporous Silicon: Large and Fully Reversible Electrochemo-Mechanical Actuation in Aqueous Electrolytes.

Nanoporosity in silicon results in interface-dominated mechanics, fluidics, and photonics that are often superior to the ones of the bulk material. However, their active control, for example, by electronic stimuli, is challenging due to the absence of intrinsic piezoelectricity in the base material. Here, for large-scale nanoporous silicon cantilevers wetted by aqueous electrolytes, electrosorption-induced mechanical stress generation of up to 600 kPa that is reversible and adjustable at will by potential variations of ≈1 V is shown. Laser cantilever bending experiments in combination with in operando voltammetry and step coulombmetry allow this large electro-actuation to be traced to the concerted action of 100 billions of parallel nanopores per square centimeter cross-section and determination of the capacitive charge-stress coupling parameter upon ion adsorption and desorption as well as the intimately related stress actuation dynamics for perchloric and isotonic saline solutions. A comparison with planar silicon surfaces reveals mechanistic insights on the observed electrocapillarity (Hellmann-Feynman interactions) with respect to the importance of oxide formation and wall roughness on the single-nanopore scale. The observation of robust electrochemo-mechanical actuation in a mainstream semiconductor with wafer-scale, self-organized nanoporosity opens up novel opportunities for on-chip integrated stress generation and actuorics at exceptionally low operationvoltages.

Coexistence of intrinsic piezoelectricity, ferromagnetism, and nontrivial band topology in Li-decorated Janus monolayer Fe2SSe with a high Curie temperature

Recently, predictions have been made about quantum anomalous Hall (QAH) insulators in Lithium-decorated iron-based superconductor monolayer materials (LiFeX (X = S, Se and Te)) with very high Curie temperatures (0.00,0.00,1.00PRL 125, 086401 (2020)), which combine topological and ferromagnetic orders. It is interesting and useful to achieve the coexistence of intrinsic piezoelectricity, ferromagnetism, and nontrivial band topology in single two-dimensional (2D) materials, namely 2D piezoelectric quantum anomalous Hall insulators (PQAHIs). In this work, 2D Janus monolayer Li2Fe2SSe is predicted to be a room-temperature PQAHI, which possesses dynamic, mechanical, and thermal stabilities. It is predicted to be a half Dirac semimetal without spin–orbit coupling (SOC). It is found that the inclusion of SOC opens up a large nontrivial gap, which means nontrivial bulk topology (QAH insulator), confirmed by the calculation of Berry curvature and the presence of two chiral edge states (Chern number C = 2). Calculated results show that the monolayer Li2Fe2SSe possesses robust QAH states against biaxial strain and electronic correlations. Compared to LiFeX, the glide mirror G z of Li2Fe2SSe disappears, which will only induce an out-of-plane piezoelectric response. The calculated out-of-plane d 31 of the monolayer Li2Fe2SSe is −0.238 pm V−1, comparable with those of other known 2D materials. Moreover, a very high Curie temperature (about 1000 K) is predicted by using Monte Carlo simulations, which means that the QAH effect can be achieved at room temperature in the Janus monolayer Li2Fe2SSe. Similar to the monolayer Li2Fe2SSe, the PQAHI can also be realized in the Janus monolayer Li2Fe2SeTe. Our work opens a new avenue in searching for PQAHIs with high temperatures and high Chern numbers, which provide a potential platform for multi-functional spintronic applications.