Switching Barriers Research Articles

Two-Dimensional Topological Ferroelectric Metal with Giant Shift Current.

The pursuit for "ferroelectric metal," which combines seemingly incompatible spontaneous electric polarization and metallicity, has been assiduously ongoing but remains elusive. Unlike traditional ferroelectrics with a wide band gap, ferroelectric (FE) metals can naturally incorporate nontrivial band topology near the Fermi level, endowing them with additional exotic properties. Here, we show first-principles evidence that the metallic PtBi_{2} monolayer is an intrinsic two-dimensional (2D) topological FE metal, characterized by out-of-plane polarization and a moderate switching barrier. Moreover, it exhibits a topologically nontrivial electronic structure with Z_{2} invariant equal to 1, leading to a significant FE bulk photovoltaic effect. A slight strain can further enhance this effect to a remarkable level, which far surpasses that of previously reported 2D and 3D FE materials. Our Letter provides an important step toward realizing intrinsic monolayer topological FE metals and paves a promising way for future nonlinear optical devices.

Visible-Photo-Assisted Phase Switching of Antiferroelectric-to-Ferroelectric Orders in an I3 --Intercalated 2D Perovskite.

Antiferroelectric (AFE) has emerged as a promising branch of electroactive materials, due to intriguing physical attributes stemming from the electric field-induced antipolar-to-polar phase transformation. However, the requirement of extremely high electric field strength to switch adjacent sublattice polarization poses great challenges for exploiting new molecular AFE system. Although photoirradiation is striking as a noncontact and nondestructive manipulation tool to optimize physical properties, optical control of antiferroelectricity still remains unexplored. Here, by adopting light-sensitive I3 - anion into 2D perovskite family, we design a new I3 --intercalated molecular AFE of (t-ACH)2EA2Pb3I10(I3)0.5 ⋅ ((H3O)(H2O))0.5 (1, t-ACH=trans-4-aminomethyl-1-cyclohexanecarboxylate, EA=ethylammonium). The I3 --intercalating gives an ultra-narrow band gap of 1.65 eV with strong absorption. In term of AFE structure, the anti-parallel alignment of electric dipoles results in a large spontaneous polarization of 4.3 μC/cm2. Strikingly, 1 merely shows AFE behaviour in the dark even under ultrahigh voltage, while the field-induced ferroelectric state can be facilely obtained upon visible illumination. Such unprecedented visible-photo-assisted phase switching ascribes to the incorporation of photoactive I3 - anions that reduces AFE-to-ferroelectric switching barrier. This pioneering work on the photo-assisting transformation of ferroic orders paves a way to develop future photoactive materials with potential applications.

Visible‐Photo‐Assisted Phase Switching of Antiferroelectric‐to‐Ferroelectric Orders in an I3−‐Intercalated 2D Perovskite

AbstractAntiferroelectric (AFE) has emerged as a promising branch of electroactive materials, due to intriguing physical attributes stemming from the electric field‐induced antipolar‐to‐polar phase transformation. However, the requirement of extremely high electric field strength to switch adjacent sublattice polarization poses great challenges for exploiting new molecular AFE system. Although photoirradiation is striking as a noncontact and nondestructive manipulation tool to optimize physical properties, optical control of antiferroelectricity still remains unexplored. Here, by adopting light‐sensitive I3− anion into 2D perovskite family, we design a new I3−‐intercalated molecular AFE of (t‐ACH)2EA2Pb3I10(I3)0.5 ⋅ ((H3O)(H2O))0.5 (1, t‐ACH=trans‐4‐aminomethyl‐1‐cyclohexanecarboxylate, EA=ethylammonium). The I3−‐intercalating gives an ultra‐narrow band gap of 1.65 eV with strong absorption. In term of AFE structure, the anti‐parallel alignment of electric dipoles results in a large spontaneous polarization of 4.3 μC/cm2. Strikingly, 1 merely shows AFE behaviour in the dark even under ultrahigh voltage, while the field‐induced ferroelectric state can be facilely obtained upon visible illumination. Such unprecedented visible‐photo‐assisted phase switching ascribes to the incorporation of photoactive I3− anions that reduces AFE‐to‐ferroelectric switching barrier. This pioneering work on the photo‐assisting transformation of ferroic orders paves a way to develop future photoactive materials with potential applications.

Universal Polar Instability in Highly Orthorhombic Perovskites.

The design of novel multiferroic ABO3 perovskites is complicated by the presence of necessary magnetic cations and ubiquitous antiferrodistortive modes, both of which suppress polar distortions. Using first-principles simulations, we observe that the existence of quadlinear and trilinear invariants in the free energy, coupling tilts, and antipolar motions of A and B sites to the polar mode drives an avalanche-like transition to a non-centrosymmetric Pna21 symmetry in a wide range of magnetic perovskites with small tolerance factors, overcoming the above restrictions. We find that the Pna21 phase is especially favored with tensile epitaxial strain, leading to an unexpected but technologically useful out-of-plane polarization. We use this mechanism to predict various novel multiferroics, displaying interesting magnetoelectric properties with small polarization switching barriers.

High and temperature-stable electrostrain in lead-free environmentally friendly BiFeO3-BaTiO3 piezoelectric ceramics

Currently, environmental pollution and industrial effluents are depleting soil, water, and aquatic life and pose serious concerns to climate change. Environmentally friendly piezoelectric materials are considered potential agents for industrial applications, as they can generate clean energy by applying mechanical forces. High and temperature-insensitive piezoelectric strain is an ever-increasing demand in lead-free ceramics. In this work, a lead-free La-doped BiFeO3-BaTiO3 composition is designed at the crossover boundary of normal-relaxor ferroelectrics. The properties are optimized as a function of sintering temperature (Ts) from 960 to 1000 °C. An enhanced and thermally stable converse piezoelectric constant (d33∗) of 760 ± 23 pm/V over a wide range of 25–150 °C is achieved at an optimized TS of 980 °C. This high electrostrain response is mainly attributed to the low energy barrier for domain switching due to multiple-point crystal structure morphotropic phase boundary. Additionally, the high Curie temperature (TC) of 355 °C with excellent piezoelectric strain performance of our work are promising results for high-temperature piezoelectric actuators. The framework of chemical composition design and phase engineering of this work could inspire further development of lead-free ceramics for industrial applications.

Demonstration of 1 V Reliable FeRAM Operation: Vc Engineering Using Quasi-Chirality of Hf1-xZrxO2 in a Nanolaminate Structure.

Hafnia thin films are known to demonstrate excellent performance with strong ferroelectricity and high scalability, making them promising candidates for CMOS-compatible materials. However, the reliability of ferroelectric devices must be further improved. This study developed a Hf1-xZrxO2 ferroelectric capacitor with a nanolaminate structure that operated at remarkably low voltages, demonstrating excellent retention (>10 years/85 °C) and endurance (>1010 cycles). The exceptional performance is attributed to the presence of thin tetragonal phase layers within the thick ferroelectric layers, which decreased the switching barrier in the nanolaminate films. Further, we verified phase crystallization via a detailed analysis of high-resolution transmission electron microscopy images. The improved switching propagation in the nanolaminate films was confirmed through switching speed measurements and theoretical models. Furthermore, we addressed pinching issues by precisely controlling the Hf/Zr ratio and O3 treatment. The initial imprint and retention characteristics were improved by interfacial engineering. Moreover, by reducing the thickness, we have achieved reliable operation at 1.0 V with a 5.5 nm-thick device while maintaining high retention and endurance. This study is a significant step toward the realization of the longstanding problem of ferroelectric random access memory operation voltage with respect to endurance and retention characteristics.

SPORTS CLUB LOYALTY: GENERAL AND AGE-RELATED ANALYSIS. AN EXAMPLE FROM RECREATIONAL RIDERS IN RIDING SCHOOL

Objective: The objective of this study is to investigate the impact of age on sporting club loyalty, focusing on horse riding in France. Theoretical Framework: Using a consumer behavior marketing approach, this study provides an understanding of the relationships and influence between the constructs of loyalty, satisfaction, switching barriers, affective commitment to the group of friends and community commitment. Method: A multigroup SEM was used to provide a global understanding. The Data collection was carried out through on online survey amongst 615 respondents in France. Results and Discussion: Whatever the age is, the results confirm the classical influence of satisfaction on loyalty and highlight the significant influence of riding teachers on customer loyalty to riding schools. The relationships between the other constructs differ by age with different factors influencing satisfaction and loyalty. Younger riders’ loyalty relies more on teacher linkage, while older riders consider a more global environment, including switching barriers and commitments. Research Implications: The practical and theoretical implications of this research are discussed, providing insights into how the results can be applied or influence practices in the field of sport management. These implications could encompass equestrian activities and sports businesses. Originality/Value: This study contributes to the literature by showing the differences or correlations between segments of recreational riders according to their loyalty to their riding club. Thus, adapting marketing and management strategies according to the age of recreational riders is essential to improve loyalty according to its main drivers.

Intrinsically Stable Charged Domain Walls in Molecular Ferroelectric Thin Films

AbstractCharged domain walls in ferroelectrics hold great promise for applications in ferroelectric random‐access memory (FeRAM), with advantages such as low energy consumption, high density, and non‐destructive operation. Due to the mechanical compatibility condition, the neutral domain walls are dominant in traditional ferroelectric thin films. Herein, using phase‐field simulations, the formation of intrinsically stable charged domain walls (CDWs) in the molecular ferroelectric films is demonstrated, which can be mainly attributed to the small mechanical stiffness. The switching kinetics are further investigated for the CDWs, showing a lower switching barrier as compared to the neutral counterparts. Moreover, it is indicated that increasing the compressive misfit strain can lead to prolonged switching time, with a significantly increased switching energy barrier. These findings pave the way for the potential applications of metal‐free organic ferroelectric materials in FeRAM devices.

Two-dimensional ferroelastic semiconductors InXY (X = S, Se; Y = Cl, Br, I): Promising candidates for photocatalytic water splitting with tunable electronic anisotropy

We have identified a class of two-dimensional ferroelastic monolayers, denoted as InXY (where X = S, Se; Y = Cl, Br, I), through first-principles calculations. The dynamic, thermal, and mechanical stabilities of these InXY monolayers are validated by phonon dispersion spectra, AIMD calculations, and elastic constants, respectively. These monolayers exhibit semiconducting behavior with bandgaps ranging from 1.94 to 2.85 eV and possess excellent ferroelasticity with strong ferroelastic signals and moderate ferroelastic switching barriers. Notably, the band edge positions of InSBr and InSI monolayers are observed to stride the water redox potentials at pH = 0, indicating their potential as photocatalysts for water splitting in acidic environments. We also explored the effects of biaxial strain on the band edge alignments and photocatalytic performance of these monolayers. Moreover, the InXY monolayers exhibit excellent anisotropic optical absorption across the visible to ultraviolet regions, along with high anisotropic carrier transport. The coupling of ferroelastic and anisotropic properties in these monolayers offers promising opportunities for designing controllable electronic devices, thereby expanding their potential applications in multifunctional materials. Our findings reveal that the InXY monolayers are promising candidates for efficient photocatalytic water splitting and controllable optoelectronic applications.

명품 화장품에 대한 관계혜택이 전환장벽과 브랜드 충성도에 미치는 영향 - 온라인 및 오프라인 소매업태의 조절효과를 중심으로

This research explores the impact of relational benefits, which are the advantages gained from a sustained relationship with a specific brand, on switching barriers and brand loyalty among female consumers aged 20 to 50 residing in China when purchasing luxury cosmetics. The research analyzes the influence difference between different retail formats online and offline, aiming to reveal the shifting psychological dynamics of consumers amid the latest changes in China's consumer market. Using SPSS and AMOS programs, data from 500 participants were analyzed, with a focus on seven types of relational benefits: experiential benefits, confidence benefits, special treatment benefits, convenience benefits, economic benefits, information benefits and risk reduction benefits. The results indicate that relational benefits significantly enhance switching barriers and brand loyalty, and these effects vary distinctly between online and offline retail channels. The findings offer valuable insights for luxury cosmetic brands to formulate effective strategies in the Chinese market.

Forever I am yours: the interrelationship between service brand love, psychological contracts and customer switching barriers in the banking industry

PurposeThis study aims to examine the influence of dimensions of the psychological contract on strengthening customers' switching barriers through the mediating role of service brand love.Design/methodology/approachThe study used a cross-sectional survey research design to collect data from 406 respondents from commercial banks in the banking industry. A quantitative approach using structural equation modeling was used to analyze the data collected through structured questionnaires.FindingsThe findings revealed that dimensions of the psychological contract, namely, ideological, transactional and relational psychological contract, significantly influence the strengthening of customers' switching barriers when mediated by service brand love.Practical implicationsManagers should consider adopting high-intensity relationship approaches that go beyond mere customer satisfaction to ensure customer retention.Originality/valueWhile customer retention remains the primary avenue for establishing competitive advantages, there remain unresolved issues regarding what determines customers’ intentions to stay or switch. This study represents one of the initial endeavors to explore the psychological contract within the context of the service industry. It contributes to the existing knowledge by enhancing the understanding of the mechanisms that can impact customers' switching barriers and complements the literature on customer retention in the service domain.

First-principles prediction of ferroelectricity in defective wurtzite α-Ga2S3

Abstract Wurtzite-type ferroelectrics have attracted much attention as next generation ferroelectric materials due to high spontaneous polarizations. However, wurtzite-type ferroelectrics require high electric fields to switch their polarization direction, resulting in small margins with breakdown electric fields. To address this issue, considerable efforts have been made to explore wurtzite ferroelectrics with moderate switching barriers. In this study, our first-principles calculations have predicted the ferroelectricity of defective wurtzite α-Ga2S3. The calculated polarization is 60 μC/cm2, which is comparable to or smaller than those of conventional wurtzite ferroelectrics. The minimum energy pathway associated with the polarization switching reveals a moderate switching barrier of 67 meV/atom. The energy landscape for α-Ga2S3 is quite different from that for its isostructural Al-based counterpart α-Al2S3, which our recent theoretical study has predicted to have quadruple-well ferroelectricity. The difference in chemical bonding between cations and sulfide ions accounts for their different energy landscapes for polarization switching.

Modulation of Polarization in Sliding Ferroelectrics by Introducing Intrinsic Electric Fields.

The emergence of sliding ferroelectricity facilitates low-barrier ferroelectrics in two-dimensional materials, while limited electric polarizations impede practical applications. Herein, we propose an effective strategy to enlarge the polarization by introducing an intrinsic electric field, exemplified by Janus transition metal dichalcogenides (TMDs) with the first-principle calculations. The intrinsic electric field is introduced and regulated by leveraging the electronegativity differences among chalcogens. An improved polarization is achieved in the Janus TeMoS bilayer with a polarization of 1.18 pC/m, a 65% enhancement compared to normal TMD bilayers. Through differential charge density analysis, the inner mechanism is attributed to the effects of intrinsic electric fields on charge redistribution. Furthermore, the feasibility of polarization reversal is determined by evaluating switching barriers and the responses under an electric field. The provided proposal is applicable and available for broader systems and will pave the way for the development of novel electronic devices.

Magnetization Switching of Single Magnetite Nanoparticles Monitored Optically.

Magnetic nanomaterials record information as fast as picoseconds in computer memories but retain it for millions of years in ancient rocks. This exceedingly broad range of times is covered by hopping over a potential energy barrier through temperature, ultrafast optical excitation, mechanical stress, or microwaves. As switching depends on nanoparticle size, shape, orientation, and material properties, only single-nanoparticle studies can eliminate the ensemble heterogeneity. Here, we push the sensitivity of photothermal magnetic circular dichroism down to individual 20 nm magnetite nanoparticles. Single-particle magnetization curves display superparamagnetic to ferromagnetic behaviors, depending on the size, shape, and orientation. Some nanoparticles undergo thermally activated switching on time scales of milliseconds to minutes. Surprisingly, the switching barrier varies with time, leading to dynamical heterogeneity, a phenomenon familiar in protein dynamics and supercooled liquids. Our observations will help to identify the external parameters influencing magnetization switching and, eventually, to control it, an important step for many applications.

Defects and oxygen impurities in ferroelectric wurtzite Al1−xScxN alloys

III-nitrides and related alloys are widely used for optoelectronics and as acoustic resonators. Ferroelectric wurtzite nitrides are of particular interest because of their potential for direct integration with Si and wide bandgap semiconductors and unique polarization switching characteristics; such interest has taken off since the first report of ferroelectric Al1−xScxN alloys. However, the coercive fields needed to switch polarization are on the order of MV/cm, which are 1–2 orders of magnitude larger than oxide perovskite ferroelectrics. Atomic-scale point defects are known to impact the dielectric properties, including breakdown fields and leakage currents, as well as ferroelectric switching. However, very little is known about the native defects and impurities in Al1−xScxN and their effect on the dielectric and ferroelectric properties. In this study, we use first-principles calculations to determine the formation energetics of native defects and unintentional oxygen incorporation and their effects on the polarization switching barriers in Al1−xScxN alloys. We find that nitrogen vacancies are the dominant native defects, and unintentional oxygen incorporation on the nitrogen site is present in high concentrations. They introduce multiple mid-gap states that can lead to premature dielectric breakdown and increased temperature-activated leakage currents in ferroelectrics. We also find that nitrogen vacancy and substitutional oxygen reduce the switching barrier in Al1−xScxN at low Sc compositions. The effect is minimal or even negative (increases barrier) at higher Sc compositions. Unintentional defects are generally considered to adversely affect ferroelectric properties, but our findings reveal that controlled introduction of point defects by tuning synthesis conditions can instead benefit polarization switching in ferroelectric Al1−xScxN at certain compositions.

In-Plane Sliding Ferroelectricity Realized in Penta-PdSe2/Penta-PtSe2 van der Waals Heterostructure.

Different from conventional 2D sliding ferroelectrics with polarization switchable in the out-of-plane via interlayer sliding, we show the existence of in-plane sliding ferroelectricity in a bilayer of a pentagon-based van der Waals heterostructure formed by vertically stacking an experimentally synthesized penta-PdSe2 sheet and a crystal lattice well-matched penta-PtSe2 sheet. From the 128 sliding patterns, four stable configurations are found that exhibit in-plane sliding ferroelectricity with an ultralow polarization switching barrier of 1.91 meV/atom and a high ferroelectric polarization of ±17.11 × 10-10 C m-1. Following the ferroelectric transition among the stable sliding configurations, significant changes in carrier mobility, electrical conductivity, and second harmonic generation are identified. In particular, the ferroelectric stacking configurations are found to possess a negative Poisson's ratio, facilitating the experimental characterization of the sliding ferroelectric effect. This study demonstrates that pentagonal sheets can be used to realize 2D in-plane sliding ferroelectrics going beyond the existing ones.

Insights into enhanced antiferroelectricity in doped-niobate perovskites for high energy-storage density applications

Lead-free antiferroelectric (AFE) ceramics have attracted increasing attention in recent years for application in high-power capacitors due to their environmental friendliness and high energy density. Among these ceramics, NaNbO3 is noteworthy as one of the few lead-free perovskites displaying an AFE structure. However, despite the nature of AFE symmetry in NaNbO3 with Nb antipolar state, in most cases, it behaves like a ferroelectric (FE) material with an external electric field and exhibits a single polarization-electric field (P-E) hysteresis loop. In order to enhance the antiferroelectricity, a composition modification strategy based on the tolerance factor (t) has been used to stabilize the AFE phase effectively. Yet, in the context of NaNbO3 ceramics, the impact of doping on the evolution of antiferroelectricity has remained unexplored. Through first-principles calculations, we unveil how the chemical modification of NaNbO3 enhances antiferroelectricity by investigating local distortions that favor the AFE state over the FE state in solid solutions. This adjustment in the relative stability between the FE state and AFE state results in a significant modification in the switching barrier in NaNbO3-based antiferroelectrics, ultimately leading to well-defined double polarization loops. This work offers a rationalized atomic-scale perspective on the AFE-FE phase transition in NaNbO3-based ceramics, aiming to contribute to the development of novel lead-free antiferroelectric oxides for energy storage applications.

Switching it up: New mechanisms revealed in wurtzite-type ferroelectrics.

Wurtzite-type ferroelectrics have drawn increasing attention due to the promise of better performance and integration than traditional oxide ferroelectrics with semiconductors such as Si, SiC, and III-V compounds. However, wurtzite-type ferroelectrics generally require enormous electric fields, approaching breakdown, to reverse their polarization. The underlying switching mechanism(s), especially for multinary compounds and alloys, remains elusive. Here, we examine the switching behaviors in Al1-xScxN alloys and wurtzite-type multinary candidate compounds we recently computationally identified. We find that switching in these tetrahedrally coordinated materials proceeds via a variety of nonpolar intermediate structures and that switching barriers are dominated by the more-electronegative cations. For Al1-xScxN alloys, we find that the switching pathway changes from a collective mechanism to a lower-barrier mechanism enabled by inversion of individual tetrahedra with increased Sc composition. Our findings provide insights for future engineering and realization of wurtzite-type materials and open a door to understanding domain motion.

Ferroelectricity with Long ion Displacements in Crystals of Non‐Polar Point Groups

AbstractIn the classical model, ferroelectricity is associated with small ion displacements from paraelectric phases with high symmetry, and ferroelectric crystals must adopt one of the ten polar point groups with low symmetry according to Neumann's principle. In this work, it is proposed that this conclusion is based on perfect bulk crystals without taking the boundaries into account. First‐principles evidence shows that ferroelectric polarizations may also be formed in some non‐polar point groups as the edges generally break the crystal symmetry. Meanwhile, such polarizations can be maintained at macroscale and are switchable when the transition between multiple equivalent states with high symmetry can be realized via long ion displacements， essentially akin to ion conductors. For example, the switching barriers can be much reduced in sliding ferroelectric bilayer systems or ionic compounds with covalent‐like directionality. Such unconventional ferroelectricity can be attributed to the boundaries and long ion displacements, and its existence in several systems like CuCrS2 is supported by experimental observations. It may explain a series of unclarified phenomena reported previously as well as significantly expand the scope of ferroelectrics, especially those with high polarizations induced by long ion displacements.

Atomic-level polarization reversal in sliding ferroelectric semiconductors

Intriguing “slidetronics” has been reported in van der Waals (vdW) layered non-centrosymmetric materials and newly-emerging artificially-tuned twisted moiré superlattices, but correlative experiments that spatially track the interlayer sliding dynamics at atomic-level remain elusive. Here, we address the decisive challenge to in-situ trace the atomic-level interlayer sliding and the induced polarization reversal in vdW-layered yttrium-doped γ-InSe, step by step and atom by atom. We directly observe the real-time interlayer sliding by a 1/3-unit cell along the armchair direction, corresponding to vertical polarization reversal. The sliding driven only by low energetic electron-beam illumination suggests rather low switching barriers. Additionally, we propose a new sliding mechanism that supports the observed reversal pathway, i.e., two bilayer units slide towards each other simultaneously. Our insights into the polarization reversal via the atomic-scale interlayer sliding provide a momentous initial progress for the ongoing and future research on sliding ferroelectrics towards non-volatile storages or ferroelectric field-effect transistors.