Effect In Ferroelectric Materials Research Articles

Observation of converse flexoelectric effect in topological semimetals

A strong coupling between electric polarization and elastic deformation in solids is an important factor in creating useful electromechanical nanodevices. Such coupling is typically allowed in insulating materials with inversion symmetry breaking as exemplified by the piezoelectric effect in ferroelectric materials. Therefore, materials with metallicity and centrosymmetry have tended to be out of scope in this perspective. Here, we report the observation of giant elastic deformation by the application of an alternating electric current in topological semimetals (V,Mo)Te2, regardless of the centrosymmetry. Considering the crystal and band structures and the asymmetric measurement configurations in addition to the absence of the electromechanical effect in a trivial semimetal TiTe2, the observed effect is discussed in terms of a Berry-phase-derived converse flexoelectric effect in metals. The observation of the flexoelectric effect in topological semimetals paves a way for a new type of nanoscale electromechanical sensors and energy harvesting.

Negative slope polarization in ferroelectric hysteresis loop engineered by defect dipoles

The power dissipation in conventional microelectronic devices is facing a fundamental barrier of Boltzmann Tyranny. The negative capacitance (NC) effect in ferroelectric materials provides possible solution to overcome this impending problem and gets a lot of attention. Here we report a novel method to design negative capacitance in ferroelectrics by the introduction of defect-dipole engineering. In the molecular dynamics simulations of a first principles-based effective Hamiltonian, an abnormal polarization with negative slope and corresponding differential capacitance are observed in the polarization-electric field (P-E) hysteresis loops when the applied electric field is perpendicular to the direction of the defect dipoles in acceptor-doped BaTiO3 single crystals. This phenomenon is attributed to the fact that the polarization overshoots, oscillates and finally gradually switches to the direction of defect dipoles by their restoring forces during the polarization switching near the coercive field. The P-E loop exhibits abnormal NC response only at a certain range of defect levels, and there are double loops at high level and typical square-shaped loops at low level. Moreover, in the experiments of poled 1 mol.% Mn-doped BaTiO3 ceramics, the abnormal negative slope polarization in P-E loops is confirmed, which are in good agreement with the simulation results.

Enhanced energy storage performance in Bi4Ti3O12 thin films with oxygen depletion layers

The imprint effect in ferroelectric materials can significantly enhance the performance of energy storage devices. Bi4Ti3O12 (BTO) and oxygen-deficient Bi4Ti3O11.2 (DBTO) thin films were deposited on single-crystal Nb-doped SrTiO3 substrates using pulsed laser deposition. In stark contrast, multilayer DBTO/BTO thin films incorporating an oxygen-deficient layer were also fabricated, with the DBTO layers having thicknesses of 5 nm and 10 nm, respectively. Both BTO and DBTO thin films exhibited epitaxial growth and c-axis-oriented crystallinity. Regarding ferroelectric properties, DBTO/BTO capacitors with an oxygen-deficient layer demonstrated a pronounced imprint effect in their ferroelectric hysteresis loops, compared to the BTO and DBTO capacitors. This effect was particularly noticeable in the DBTO/BTO capacitor with a 10 nm oxygen-deficient layer, as opposed to the thin film with a 5 nm oxygen-deficient layer. We suggest that the imprint effect can be attributed to localized electric field variations and imbalances in charge transport at the interface between the oxygen-depleted layer and the remaining thin film. Consequently, the imprint effect observed in the DBTO/BTO capacitors contributed to an enhancement in energy storage density and efficiency, compared to BTO and DBTO capacitors. This study demonstrates the potential of multilayer DBTO/BTO thin films in advancing capacitive energy storage systems.

Mathematical analysis of the dynamics of solitary wave solutions to the time-fractional thin-film ferroelectric materials model

The thin-film ferroelectric materials equation is a fundamental mathematical model to explain the behavior of polarized electric fields in ferroelectric materials possessing unique properties such as piezoelectricity, pyroelectricity, electrostriction, hysteresis, spontaneous polarization, etc. These significant properties of ferroelectric materials are important in the progress of capacitors, non-volatile memories, electrical sensors, as well as optical and biomedical devices, among other applications. The aim of the present study is to explore applicable soliton solutions to the fractional-order model to the aforementioned equation by addressing the improved F-expansion method. Through analysis and rigorous identification, various radical solutions, including trigonometric, hyperbolic, and rational forms of the model, are established, and significant solitons are restored by setting appropriate parameter values in the analytical solutions obtained, which are demonstrated through 3D, 2D, and contour plots. We also explore the impact of fractional derivative as well as the parameters, like pressure, temperature, and others included in the model to determine the polarization effect in ferroelectric materials. This study uncovers several novel solutions along with their states in response to external or internal field parameters, which might be helpful in understanding the nature of ferroelectric materials.

The Effect of Multi-Fields Synergy from Electric/Light/Thermal/Force Technologies on Photovoltaic Performance of Ba0.06Bi0.47Na0.47TiO3 Ferroelectric Ceramics via the Mg/Co Substitution at A/B Sites.

Currently, it is widely reported that the photovoltaic effect in ferroelectric materials can be promoted by the application of a piezoelectric force, an external electric field, and intense light illumination. Here, a semiconducting ferroelectric composition is introduced, (1-x) Ba0.06Bi0.47Na0.47TiO3-xMgCoO3 (abbreviated as xMgCo, where x=0.02-0.08), synthesized through Mg/Co ions codoping. This process effectively narrows the optical bandgaps to a spectrum of 1.38-3.06eV. Notably, the system exhibits a substantial increase in short-circuit photocurrent density (Jsc), by the synergy of the electric, light, and thermal fields. The Jsc can still be further enhanced by the extra introduction of a force field. Additionally, the Jsc also shows an obvious increase after the high field pre-poling. The generation of a considerable number of oxygen vacancies due to the Co2+/Co3+ mixed valence state (in a 1:3 ratio) contributes to the reduced optimal bandgap. The integration of Mg2+ ion at the A-site restrains the loss and sustains robust ferroelectricity (Pr=24.1µCcm-2), high polarizability under an electric field, and a significant piezoelectric coefficient (d33=102pCN-1). This study provides a novel perspective on the physical phenomena arising from the synergy of multiple fields in ferroelectric photovoltaic materials.

Enhanced photocatalytic degradation performance of layered Ag-Bi4Ti3O12 plasmon resonance-coupled piezoelectric effect

Piezoelectric effects in ferroelectric materials arise from generating an internal electric field when subjected to mechanical stress, greatly facilitating the separation of photo-generated charge carriers in photocatalytic processes. However, it faces limitations such as inadequate conductivity and a restricted number of active sites. In this study, we successfully synthesized Ag-Bi4Ti3O12(Ag-BTO) composite piezoelectric photocatalysts using a molten salt method. By harnessing the synergistic combination of the piezoelectric effect and localized surface plasmon resonance, we achieved enhanced efficiency in photocatalytic processes. Optimizing the loading ratio of Ag, we achieved complete degradation of Rhodamine B (RhB) within a concise duration of 6 min, with degradation rates 1.867 times and 5.907 times higher than those observed for pure photocatalysis and piezoelectric catalysis, respectively. This research provides an illustrative approach for natural light and different piezoelectric driving forces for environmental remediation and imparts valuable insights for the design of highly efficient piezoelectric photocatalysts.

Bandgap modulation and phase boundary region of multiferroic Gd, Co co-doped BiFeO3 thin film

Ferroelectric polarization is a crucial factor to induce photovoltaic effect in ferroelectric materials. Here, a novel modulation of bandgap by Gd and Co co-doped BFO is found for a polycrystalline Bi0.9Gd0.1Fe0.85Co0.15O3 thin film prepared by the sol–gel process. The ferroelectric properties, magnetic properties, and bandgap of the BFO films were altered by doping Gd and Co. This work has led to a greater understanding of bismuth ferrate, and it proposes the Bi0.9Gd0.1Fe0.85Co0.15O3 thin film for the possibility of better preparation of high conversion efficiency ferroelectric photovoltaic devices.

Enhanced Photocurrent in Ferroelectric KNNS-BNN Materials via Temperature Modulation

The photocurrent produced by the synergy of pyroelectric and photovoltaic effects in ferroelectric materials exhibits great potential for photodetection. Photocurrent generated by various ferroelectric materials exhibits a different behavior with the ambient circumstance especially the temperature, making it a long-term topic. Here, we report a remarkable promotion in the photocurrent of a photoelectric device based on ferroelectric (K0.5Na0.5)(Nb0.94Sb0.06)O3-Bi(Ni0.33Nb0.67)O3 (KNNS-BNN) materials via temperature modulation. When compared with the photocurrents obtained at room temperature, by lowering the atmospheric temperature to 14.8 °C, the peak photocurrent is increased by 219%, and by raising the temperature to 46 °C, the platform photocurrent is improved by 69.9%. The enhanced photocurrents are mainly ascribed to temperature-controlled conductivity and energy band structure of the KNNS-BNN materials. Working as a self-powered photodetector, the responsivity of the device reaches 4.01 × 10–6 A W–1. This work provides new possibilities for high-performance ferroelectric photodetectors.

Flexoelectric aging effect in ferroelectric materials

In spite of the flexoelectric effect being a universal phenomenon in the ferroelectric perovskites, the current understanding of flexoelectric aging in ferroelectrics is, actually, rather incomplete. In this paper, we have fabricated a series of Mn-doped BaTiO3 perovskite ceramics (BaTi1–xMnxO3, x = 0.1% and 1%, BTMO) to systematically investigate the corresponding flexoelectric aging behavior by controlling the concentration of Mn. We found that the variation of Mn dopant significantly effects the Curie temperature, dielectric constant, flexoelectric aging, and flexoelectric coefficient of the BTMO ceramics. Especially for the BTMO (0.1%) ceramics, obvious ferroelectric aging and flexoelectric aging phenomenon are observed at room temperature. The main reason for aging of BTMO ceramics is that the doping of Mn introduces oxygen vacancies, which tend to be stable under the action of strain gradient and electric field. Therefore, the results presented in this paper verify that the flexoelectric aging in Mn-doped BTO ceramics is closely related to ferroelectric fatigue.

Theoretical insight of origin of Rashba-Dresselhaus effect in tetragonal and rhombohedral phases of BiFeO3.

The inclusion of the spin-orbit coupling effect in ferroelectric materials with non-centrosymmetry leads to intriguing properties for spintronic applications. In the present work, a comparative study of spin splitting in the bulk electronic energy bands of the tetragonal and rhombohedral phases of BiFeO3 (BFO) in terms of the Rashba and Dresselhaus effects is carried out through first-principles calculations. The obtained spin splittings, particularly at the conduction band minima, are further supplemented with an effective k·p model analysis. For the tetragonal BFO, a dominating pure bulk-type Rashba effect with helical in-plane spin components shown through diagrams is observed, whereas the rhombohedral BFO shows a significant contribution from the out-of-plane spin components and an interplay between the Rashba and Dresselhaus effects is discussed. In addition, tunability of the Rashba parameters with the application of uniaxial strain (±5%) is obtained in tetragonal BFO, in which the Rashba coefficient (αR) doubles with a compressive 5% strain, making tetragonal BFO a suitable candidate for spintronic applications. More importantly, full reversal of the in-plane spin texture is obtained for the opposite polarization states in tetragonal BFO with an activation energy barrier of 1.13 eV.

Non‐stoichiometric BZT‐BCT ferroelectrics with visible/near‐infrared photoresponse for broadband photodetection

AbstractThe bulk photovoltaic effect in ferroelectric materials exhibits great potential in photoelectric applications. However, their photoresponse is generally limited to the UV region due to the wide bandgap feature of most perovskite ferroelectric materials, while the narrowing of bandgap is often accompanied by the degradation or even extinction of the ferroelectric polarization. Herein, 0.5Ba(Zr0.2Ti0.8)O3‐0.5(Ba0.7Ca0.3)TiO3 (BZT‐BCT) with bandgap of 2.4 eV arising from the existence of Ti3+ is prepared, and then titanium vacancies are introduced to BZT‐BCT ferroelectric solid solutions through B‐site off‐stoichiometry (0.5Ba(Zr0.2Ti0.8)O3‐0.5(Ba0.7Ca0.3)Ti1 − x%O3, BZT‐BCT1 − x%) to further tune the bandgap. Lowest bandgap of 2.1 eV with near‐infrared (NIR) absorption is obtained for BZT‐BCT0.990 composition. Moreover, both the ferroelectricity and piezoelectricity (Pr = 14.3 μC/cm2, d33 = 415 pC/N) are well maintained after mitigating the effect of the increased oxygen vacancies associated with Ti‐deficiency on the spontaneous polarization by oxygen‐annealing treatment. More specifically, the oxygen‐annealing BZT‐BCT0.985 composition, showing at least 2.4‐fold photovoltage and 2.2‐fold photocurrent of the pristine BZT‐BCT ceramic, exhibits excellent transient pyroelectric current and stable photovoltaic current under xenon, NIR, and monochromatic visible lights. The photoelectric device based on the oxygen‐annealing BZT‐BCT0.985 ceramic performs wide‐spectrum photodetection properties from 405 nm light to NIR light, which makes it a potential candidate for self‐powered photodetector applications.

Fast Photostriction in Ferroelectrics.

Light-induced nonthermal strain, known as the photostrictive effect, offers a potential way to excite mechanical strain and acoustic wave remotely. The anisotropic photostrictive effect induced by the combination of bulk photovoltaic effect (BPVE) and converse piezoelectric effect in ferroelectric materials is known as too small and slow for the applications requiring a high strain rate, such as ultrasound generation and high-speed signal transmission. Here, a strategy to achieve high rate dynamic photostrictive strain by utilizing local fast responses under modulating continuous light excitation in the resonance condition is reported. A strain rate of 8.06 × 10-3 s-1 is demonstrated under continuous light excitation, which is at least one order of magnitude higher than previous studies on bulk samples as seen in the literature. The significant photostrictive response exists even in depoled ferroelectric material without overall polarization. The theoretical analyses show that fast ferroelectric photostriction can be obtained through the combinational interaction mechanism of local BPVE and local converse piezoelectric effect existing only in the microscopic scale, thus circumventing the slow and low efficient BPVE charging up process across the macroscopic electrical terminals. The achieved fast photostriction and new understandings will open new opportunities to realize future wireless signal transmission and light-acoustic devices.

Role of B-site disorder in the properties of lead-free Na0.5Bi0.5(Mg1/3Nb2/3)O3 ceramic: A possible electrocaloric material with low leakage current

The electrocaloric (EC) effect in ferroelectric materials has been studied extensively to develop materials for solid-state cooling applications. The Na0.5Bi0.5TiO3-based ferroelectric material is selected for this particular application. The Ti4+ of the lead-free Na0.5Bi0.5TiO3 is completely replaced by (Mg1/3Nb2/3)4+ to enhance the dielectric breakdown strength and to observe the EC effect. The lead-free Na0.5Bi0.5(Mg1/3Nb2/3)O3 is synthesized via the columbite route with optimized processing conditions. The material shows a frequency-independent high ferroelectric–paraelectric transition temperature (460 °C) with a slim polarization vs electric field loop. The adiabatic temperature change (ΔT) of the compound is evaluated from the temperature-dependent polarization behavior, and calculated ΔT is ≈ 0.135 K at room temperature. The room-temperature EC strength and leakage current of the material are examined to check its suitability for solid-state refrigeration.

Various facets of ferroelectrics as functional materials: an informative review

Nature has always amused us; sometimes it holds us in awe and sometimes it leaves us spellbound with its mysterious and inscrutable ways of working. The most significant and fundamental understanding of materials observed today is based on their constituent elements and position of the elements in the periodic table; which decides their property, behavior, reactivity and affinity with other elements. Given this primary aspects what comes secondary is the specificity or the multiplicity of functions that can be achieved from a material. In the present era, there is an incredible and massive increase in the number of functional materials to meet the ever-increasing need of electronic devices and their miniaturization. Functional materials have carved a special niche for itself in the field of material science. This review is exclusively intended to highlight and satiate the academic curiosity of novices about functional aspects of ferroelectric materials. It explores the various intricate and inherent principles and mechanisms which underpins the functional dimensions of ferroelectric materials. Ferroelectrics span a huge fraction of functional materials. Phenomenon like photovoltaic effect in ferroelectric materials, ferroelectric emission of electrons and their multifaceated applications are also discussed. Low dimensional ferroelectrics and their multifunctional prospects are also briefly covered in this review. It also includes brief idea of ferroelectric meta-materials, dielectric super-capacitors and its advantage over other preexisting ones. It is mostly informative and resourceful in providing multifunctional aspects of ferroelectrics. This review assures researchers who are genuinely interested in broadening their information base along with getting a fresh perspective into this emerging field of ferroelectrics as functional materials.

A phase-field simulation-based approach to determine flexoelectric coefficients from hysteresis loop of ferroelectrics

The flexoelectric effects in ferroelectric materials have attracted abundant attention in recent years due to the potential application in microscale mechanical-electrical devices. However, quantifying flexoelectric coefficients in ferroelectrics is still a challenge because of the complex electromechanical coupling in ferroelectric materials. Inspired by the flexoelectric effect-induced skew of the hysteresis curve, an indirect method is proposed in this article to determine the flexoelectric coefficient with reasonably high accuracy. Phase-field simulations show that such skew is stimulated only by the flexoelectric effect, which excludes the influence of other electromechanical coupling effects. In addition, the magnitude of such skew is in linear proportion to the flexoelectric coefficient. The four-point bending PbTiO3 beam model is calculated as an example to obtain the transversal flexoelectric coefficient of f1122.

Origin of Rashba Spin Splitting and Strain Tunability in Ferroelectric Bulk CsPbF3

Spin-orbit coupling (SOC) in conjunction with broken inversion symmetry acts as a key ingredient for several intriguing quantum phenomena, viz., Rashba-Dresselhaus (RD) effect. The coexistence of spontaneous polarization and the RD effect in ferroelectric (FE) materials enables the electrical control of spin degrees of freedom. Here, we explore the FE lead halide perovskite CsPbF3 as a potential candidate in the field of spintronics by employing state-of-the-art first-principles-based methodologies, viz., density functional theory (DFT) with semilocal and hybrid functional (HSE06) combined with SOC and many-body perturbation theory (G0W0). For a deeper understanding of the observed spin splitting, the spin textures are analyzed using the k.p model Hamiltonian. We find there is no out-of-plane spin component indicating that the Rashba splitting dominates over Dresselhaus splitting. We also observe that the strength of Rashba spin splitting can be substantially tuned on application of uniaxial strain (±5%). More interestingly, we notice reversible spin textures by switching the FE polarization in CsPbF3 perovskite, making it potent for perovskite-based spintronic applications.

Electrocaloric effect in ferroelectric materials: From phase field to first-principles based effective Hamiltonian modeling

Electrocaloric effect (ECE) of ferroelectrics has attracted considerable interest due to its potential application in environmentally friendly solid-state refrigeration. The discovery of giant ECE in ferroelectric thin films has greatly renewed the research activities and significantly stimulated experimental and theoretical investigations. In this review, the recent progress on the theoretical modeling of ECE in ferroelectric and antiferroelectric materials are introduced, which mainly focuses on the phase field modeling and first-principles based effective Hamiltonian method. We firstly provide the theoretical foundation and technique details for each method. Then a comprehensive review on the progress in the application of two methods and the strategies to tune the ECE are presented. Finally, we outline the practical procedure on the development of multi-scale computational method without experiemtal parameters for the screening of optimized electrocaloric materials.

Observation of negative capacitance in antiferroelectric PbZrO3 Films

Negative capacitance effect in ferroelectric materials provides a solution to the energy dissipation problem induced by Boltzmann distribution of electrons in conventional electronics. Here, we discover that besides ferroelectrics, the antiferroelectrics based on Landau switches also have intrinsic negative capacitance effect. We report both the static and transient negative capacitance effect in antiferroelectric PbZrO3 films and reveal its possible physical origin. The capacitance of the capacitor of the PbZrO3 and paraelectric heterostructure is demonstrated to be larger than that of the isolated paraelectric capacitor at room temperature, indicating the existence of the static negative capacitance. The opposite variation trends of the voltage and charge transients in a circuit of the PbZrO3 capacitor in series with an external resistor demonstrate the existence of transient negative capacitance effect. Strikingly, four negative capacitance effects are observed in the antiferroelectric system during one cycle scan of voltage pulses, different from the ferroelectric counterpart with two negative capacitance effects. The polarization vector mapping, electric field and free energy analysis reveal the rich local regions of negative capacitance effect with the negative dP/dE and (δ2G)⁄(δD2), producing stronger negative capacitance effect. The observation of negative capacitance effect in antiferroelectric films significantly extends the range of its potential application and reduces the power dissipation further.

Flexocaloric effect in ferroelectric materials: methods of indirect evaluation

Ferroelectric materials have great potential use for solid-state refrigeration. However, their working temperature is restricted to Curie temperature; the working temperature can be increased by the new component of strain gradient-driven caloric effect or flexocaloric effect (FCE). The FCE relies on the inhomogeneous strain of the crystal lattice to induce polarization in centrosymmetric crystals (flexoelectricity). The strain gradient-induced polarization is defined by flexoelectric polarization coefficient and is utilized to estimate the FCE. As the FCE is a relatively new phenomenon, several ways can be used to calculate it. Different methods of flexocaloric quantification in ferroelectric materials (Pb(Mg1/3Nb2/3)O3 and Ba0.67Sr0.33TiO3) are discussed in the present work. The FCE can be obtained based on the measured properties and combination between the polarization and strain. This allows one to study the actual or net flexocaloric behavior in the material. It was found that the quantification of temperature change varies according to the method used for estimation. The experimental confirmation is required for validation of the proposed methods of estimation. Further, this work also discusses the possibility of other ways that are untouched by the research community. The analysis indicates a substantial untapped potential for solid-state refrigeration and warrants further research.

Electrocaloric effect enhancement in compositionally graded ferroelectric thin films driven by a needle-to-vortex domain structure transition

Obtaining large electrocaloric (EC) effects in ferroelectric materials is a prerequisite for incorporating them into advanced solid-state cooling devices. Based on phase-field simulations, we propose an effective approach for improving the EC effect near room temperature in compositionally graded ferroelectric (CGFE) thin films (e.g., Pb1 − x Sr x TiO3) by controlling the compositional gradient along the direction of the thickness of the films. The simulation results reveal the formation of a stable needle-like domain structure in CGFE films with large composition gradients, while a periodic striped domain structure is found in small-composition-gradient CGFE films. The temperature dependence of polarization can be tailored by controlling the composition gradient in the films. With rising temperatures, a notable transition from a needle-like to a vortex domain structure is observed in CGFE films, which is distinguishable from that observed in homogeneous ferroelectric films. Our work demonstrates that the EC effect (the adiabatic temperature change, ΔT) can be greatly improved by the needle-to-vortex domain transition that occurs when the composition gradient is increased. When the composition gradient increases, a larger EC effect is achieved at lower temperatures. Large-composition-gradient films exhibit multiple peaks of ΔT. The local concentration of the total energy near the root of the needle domains is also found to drive the needle-to-vortex domain transition, giving rise to an enhancement of the EC effect in CGFE films. Our study provides a potential pathway for designing ferroelectric thin films with enhanced EC properties for energy-efficient solid-state refrigeration.