Defect Dipoles Research Articles

Defect Dipole Asymmetry Response Induces Electrobending Deformation in Thin Piezoceramics.

Ultrahigh electrostrains (>1%) in several piezoceramic systems have been reported since 2022, which attracts more and more interest in the field of piezoelectricity; however, the mechanism is still unclear. Here, in nonstoichiometric (K_{0.48}Na_{0.52})_{0.99}NbO_{2.995} ceramics, we have directly observed a novel electric field-induced bending (electrobending) phenomenon that visually exhibits an alternating concave-convex deformation under an electric field of ±50 kV cm^{-1}, leading to the measured ultrahigh electrostrain. It is demonstrated that the electrobending deformation arises from the different stresses due to the stretching or compression of the oriented-defect dipoles in the upper and lower surface layers of the ceramics under an electric field. Consequently, a giant apparent electrostrain of 31.8% is obtained at room temperature. Our discovery is an important addition and refinement to the field of condensed matter physics, while also providing a new strategy and shedding light on the design of future high-performance actuators and intelligent devices.

Enhanced energy storage performance of 0.85BaTiO3–0.15Bi(Mg0.5Hf0.5)O3 films via synergistic effect of defect dipole and oxygen vacancy engineering

Dielectric capacitors are widely used in electronic devices due to their ultra-fast charge/discharge rate and ultra-high power density, but their lower energy density and poor thermal stability limit their further application. In contrast to the traditional strategy of suppressing defects, this work combines oxygen vacancies with defect dipoles to improve the breakdown strength and polarization behavior of ferroelectric films. Low concentration of oxygen vacancies and defect dipoles can trap charge carriers and increase breakdown strength, but if the concentration is too high, it can easily make films prone to breakdown. Moreover, the defect dipoles can reduce Pr by providing intrinsic restoring force for polarization switching, while excessive defect dipoles and oxygen vacancies can pin domain walls and increase Pr. By delicately controlling the concentration of oxygen vacancies and defect dipoles in the film, the BT-BMH film deposited at 0.135 mbar achieved the maximum breakdown strength and slim P-E loops, inducing the energy density to reach 108.9 J·cm-3 with an efficiency of 79.6 % at room temperature and excellent thermal stability in the wide temperature range of -100∼350 °C with the energy density of 69.1 J·cm-3. This work reveals the important significance of reasonable defect control for improving energy storage performance and provides an effective method for developing high-performance dielectric capacitors.

Linear dielectric ceramics for near-zero loss high-capacitance energy storage

High energy-density (Wrec) dielectric capacitors have gained a focal point in the field of power electronic systems. In this study, high energy storage density materials with near-zero loss were obtained by constructing different types of defect dipoles in linear dielectric ceramics. Mg2+and Nb5+ are strategically chosen as acceptor/donor ions, effectively replacing Ti4+ within Ca0.5Sr0.5TiO3-based ceramics. The results indicate that under an applied electric field, specific defects such as [MgTi″−VO··] and [NbTi·−Ti3+], can effectively regulate VO·· and electron movement, significantly reducing losses. Furthermore, high-density insulating grain boundaries, reduced VO·· concentrations and diminished carrier mobility contribute to enhanced resistivity, resulting in high Wrec ∼7.62 J/cm3 and η ∼92 % at 640 kV/cm, making it one of the most promising linear dielectrics to date. Notably, Wrec and η remain remarkably stable across a broad range of frequencies (1–500 Hz), temperatures (25–175 °C) and numerous cycles (up to 106). Additionally, finite element software was used to simulate the distribution of dielectric constant, electric potential, and local electric field, further verifying the correlation between microstructure and breakdown resistance. This innovative work provides a sustainable strategy to optimize the energy storage capacity of lead-free ceramics over a wide temperature range through strategic manipulation of defects.

Oxygen vacancy induced defect dipoles in BiVO4 for photoelectrocatalytic partial oxidation of methane

A strong driving force for charge separation and transfer in semiconductors is essential for designing effective photoelectrodes for solar energy conversion. While defect engineering and polarization alignment can enhance this process, their potential interference within a photoelectrode remains unclear. Here we show that oxygen vacancies in bismuth vanadate (BiVO4) can create defect dipoles due to a disruption of symmetry. The modified photoelectrodes exhibit a strong correlation between charge separation and transfer capability and external electrical poling, which is not seen in unmodified samples. Applying poling at −150 Volt boosts charge separation and transfer efficiency to over 90%. A photocurrent density of 6.3 mA cm−2 is achieved on the photoelectrode after loading with a nickel-iron oxide-based cocatalyst. Furthermore, using generated holes for methane partial oxidation can produce methanol with a Faradaic efficiency of approximately 6%. These findings provide valuable insights into the photoelectrocatalytic conversion of greenhouse gases into valuable chemical products.

High Temperature-Insensitive Electrostrain Obtained in (K, Na)NbO3-Based Lead-Free Piezoceramics.

Over the last decades, notable progress is achieved in (K, Na)NbO3 (KNN)-based lead-free piezoceramics. However, more studies are conducted to increase its piezoelectric charge coefficient (d33). For actuator applications, piezoceramics need high electric-field induced strain under low electric fields while maintaining exceptional temperature stability across a wide temperature range. In this study, this work developes Li/Sb-codoped KNN (LKNNS) ceramics with high electrostrain by defect engineering and domain engineering. A remarkable strain of 0.43%, along with a giant d33* value of 2177 pm V-1, is attained in the LKNNS ceramic at 20 kV cm-1. The ceramic exhibits a minimal performance decrease of less than 15% over a temperature range from room temperature to 150 °C. The exceptional strain is attributed to the presence of A-site vacancy-oxygen vacancy ( ) defect dipoles and the increase in nano-domains. The hierarchical domain configuration and defect dipoles impede the switched domains from reverting to their original state as temperature increases, furthermore, the elongated dipole moments of caused by rising temperatures compensate for strain reduction results in exceptional temperature stability. This study provides a model for designing piezoelectric materials with exceptional overall performance under low electric fields and across a wide temperature range.

Giant permittivity and humidity sensitivity of SrTiO3 based ceramics induced by K, Nb donor-acceptor co-doping

This research utilizes a solid-state sintering process to fabricate a series of Sr1-xKxTi1-xNbxO3 (x =0.01, 0.02, 0.025, 0.03) ceramics. The sample with a doping concentration of x=0.025 achieved a dielectric constant of 10409 and a dielectric loss of 0.026 at 1 kHz. With increased dopant concentrations of K and Nb, the thermal stability of the ceramics is significantly enhanced, as evidenced by a dielectric constant variation of less than 15 % for x=0.025 sample over a temperature range from room temperature to 240 °C. Employing activation energy analysis, impedance spectroscopy, humidity response assessments, and X-ray photoelectron spectroscopy, it is indicated that the excellent electrical performance is attributed to the combined effects of the Internal Barrier Layer Capacitance and the formation of complex defect dipoles. Moreover, the insights into the moisture characteristics of SrTiO3 presented in this paper imply that the giant dielectric Sr1-xKxTi1-xNbxO3 ceramics have potential in the application of humidity sensing devices.

Deuteration removes quantum dipolar defects from KDP crystals

Dielectric properties of the hydrogen-bonded ferroelectric crystal KH2PO4 (KDP) differ significantly from those of KD2PO4 (DKDP). It is well established that deuteration affects the interplay of hydrogen-bond switches and heavy ion displacements that underlie the emergence of macroscopic polarization, but a detailed microscopic model is missing. We show that all-atom path integral molecular dynamics simulations can predict the isotope effects, revealing the microscopic mechanism that differentiates KDP and DKDP. Proton tunneling generates phosphate configurations that do not contribute to the polarization. At low temperatures, these quantum dipolar defects are substantial in KDP but negligible in DKDP. These intrinsic defects explain why KDP has lower spontaneous polarization and transition entropy than DKDP. The prominent role of quantum fluctuations in KDP is related to the unusual strength of the hydrogen bonds and should be equally important in other crystals of the KDP family, which exhibit similar isotope effects.

Role of ZnO dopant in enhancing piezoelectric characteristics in KNN‐based piezoelectric ceramics

AbstractConsidering that lead‐based piezoelectric ceramics are not conducive to sustainable development, the research and preparation of environmentally friendly lead‐free piezoelectric ceramics has become a new trend. Among them, potassium‐sodium niobate based (KNN‐based) piezoelectric ceramics are considered as the most potential candidates because of their good piezoelectric properties. However, the strong sensitivity to temperature has hindered the further application of KNN‐based ceramics. In this work, the ZnO dopant was introduced in 0.96K0.48Na0.52Nb0.96Sb0.04O3–0.04Bi0.5Na0.5HfO3 ceramics to improve their piezoelectric characteristics. On the one hand, Zn2+ could occupy B‐site and thus enhance the lattice distortion of BO6 octahedra, resulting the enhanced piezoelectric properties including kp = 46%, d33 = 344 pC/N and TC = 282°C in the optimal component with x = 0.01. On the other hand, the defect dipole formed by the acceptor dopant Zn2+ pinned the motion of domain wall, and thus improved the temperature stability over a wide temperature range of 20°C to 180°C, where the descent in unipolar strain decreased from 35% (x = 0) to 23% (x = 0.01). This work provides a point of view about how ZnO dopants make an influence on the KNN‐based ceramics.

Enhanced magnetoelectric response in Sc-doped BiFeO3-BaTiO3 Ceramics

In recent years, the single-phase BiFeO3-BaTiO3 multiferroic ceramics have gained attention for their magnetoelectric response above room temperature, but substantial endeavors to improve the property have yielded modest results. An optimized BiFe(1-x)ScxO3-BaTiO3 composition having magnetoelectric coefficient (αME) ∼ 567 mV/(cm·Oe)) measured at the resonant frequency (∼95 kHz) is reported in this work. The high αME is attributed to the combined effect of improved piezoelectric coefficient and enhanced ferromagnetism. Improved piezoelectricity is attributed to enhanced intrinsic response caused by the octahedral distortions, and enhanced ferromagnetism is induced by the destabilized cycloidal spin structure resulting from the octahedral distortions. Besides, the addition of Sc3+ can exhibit increased resistivity and reduced defect dipole effects, which is conducive to improving electric properties.

High energy storage performance in Mg modified BaTiO3 films with superparaelectric behavior

In this work, by doping the B-site of BaTiO3 with Mg elements, we have prepared BaMgxTi1-xO3-x(BMxT) films with superparaelectric behaviors. The microstructures, polarization behaviors, breakdown strength, leakage current density, and energy storage performance are investigated systematically of the BMxT films. The breakdown strength of the film reaches 7.5MV/cm when x = 0.18, at the same time, excellent energy storage density (67.7J/cm3) and energy storage efficiency (94.9%) are obtained, which is attributed to the doping of the acceptor element Mg. By doping Mg with a lower chemical valence state to form defect dipoles in the lattice, the breakdown strength and polarization properties of the film are improved while reducing the crystallinity of the film, forming a hysteresis loop with superparaelectric properties. This work provides a feasible route to design superparaelectric materials with simple compositions for high-performance capacitive energy-storage.

Structure regulation and performance optimization mechanism of Sr0.7Bi0.2TiO3-based energy storage ceramics based on charged defect design engineering

The linear-like relaxor ferroelectric Sr0.7Bi0.2TiO3 with regulable microstructure offers a new platform to reveal the essential mechanism of energy storage properties improvement and develop advanced pulse capacitors. Herein, Li with relatively weak volatility accompanied by Bi was introduced in Sr0.7Bi0.2TiO3 to form a charged defect and increase the maximum polarization (Pmax) while avoiding the deterioration of dielectric breakdown strength (BDS). The occupation of Li and the formation of Li-Bi defect dipole polar were analyzed using first principle calculations. A unique local superlattice induced by the lattice distortion was first observed in related systems. The Pmax was enhanced due to the increased size and number of polar structures. The breakdown behaviour and local electric field distribution were analyzed using numerical simulation. The BDS was improved due to the decreased oxygen vacancies, high thermal conductivity and enhanced electrical insulation. The excellent and stable energy storage performance was achieved in different temperatures, frequencies and cycles. Meanwhile, the optimized sample possesses excellent and stable charge–discharge properties, especially fatigue resistance (105 cycles under 25 °C and 150 °C). After the process optimization, the sample shows a higher energy storage density of 3.44 J/cm3 with a high efficiency of 93.74 % at 345 kV/cm due to the further enhanced BDS. In this work, the performance improvement mechanism was studied in-depth, providing a new strategy for optimizing linear-like lead-free relaxor ferroelectric energy storage properties.

Enhancement of the Piezocatalytic Response of La-Doped BiFeO3 Nanoparticles by Defects Synergy.

Because of their intrinsic polarization and related properties, ferroelectrics attract significant attention to address energy transformation and environmental protection. Here, by using trivalent-ion-lanthanum doping of BiFeO3 nanoparticles (NPs), it is shown that defects and piezoelectric potential are synergized to achieve a high piezocatalytic effect for decomposing the model Rhodamine B (RhB) pollutant, reaching a record-high piezocatalytic rate of 21360 L mol-1 min-1 (i.e., 100% RhB degradation within 20min) that exceeds most state-of-the art ferroelectrics. The piezocatalytic Bi0.99La0.01FeO3 NPs are also demonstrated to be versatile toward various pharmaceutical pollutants with over 90% removal efficiency, making them extremely efficient piezocatalysts for water purification. It is also shown that 1% La-doping introduces oxygen vacancies and Fe2+ defects. It is thus suggested that oxygen vacancies act as both active sites and charge providers, permitting more surface adsorption sites for the piezocatalysis process, and additional charges and better energy transfer between the NPs and surrounding molecules. Furthermore, the oxygen vacancies are proposed to couple to Fe2+ to form defect dipoles, which in turn introduces an internal field, resulting in more efficient charge de-trapping and separation when added to the piezopotential. This synergistic mechanism is believed to provide a new perspective for designing future piezocatalysts with high performance.

Deciphering the Effect of Defect Dipoles on the Polarization and Electrostrain Behavior in Perovskite Ferroelectrics.

Defect dipoles are crucial for regulating electromechanical properties in piezoelectric ceramics, but their effects on polarization and electrostrain behaviors are still unclear. Here, a reasonable theoretical model is proposed and evidenced by experiments to address a long-standing puzzle of the relationship between the internal bias field and defect dipoles. By incorporating the additional polarization induced by defect dipoles, we refine the classical theory to account for the recently reported asymmetric giant-strain behaviors. Phase-field simulation reveals the electrostrain evolution in response to defect dipole elastic distortion and additional polarization. This work not only elucidates the effect of defect dipoles on polarization and electrostrain but also advances the theoretical understanding of defects in piezoelectrics.

Piezoelectric Ceramic Hardening Through Defect Distribution Optimization in Multicomponent Systems

AbstractAcceptor doping is a common method for hardening modified piezoelectric ceramics. The mechanism through which the hardening effect can be improved has been widely studied and verified. However, the effect of defects caused by different valence states of the B‐site ions on the properties of multicomponent piezoelectric ceramics remains to be discussed. Therefore, in this work, a novel Pb(Ni1/3Nb2/3)O3–Pb(In1/2Nb1/2)O3–Pb(Mn1/3Nb1/2)–PbTiO3 quaternary hard ceramic with excellent performance is prepared and studied. The interaction between grain‐boundary defects and defect dipoles is proposed to be the mechanism behind the observed excellent performance. It is found that different types of defects improve the hardening effect in various ways. These results can provide a theoretical basis for the preparation of multicomponent piezoelectric ceramics with better properties.

Ultra-high energy storage characteristics under low electric field in Sm-doped Bi5Mg0.5Ti3.5O15 films through defect dipole engineering

The sol–gel method was used to fabricate lead-free Bi5-xSmxMg0.5Ti3.5O15 (BSxMTO, x = 0.25) relaxor ferroelectric film, which exhibited a recoverable energy storage density of 64 J/cm3 and an energy efficiency of 81.1 % under 1856 kV/cm. The energy storage response specifically reaches as high as 0.1824 J/kV·cm2. Enhancing the ergodic relaxor characteristics, improving the defect dipole driving, and reducing defect concentration are essential factors for BSxMTO (x = 0.25) film to collaboratively achieve enhanced relaxor characteristics and polarization intensity, thereby resulting in excellent medium- and low-field energy storage performances. Furthermore, the BSxMTO (x = 0.25) film also exhibits excellent stability in frequency (1 kHz − 20 kHz) (Ure ∼ (40.95 ± 1.01) J/cm3, η ∼ 85.7 % ± 4.4 %) and temperature (20 °C − 150 °C) (Ure ∼ (40.87 ± 0.30) J/cm3, η ∼ 80.4 % ± 2.2 %) under 1387 kV/cm, offering promising prospects for the application of lead-free dielectric energy storage films in low and medium electric fields.

A high-power piezoelectric ceramic with great electrical properties and temperature stability

Lead-based Pb(Zr, Ti)O3 ceramics have been widely used in high-power piezoelectric applications, but its stable operation at high temperature is still a grand challenge. In this work, the third element Pb(Mn1/3Sb2/3)O3 (PMS) was incorporated into Pb(Zr0.48Ti0.52)O3 (PZT) to design the xPb(Mn1/3Sb2/3)O3-(1-x)Pb(Zr0.48Ti0.52)O3 (PMS-PZT) ternary ceramics through the phase diagram. The ceramics with morphotropic phase boundary (MPB) structure and uniform grain size were fabricated successfully. The dielectric, ferroelectric and piezoelectric properties of the ceramics were probed respectively. Excellent piezoelectric properties (Qm=1595, kp=0.61, d33=318pC/N, tanδ=0.60 %, Tc=300℃) were obtained in 0.075PMS-0.925PZT ceramic, which can be attributed to its MPB structure and the pinning effect of defect dipoles on domain rotation. Moreover, the T-phase dominated 0.075PMS-0.925PZT ceramic obtains great temperature stability with a low variation of resonant frequency below 2.2 % and no variation of non-resonant frequency in the temperature range from 25°C to 175°C. These results make the ceramic as a good candidate for piezoelectric frequency applications that require constant performance within a wide temperature range.

Superior energy storage performance in lead-free SrTiO3 films via ion doping and crystalline optimization

SrTiO3 paraelectric materials exhibit significant potential to be used as lead-free energy storage dielectrics due to their distinctive linear-like polarization behavior. Nonetheless, the application in advanced thin-film capacitors is challenging due to their low polarization strength and structural anomalies, which reduce the breakdown field strength and diminish the energy storage density. This study proposes a synergistic approach that integrates ion doping with the optimization of thermal treatment to enhance the energy storage capabilities of SrTiO3 thin films. Initially, Mn2+ doping in SrTiO3 films mitigates oxygen vacancies and forms Mn2+-VO•• defect dipoles, thereby refining the polarization behavior and reducing the leakage current density. Subsequently, the crystalline degree of SrTi0.99Mn0.01O3 thin films can be regulated by adjusting the annealing temperature. The optimal breakdown field strength of the resultant SrTi0.99Mn0.01O3 films reaches 4681 kV/cm with a 1 mol% Mn2+ doping level, enhancing the recoverable energy storage density (Wrec) to 32.17 J/cm3. Furthermore, the recoverable energy storage density of SrTi0.99Mn0.01O3 films escalates to 36.62 J/cm3 with an efficiency of 80.28 %, upon reducing the annealing temperature to 625 °C. Moreover, SrTi0.99Mn0.01O3 films demonstrate superior thermal stability, frequency stability, and electrical fatigue resistance, underscoring their potential as efficacious materials for film capacitor applications.

The phase composition, dielectric, and energy storage performance of A-site vacancy modulated BaTiO3 ceramics with Bi(In1/2(Li0.5Ta0.5)1/2)O3 modification

The (1-x)Ba0.94Ce0.04TiO3-xBi(In1/2(Li0.5Ta0.5)1/2)O3 (BCT-BILT) relaxor ferroelectric ceramic system was explored based on the A-site vacancy design and defect dipole engineering. The impacts of different doping concentrations on the phase composition, dielectric and energy storage performance of the BCT-BILT ceramics were studied and discussed in detail. The pure BCT and 0.95BCT-0.05BILT samples exhibited a mixed crystal structure of tetragonal (T) and pseudo-cubic (PC) phase, while the BCT-BILT samples with x > 0.05 possessed a cubic (C) phase, accompanied by the secondary phases of BaBi2Ta2O9 and BaTa2O6. With an increase in the BILT doping concentration, the surface morphologies of the ceramics were continuously modulated, and the dielectric loss had been reduced to 0.001 at 1 kHz, which was beneficial to improve the energy storage properties. Compared to the pure BCT, the breakdown field strength was significantly enhanced owing to the formation of Aurivillius phase BaBi2Ta2O9 and the increased dielectric relaxation. Ultimately, the highest energy storage density of Wrec = 0.7 J/cm3 and high energy conversion efficiency of η = 95 % was realized at the composition of x = 0.05 under a small electric field of 130 kV/cm. Furthermore, the good temperature stability with the ΔWrec/Wrec30°C < 9 % and Δη/η30°C < 6.5 % was acquired for the samples with x = 0.20–0.30 in the temperature range of 30–120 °C, owing to the synergistic roles of the defect dipoles, impurities BaBi2Ta2O9, and polar nanoregions (PNRs). The 0.95BCT-0.05BILT ceramic obtains discharge energy density Wdis of 0.35 J/cm3 and fast discharge speed t0.9 of 312 ns at 60 kV/cm, current density CD of 255.4 A/cm2 and power density PD of 10.2 MW/cm3 at 80 kV/cm. This work is of guiding significance for designing and optimizing energy storage performance of lead-free relaxors from the perspective of defect building and engineering.

Strong pinning effect on domains in piezoelectrics

In high-power applications, since mechanical losses in piezoelectric devices always result in considerable heat generation, the temperature stability of the mechanical quality factor (Qm) is particularly crucial and should be considered in real piezoelectric applications. Here, we propose a poling-aging-repoling strategy to make the defect dipoles aligned with the poling direction as much as possible, thereby resulting in the strong pinning of ferroelectric domains. A giant internal bias field Ei (11.6 kV cm−1 @ 1 Hz) and a high Qm (2074), accompanied by almost unchanged d33, are obtained in the composition of CuO-doped (K0.48Na0.52)0.94Li0.06Nb0.94Ta0.06O3 (KNNLT-Cu) ceramics with a diffused polymorphic phase transition. Furthermore, and this is more encouraging, the high electromechanical performance exhibits good temperature stability in the range from room temperature to 100 °C, suggesting that the thermal stability of Qm can be effectively improved by combining the strong pinning of defect dipoles with composition design and providing a way for the development and design of future high-power piezoelectric devices.

Local defect structure design enhanced energy storage performance in lead-free antiferroelectric ceramics

Antiferroelectrics (AFEs) are ideal candidates in dielectric, electromechanical, and electrothermal applications. NaNbO3 (NN), as a lead-free antiferroelectric (AFE) material under extensive investigation, exhibits ferroelectric (FE)-like polarization–electric field (P-E) hysteresis loops, characterized by high remnant polarization and large hysteresis. Herein, the local defect structure design is proposed to achieve high energy storage (ES) density in NN-based AFE ceramics. The pinning effect of defect dipoles and the enhancement of local structural disorder stabilize the AFE phase and reduce hysteresis losses. Consequently, an excellent ES performance of large recoverable energy density (Wrec) of 9.70 J/cm3 and high efficiency (η) of 88.75 % is concurrently obtained in NN-based relaxor AFE ceramics, with outstanding charge–discharge performance (PD∼413.2 MW/cm3, WD∼4.47 J/cm3), which are significantly improved compared to other reported values in lead-free ES ceramics. This indicates that NN-based ceramics are candidates for advanced ES capacitors and provides a feasible modulation approach for the development of new lead-free high-performance dielectric materials.