Lead-free Piezoelectric Ceramics Research Articles

Advancing energy storage capabilities in 0.7BNST(1-x)-0.3BLMNx lead-free dielectric ceramic materials

Lead-free ferroelectric ceramics with a composition of 0.7(Bi0.5Na0.5)0.7Sr0.3Ti(1-x)O3-0.3Ba0.94La0.04(Mg1/3Nb2/3)xO3 (abbreviated as 0.7BNST(1-x)-0.3BL(MN)x, 0 ≤ x ≤ 0.12) were prepared using solid-phase sintering method, involving co-substituting at A and B sites. High recoverable energy density (Wrec) of 3.54 J/cm3 and energy efficiency (η) 85.49% are achieved at an electric field of 270 kV/cm. Furthermore, these ceramics exhibited excellent temperature and cycle stability at 120 kV/cm (within 25 °C–150 °C, Wrec fluctuation range <14 %; under 1∼106 cycles, the Wrec fluctuation range <5 %). In terms of dielectric performance, they exhibited a high dielectric constant (εr∼4540), an extremely low dielectric loss tanδ of <0.04 (30 °C–300 °C), and good temperature stability with Δε/ε150 °C ≤ ±15 % (−19.5 °C–233.4 °C). During the charging and discharging process, these ceramics demonstrated a high energy density (Wd) of 1.2 J/cm3, a power density (PD) of 61.7 MW/cm3, and an extremely short discharge time (t0.9) of approximately ∼0.11 μs＀ This study has improved the dielectric energy storage performance of BNT-based lead-free piezoelectric ceramics, making them suitable for use in pulse power devices.

Study on physical, electrical, magnetic and energy harvesting performances of eco-friendly piezoelectric ceramics (1 − x)[0.995BNKT–0.005LN]–xFe2O3 complex system

ABSTRACT In this work, the complex lead-free piezoelectric ceramics with formula (1 − x)[0.995 Bi0.5(Na0.80K0.20)0.5TiO3–0.005LiNbO3]–xFe2O3, where x = 0, 0.010, 0.015 and 0.020 mol fraction, have been prepared via a conventional solid-state method. The effects of Fe2O3 doping on the physical, microstructural electrical, energy harvesting and magnetic properties have been systematically investigated. All ceramics were sintered at 1150°C for 2 hours with obtained relative density of ~ 96-97%. The XRD and Raman data revealed the coexisting rhombohedral and tetragonal phases for all samples. SEM image presented angular grain packing with the average grain size range of 0.43–1.03 μm. The addition of Fe2O3 content improved in electrical properties of undoped sample particularly at a composition of x = 0.015. The maximum values of ε m = 6250, S max = 0.29, d*33 = 578 pm/V, d 33 = 211 pC/N and FOM = 3.54. All ceramics indicated ferromagnetic behavior with slim hysteresis shape. The results suggest a potential for its applications as an eco-friendly compound for further use in sensor, spintronic and microelectronic devices applications.

Boosting Low-E electro-strain via high-electronegativity B-site substitution in lead-free K0.5Na0.5NbO3-based ceramics

Lead-free piezoelectric actuators emerge as promising substitutes for their lead-containing counterparts to address environmental concerns. However, they often confront a trade-off between low driving electric fields and high electro-strain. Herein, a novel strategy to boost electro-strain under low electric fields is proposed by doping high-electronegativity B-site atoms into perovskite potassium sodium niobate-based ceramics. Our findings reveal that high-electronegativity B-site atoms elevate the covalency of B-O bonding, softening the short-range repulsion and introducing local multiphase coexistence. This leads to more nanoscale domain structures and lower coercive field, thereby enabling large strains to be produced at lower electric fields. Notably, a substantial 0.2 % bipolar electro-strain and 0.1 % unipolar electro-strain under 10 kV cm-1 is achieved in Sr, Sb co-doped potassium sodium niobate ceramics, with a broad working frequency and temperature range, as well as excellent fatigue resistance. This study unveils innovative insights into designing lead-free piezoelectric ceramics with remarkable electro-strain performance and low driving electric field, promising a significant advancement in lead-free piezoelectric materials science and piezoelectric actuators.

Synergistic enhancement of electrical characteristics in Sr2+ and Zr4+ Co-doped BaTiO3 ceramics through multiphase coexistence regulation at room temperature

BaTiO3 (BT)-based ceramics have recently become one of the most promising lead-free piezoelectric ceramics. However, its overall performance still falls short of meeting the demands for multifunctional applications. Although phase boundary regulation can enhance the piezoelectric properties, BT ceramics have very separate phase transition temperatures for different phases. This leads to the difficulty of achieving multiphase coexistence at room temperature (RT). In this work, based on doping 0.08 mol Zr4+, the lead-free Ba1-xSrxTi0.92Zr0.08O3 [x = 0, 0.04, 0.08, 0.12, 0.16, 0.20 (mol), B1-xSxTZ] piezoelectric ceramics were prepared using the solid-state reaction method, and the effect of the Sr2+ doping level on the multiphase structural evolution and piezoelectric properties was systematically investigated. The results demonstrated that with the increase in the Sr2+ doping content, multiphase coexistence within the B1-xSxTZ ceramics was successfully achieved at RT. Moreover, it showed significant synergistic improvements in piezoelectric, dielectric, and electric-field-induced strain properties. At the doping level of about x = 0.16 mol, the key performance metrics of the piezoelectric ceramics were optimal. The d33 at room temperature reached ∼447 pC/N, kp ∼0.49, and εr ∼4649. Under an applied electric field of 10 kV/cm, Spos was ∼0.092 %, and d33∗ was ∼895 p.m./V. Therefore, this study provides new insights into the progress of advanced lead-free piezoelectric materials for multifunctional applications.

High Piezoelectric Performance of KNN-Based Ceramics over a Broad Temperature Range through Crystal Orientation and Multilayer Engineering.

Uninterrupted breakthroughs in the room temperature piezoelectric properties of KNN-based piezoceramics have been witnessed over the past two decades; however, poor temperature stability presents a major challenge for KNN-based piezoelectric ceramics in their effort to replace their lead-based counterparts. Herein, to enhance temperature stability in KNN-based ceramics while preserving the high piezoelectric response, multilayer composite ceramics were fabricated using textured thick films with distinct polymorphic phase transition temperatures. The results demonstrated that the composite ceramics exhibited both outstanding piezoelectric performance (d33~467 ± 16 pC/N; S~0.17% at 40 kV/cm) and excellent temperature stability with d33 and strain variations of 9.1% and 2.9%, respectively, over a broad temperature range of 25-180 °C. This superior piezoelectric temperature stability is attributed to the inter-inhibitive piezoelectric fluctuations between the component layers, the diffused phase transition, and the stable phase structure with a rising temperature, as well as the permanent contribution of crystal orientation to piezoelectric performance over the studied temperature range. This novel strategy, which addresses the piezoelectric and strain temperature sensitivity while maintaining high performance, is well-positioned to advance the commercial application of KNN-based lead-free piezoelectric ceramics.

Enhanced in-situ piezoelectric properties and thermal stability of lead-free BiFeO3-BaTiO3 ceramics by local structural heterogeneity

In perovskite-structure Bi-based piezoelectric ceramics, an increase in the actual operating temperature is usually accompanied by a sharp deterioration of the piezoelectric constant (d33), an unresolved paradox that severely limits their practical applications. In this paper, 0.67BF-0.33BT-0.02BZT-xBA lead-free piezoelectric ceramics designed using a synergistic strategy are presented. High Tdr and large d33 compatibility is achieved by regulating the ratio of polar phases in multiphase coexistence, grain size and domain structure. X = 0.01 ceramics have an in-situ d33 ranging up to 801 pC/N, Tdr = 361 °C, and Tc = 432 °C. The results of this study provide a novel design idea for the preparation of high-performance BF-BT lead-free piezoelectric ceramics.

Evolution of microscopic domain structure and macroscopic properties of (1-x)(Bi0.5Na0.5)TiO3-xBaTiO3 ceramic coatings

Sodium bismuth titanate-based ferroelectric materials have a promising application in modern microdevices due to their strong ferroelectricity and high Curie temperature. The domain structure plays a crucial role in the piezoelectric and ferroelectric properties of (1-x)(Bi0.5Na0.5)TiO3-xBaTiO3 ((1-x)BNT-xBT)(x=0, 0.06, 0.08, 0.10) ceramic coatings. In this paper, (1-x)BNT-xBT ceramic coatings were prepared by supersonic plasma spraying. Piezoresponse-force microscopy (PFM) was employed to gain insight into the microscopic domain evolution of (1-x)BNT-xBT ceramic coatings. Piezoelectric-force Microscopy (PFM) results show that the 0.92BNT-0.08BT ceramic coating exhibits relatively homogeneous striped domains and island domains, as well as a maximum amplitude response with an average amplitude intensity of 67.6 pm, which increases the localized piezoelectric response of the ceramic coating. The switching spectroscopy piezoelectric-force microscopy (SS-PFM) results show that the local piezoelectric coefficient (PRmax) of the 0.92BNT-0.08BT ceramic coating reaches 426.5 pm/V at 15 V, and the ferroelectric domains exhibit significant switching behavior. This study provides new ideas to further understand the relationship between microscopic electrical domains and macroscopic properties of these important lead-free piezoelectric ceramics.

Effects of electrical and mechanical properties of Ba0.92Ca0.08Zr0.05Ti0.95O3 ceramics with lanthanum dopants

Element doping is one of the important approaches to improve the performance of lead-free piezoelectric ceramics. In this study, Ba0·92Ca0·08Zr0·05Ti0·95O3-xLa (BCZT-xLa) piezoelectric ceramics were prepared by sol–gel method. The effects of La3+ contents on the phase structure, mechanical properties, and electrical properties of BCZT-xLa ceramics were investigated. Results showed that La3+ could affect the properties of ceramics by adjusting the concentration of oxygen vacancies and microstructure. When the La3+ contents were 0.008, the ceramics showed the best performance (the maximum permittivity was 8736.27, the remnant polarisation was 9.69 μC/cm2 and the coercive field was 3.44 kV/cm). The influences of Vickers hardness on ceramics were investigated using various La3+ contents. The lattice energy and oxygen vacancies were the main factors for the change in Vickers hardness. With an increment of x, the Vickers hardness values decreased from 6.271 GPa to 1.438 GPa. This study could provide a reference for BCZT piezoelectric ceramics doped with rare earth elements.

Preparation of K0.48Na0.52NbO3 & akermanite composite ceramics with biodegradability for cancellous bone repair by digital light processing

Lead-free piezoelectric ceramics can generate electrical signals to promote bone defect repair, but they suffer from low bioreactivity. In this study, K0.48Na0.52NbO3 & akermanite composite ceramic (KNN & AK) was prepared using digital light processing (DLP). The influence of sintering temperature and AK content was investigated. With the increase of sintering temperature, the piezoelectric coefficient d33 of the composite ceramics first increased and then decreased, reaching a maximum of 7.80 pC/N at 1070 °C. The doping of AK would lead to a significant decrease in the piezoelectric property, and the AK content should not exceed 10 wt% to achieve the piezoelectric coefficient of human bone. After immersion in Tris-HCl solution for 28 days, the weight loss rate of the composite ceramics doped with 15 wt% AK could reach 8.36 %. The combination of KNN and AK promotes the application of piezoelectric bone scaffolds in the field of bone repair.

Enhanced buoyancy and propulsion in 3D printed swimming micro-robots based on a hydrophobic nano-fibrillated cellulose aerogel and porous lead-free piezoelectric ceramics

This paper provides the first demonstration of additively manufactured swimming micro-robots which combine a hydrophobic nanofibrillated cellulose aerogel, to provide long-term buoyancy, with a low acoustic impedance porous piezoelectric ceramic for improved propulsion. The hydrophobic nanocellulose aerogel is shown to exhibit a high and stable contact angle that was maintained for extended periods of time, which facilitates long-term and stable buoyancy of the micro-robot. To quantify the benefits of introducing porosity into the active piezoelectric element, a new analysis model was developed to inform material design and maximize the acoustic propulsion force. Detailed characterisation and modelling of the swimming robots demonstrated that a swimming robot based on a lead-free porous Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) ceramic exhibited a higher acoustic radiation propulsion force and a faster swimming speed compared to a robot fabricated using a dense ceramic element. These benefits were associated with the lower elastic modulus, density and acoustic impedance of the porous piezoelectric material. The lower dielectric constant, reduced device capacitance, and lower resonant frequency of the porous piezoelectric element also significantly reduced the driving current and power requirements of the robot. This work therefore provides new insights on the impact of hydrophobic and acoustically matched piezoelectric materials on the performance of swimming micro-robots, and successfully demonstrates the use of porosity to improve acoustic impedance matching of resonant piezoelectric devices, such as micro-robots and ultrasonic transducers.

Preparation and Properties of Nb5+-Doped BCZT-Based Ceramic Thick Films by Scraping Process.

A bottleneck characterized by high strain and low hysteresis has constantly existed in the design process of piezoelectric actuators. In order to solve the problem that actuator materials cannot simultaneously exhibit large strain and low hysteresis under relatively high electric fields, Nb5+-doped 0.975(Ba0.85Ca0.15)[(Zr0.1Ti0.9)0.999Nb0.001]O3-0.025(Bi0.5Na0.5)ZrO3 (BCZTNb0.001-0.025BiNZ) ceramic thick films were prepared by a film scraping process combined with a solid-state twin crystal method, and the influence of sintering temperature was studied systematically. All BCZTNb0.001-0.025BiNZ ceramic thick films sintered at different sintering temperatures have a pure perovskite structure with multiphase coexistence, dense microstructure and typical dielectric relaxation behavior. The conduction mechanism of all samples at high temperatures is dominated by oxygen vacancies confirmed by linear fitting using the Arrhenius law. As the sintering temperature elevates, the grain size increases, inducing the improvement of dielectric, ferroelectric and field-induced strain performance. The 1325 °C sintered BCZTNb0.001-0.025BiNZ ceramic thick film has the lowest hysteresis (1.34%) and relatively large unipolar strain (0.104%) at 60 kV/cm, showing relatively large strain and nearly zero strain hysteresis compared with most previously reported lead-free piezoelectric ceramics and presenting favorable application prospects in the actuator field.

High-piezoelectric lead-free BiFeO3–BaTiO3 ceramics with enhanced temperature stability and mechanical properties

BiFeO3–BaTiO3 (BF–BT) ceramics exhibit higher piezoelectric coefficients (d33), Curie temperatures (TC), and temperature stability than other high-temperature lead-free piezoelectric materials. However, despite their crucial role in piezoelectric devices, the mechanical properties of BF–BT ceramics have been underexplored. A thorough evaluation of the mechanical properties of BF–BT is crucial for developing cost-effective and durable lead-free piezoelectric ceramics. Moreover, the specific causes of the high piezoelectric response and excellent temperature stability of BF–BT ceramics remain unclear owing to the instrumental detection threshold, which limits experimental studies to temperatures above 140 °C and below the degradation temperature of d33. To investigate the intrinsic origins of the high piezoelectricity and temperature stability of BF–xBT ceramics and to enhance their mechanical properties, a two-step sintering process is used to fabricate these ceramics (0.25 ≤ x ≤ 0.40). Owing to improvements in grain refinement and reduced Bi3+ volatilization, the BF–0.33BT ceramic exhibits enhanced overall performance, with a modified small punch strength of 155 MPa, Vickers hardness of 5.2 GPa, a d33 of 220 pC/N at room temperature, TC of 466 °C, and d33 values exceeding 400 pC/N at 260 °C. Phase-field simulations, which address the limitations of device detection thresholds, reveal that with increasing temperature, the domain structure relaxes, and polarization intensity decreases. This indicates that changes in the high-temperature piezoelectric properties can be attributed to domain structure relaxation and the increase in dielectric constant. Overall, BF–BT ceramics exhibit superior piezoelectric performance, mechanical properties, and temperature stability, making them highly suitable for use in high-temperature and demanding environments.

Enhanced piezoelectric properties of KNN-based ceramics by synergistic modulation of phase constitution, grain size and domain configurations

Despite significant advancements in KNN-based piezoelectric ceramics, controlling their grain size remains a challenge, impacting reproducibility of piezoelectric properties. Here, we address this issue by initially investigating the defect chemistry of a ternary system 0.96 K0.48Na0.52Nb0.96Sb0.04O3-0.04Bi0.5Na0.5ZrO3-ABO3 (KNNS-BNZ-ABO3). The ABO3 dopant not only influences the phase constitution, but also induces different charge compensation mechanisms, affecting the grain size and domain configurations of ceramics. Furthermore, the relationship between the grain size and the piezoelectric properties is investigated. The superior piezoelectric charge coefficient (d33) of 435 pC/N, ultra-high planar mode electromechanical coupling factor (kp) of 0.62 and preferable temperature stability are obtained in KNN-based ceramics with large grain size (∼50 μm) and hierarchical domain structures. Finally, we elucidated the intrinsic and extrinsic contribution of the grain size on piezoelectric properties of KNN-based piezoceramics based on Rayleigh analysis. Our work provides an effective paradigm for the development of lead-free piezoelectric ceramics for industrial applications.

The structural evolution and electric field-induced strain performance of Bi0.5(Na0.41K0.09)TiO3–Ba(Fe0.5Sb0.5)O3 lead-free piezoelectric ceramics

In recent years, lead-free Bi0.5Na0.5TiO3 (BNT) based piezoelectric ceramics with excellent strain properties have gained widespread recognition for their application in high-precision displacement actuators. The (1-x)(0.82Bi0.5Na0.5TiO3-0.18K0.5Bi0.5TiO3)-xBa(Fe0.5Sb0.5)O3 ceramics were fabricated through the die-pressing method in this work. The effect of BFS introduction on the dielectric, ferroelectric and microstructure characteristics of BNKT ceramics was systematically investigated. Among these compositions, the BNKT-0.015BFS ceramics exhibited a piezoelectric strain coefficient (d33*) of 658 pm/V at an electric field of 55 kV/cm, while achieving a strain response of 0.51 % at 85 kV/cm. The observed improvement in strain performance can be attributed to the evolution from non-ergodic relaxor state to ergodic relaxor state caused by BFS substitution. Furthermore, transmission electron microscopy (TEM) explicitly confirmed coexistence of rhombohedral and tetragonal phase and revealed the morphology of nanosized domains. This study adds to a deeper comprehension of the characteristics of strain response enhancement in BNT-based ceramics, opening up avenues for designing novel lead-free piezoelectric ceramics with outstanding electromechanical performance.

Structure and electrical properties of (1-x)Bi3TiTaO9-xNa0.5Bi2.5Nb2O9 piezoelectric ceramic

The lead-free piezoelectric ceramics (1-x)Bi3TiTaO9–xNa0.5Bi2.5Nb2O9 [(1-x)BTT–xNBN; x = 0.0; 0.2; 0.5; 0.7; 1.0] were prepared using the traditional solid-state method, and the microstructure and electrical properties of the novel solid solution (1-x)BTT–xNBN were studied. XRD data and Raman spectroscopy analysis indicated that Na ions and Nb ions had been incorporated into the designed lattice, forming a stable solid solution. The piezoelectric performance of the (1-x)BTT–xNBN ceramics was improved for two reasons: on one hand, the incorporation of NBN could suppress the leakage current caused by Ti ions, effectively reducing the contribution of oxygen vacancies to the direct current resistivity, thereby increasing the ceramic's direct current resistivity (ρdc); on the other hand, the orthorhombic distortion was reduced, and the remanent polarization was enhanced. Among them, the 0.3Bi3TiTaO9-0.7Na0.5Bi2.5Nb2O9 ceramic demonstrated excellent comprehensive performance: the values of d33, Tc, and Pr were 14.4 pC/N, 777.8 °C, and 9.82 μC/cm2, respectively. Specifically, at 500 °C, tanδ and ρdc were 0.67 % and 1.01 × 108 Ω∙cm, respectively, and after depolarization at 750 °C, its d33 remained at 97.92 % of the original value.

The synthesis and characterization of alkaline niobate-based ceramic composites containing L-lysine Hydrochloride

Some lead-free piezoelectric ceramics are known to have high dielectric and piezoelectric properties but are limited by their brittle nature. A few amino acids have recently been reported to exhibit rather low dielectric and piezoelectric properties but have the advantage of being biocompatible and flexible. It would therefore be interesting to form a composite that will combine the inherent advantage of high dielectric properties from the ceramics and flexibility from the biomolecule. In this research, the properties of lead-free (K0.45Na0.51Li0.04)(Nb0.85Ta0.1Sb0.05)O3 (KNNLST) ceramics and L-lysine hydrochloride (L-LHCl) have been combined to produce dielectric composites. The samples were produced by mixing the constituents from 0 wt.% to 100 wt.%, pelletising and heat-treating them. Bulk density, X-ray diffraction, scanning electron microscopy, and dielectric characterisation were techniques used to determine the density, phases, morphology, and dielectric properties of the produced composites. The results show an increasing bulk density value from 1.2 g/cm3 for L-LHCl to 4.67 g/cm3 for the KNNLST ceramics. The morphology of the composite shows very tiny grains when small amounts of the ceramics were introduced. The L-LHCl transforms from an amorphous phase to a crystalline phase having the orthorhombic-tetragonal structure with the introduction of the KNNLST ceramics. The dielectric constant values increased with increasing KNNLST ceramics content from 10 @1 kHz to 200 for the composite with 80 wt%. KNNLST content. The dielectric loss values decreased for L-LHCl from 0.9 @1 kHz to 0.2 @1kHz. The electrical conductivity values increased with increasing KNNLST ceramics content. The results show that the composites produced from these constituents may be suitable for dielectric applications.

Strain performance and thickness-induced asymmetry in SrTiO3 doped BNT-based lead-free ferroelectrics from nonergodic to ergodic phase

Changes in the relaxation state can greatly affect the electric-field induced strain response in bismuth sodium titanate-based materials. In this work, the strain performances from nonergodic relaxation (NER) to ergodic relaxation (ER) phase transition are investigated by introducing SrTiO3 in (Bi0·5Na0.5)0.98(La0·5Li0.5)0.02TiO3. The solid solutions of perovskite are achieved in all compositions. The ferroelectric to the relaxation phase transition is revealed based on the characteristic peak shape in XRD and temperature dependence of the dielectric properties. The weakened hysteresis of electric-field induced polarization and strain curves results from the creation of localized random fields due to the coexistence of multiple A-site ions, disrupting the ferroelectric long-range ordering at a higher SrTiO3 dopant. The formation of polar nanodomain is promoted and accompanied by the transition from the NER to the ER state. Meanwhile, chemical inhomogeneity is deduced by the anomalous variation in the conduction mechanism and surface state of elemental environments. Asymmetric strain behavior is obtained upon reducing the sample thickness to 0.2 mm, especially pronounced in components with stronger ferroelectricity, where highly asymmetric strain is dominated by surface effect and generated by the non-180° domain switching of the upper and lower surface layers. These features provide insights into the design of strain properties in lead-free piezoelectric ceramics.

Novel Sol-Gel Synthesis Route for Ce- and V-Doped Ba0.85Ca0.15Ti0.9Zr0.1O3 Piezoceramics.

To meet the current demand for lead-free piezoelectric ceramics, a novel sol-gel synthesis route is presented for the preparation of Ba0.85Ca0.15Ti0.9Zr0.1O3 doped with cerium (Ce = 0, 0.01, and 0.02 mol%) and vanadium (V = 0, 0.3, and 0.4 mol%). X-ray diffraction patterns reveal the formation of a perovskite phase (space group P4mm) for all samples after calcination at 800 °C and sintering at 1250, 1350, and 1450 °C, where it is proposed that both dopants occupy the B site. Sintering studies show that V doping allows the sintering temperature to be reduced to at least 1250 °C. Undoped BCZT samples sintered at the same temperature show reduced functional properties compared to V-doped samples, i.e., d33 values increase by an order of magnitude with doping. The dissipation factor tan δ decreases with increasing sintering temperature for all doping concentrations, while the Curie temperature TC increases for all V-doped samples, reaching 120 °C for high-concentration co-doped samples. All results indicate that vanadium doping can facilitate the processing of BCZT at lower sintering temperatures without compromising performance while promoting thermal property stability.

Studies on the compositional dependent structural and electrical properties of CaTiO3-modified K0.5Na0.5NbO3 piezoelectric system

Lead-free piezoelectric ceramics of (1 − x)K0.5Na0.5NbO3-xCaTiO3 were fabricated, and their crystal structure, microstructure, and electrical properties were systematically studied. Rietveld refinement of the x-ray diffraction data and Raman spectroscopic analyses revealed a composition-dependent structural phase transition: three phase transitions, namely, from a pure orthorhombic phase for x ≤ 0.02 to a mixed phase of orthorhombic and tetragonal phases (0.03 ≤ x ≤ 0.08) and finally another mixed phase of tetragonal + cubic for x = 0.10 and 0.15 at room temperature (RT). The morphological study reveals a decrease in grain size along with a more uniform distribution of grains as the concentration of CaTiO3 (CT) increases; notably, a homogeneous distribution of grains is observed for x = 0.05. The temperature-dependent dielectric properties show two phase transitions, from orthorhombic to tetragonal (TO-T) and tetragonal to cubic (TC), for unmodified K0.5Na0.5NbO3 (KNN). However, both the phase transition temperatures (TO-T and TC) decrease, and the transition peaks broaden with an increase in CT substitution, and for x &amp;gt; 0.06, the TO-T shifted below RT. The broadening of the transition peak at TO-T may be due to the relaxation behavior. Among the prepared samples, the 5 mol. % CT-modified KNN shows the optimum electrical properties (d33 = 114 pC/N, ɛr = 412, and 2Pr = 15.25 μC/cm2) at RT. The enhanced electrical properties for x = 0.05 are due to the coexistence of orthorhombic and tetragonal phases, facilitating easy polarization rotation and flattening of the free energy profile. A phase diagram has been constructed based on the information gathered from the temperature-dependent dielectric measurements, RT x-ray diffraction, and Raman spectroscopy data and is discussed in detail.

Ultrahigh Electrobending Deformation in Lead-Free Piezoelectric Ceramics via Defect Concentration Gradient Design.

Recent breakthroughs in defect-engineered lead-free piezoelectric ceramics have reported remarkable electrostrain values, surpassing the limit of lattice distortion. This has aroused wide concern on bending deformation and the associated underlying mechanism. Herein, via designing lead-free piezoelectric ceramics with varying volatilization characteristics, it is uncovered that the ultrahigh electrobending deformation is primarily attributed to a large strain gradient induced by unevenly distributed defect dipoles. In 0.5 mm thick Sr/Sn co-doped potassium sodium niobate ceramics featuring volatile K/Na elements, the inherent bipolar electrostrain value can reach 0.3% at 20kV cm-1 due to the existence of defect dipoles, while the gradient distribution of defect dipole generates significant bending displacement, amplifying apparent electrostrain value to 1.1%. Notably, nonvolatile Ba0.99TiO2.99 ceramic with homogeneous defect dipole distribution does not present electrobending. Of particular interest is that the electrobending phenomenon can be observed through introducing a defect dipole gradient into barium titanate ceramic. A monolayer ceramic with defect dipole gradient can generate large tip displacement (±1.5mm) in cantilever structure, demonstrating its promising potential in precise positioning. This study delves into the underlying mechanism driving electrobending deformation and its impact on the apparent electrostrain measurement in defect-engineered piezoelectric ceramics, providing fresh perspectives for the development of piezoelectric bending actuators.