Lead-free Piezoelectric Materials Research Articles

Effects of doping with selected rare-earth elements (Eu3+, Dy3+, Eu3+/Dy3+) on the structural characteristics as well as electrical and luminescent properties of K0.5Na0.5NbO3

The effects of adding Eu3+, Dy3+, and Eu3+/Dy3+ rare-earth elements on the microstructural, optical and electrical properties of lead-free piezoelectric materials based on K0.5Na0.5NbO3 (KNN) were investigated. A series of fine powders were synthesized via a modified Pechini route utilizing citric acid. Relatively large amounts of rare-earth elements were successfully incorporated into the crystal lattice of KNN. A combination of X-ray diffraction, X-ray absorption spectroscopy, energy-dispersive X-ray and scanning electron microscopy were used to characterize the structure and chemical composition of the powders and sinters. XRD patterns indicated the formation of a single-phase orthorhombic structure in the co-doped sinter. X-ray absorption spectroscopy revealed the nominal 3+ valence states of Eu and Dy in KNN ceramic sinters. The Mott model and group symmetry theory were used to discuss the characteristics of Raman spectra obtained for the EuDy:KNN ceramics. The ceramics exhibited good dielectric permittivity (ε≃1300) and low dielectric loss (tan δ=0.03) in the temperature range of 170–240°C. The electrical properties of the ceramics showed that the basic mechanism of conduction and relaxation was thermal activation, and that small polaron hopping was responsible for charge carrying. The Eu3+ and Dy3+ ions displayed characteristic red and orange emissions in sinters when excited with light in the wide ultraviolet spectra range (380–420 nm).

The influence of thermo-electromechanical coupling on the performance of lead-free BNT-PDMS piezoelectric composites

In recent times, there have been notable advancements in haptic technology, particularly in screens found on mobile phones, laptops, light-emitting diode (LED) screens, and control panels. However, it is essential to note that the progress in high-temperature haptic applications is still in the developmental phase. Due to their complex phase and domain structures, lead-free piezoelectric materials such as Bi0.5Na0.5TiO3 (BNT)-based haptic technology behave differently at high temperatures than in ambient conditions. Therefore, it is essential to investigate the aspects of thermal management and thermal stability, as temperature plays a vital role in the phase and domain transition of BNT material. A two-dimensional thermo-electromechanical model has been proposed in this study to analyze the thermal stability of the BNT-PDMS composite by analyzing the impact of temperature on effective electromechanical properties and mechanical and electric field parameters. However, the thermo-electromechanical modelling of the BNT-PDMS composite examines the macroscopic effects of the applied thermal field on mechanical and electric field parameters, as phase change and microdomain dynamics are not considered in this model. This study analyzes the impact of thermo-electromechanical coupling on the performance of the BNT-PDMS composite compared to conventional electromechanical coupling. The results predicted a significant improvement in piezoelectric response compared to electromechanical coupling due to the increased thermoelectric effect in the absence of phase change and microdomain switching for temperature boundary conditions below depolarization temperature ( Td∼200∘ C for pure BNT material).

Impact of defect concentration on piezoelectricity in Mn/Fe-doped KTN crystals

Defect engineering via doping exhibits considerable potential for improving the performance of environment-friendly lead-free piezoelectric materials. Owing to the susceptibility to lattice vibrations and the micro-local chemical environment, the readily available Mn/Fe transition metal elements (TMEs) facilitate the construction of defect structures. However, the role of TMEs in shaping the domain structures and the corresponding promotional mechanism of piezoelectricity need to be further decoded. Herein, we propose the different influence mechanisms of Mn and Fe ions on the ferroelectric domain and piezoelectric properties. Different concentrations of (MnNb/Ta′-VO••)• and (FeNb/Ta″-VO••)× defect dipoles are obtained based on the synergy of Mn/Fe ions with oxygen vacancies. Diverse ferroelectric behaviors resulting from (MnNb/Ta′-VO••)• and (FeNb/Ta″-VO••)× defect dipoles are observed. Furthermore, the variation of the dielectric diffusiveness with the defect dipole concentration is investigated. Trace concentration of (MnNb/Ta′-VO••)• generates strong diffusiveness. With the characterization of the ferroelectric domain, this strong diffusiveness is attributed to the lattice-like domain structure. Thereafter, the mechanisms of Mn/Fe defect dipoles on the formation of domain structures are clarified. Macroscopically, the dielectric and piezoelectric properties are measured with Mn/Fe ion components. Trace Mn doping and the resulting lattice-like domain significantly enhance the piezoelectric coefficient, resulting in an increase of nearly 50% for K(Ta,Nb)O3 single crystals. This work highlights the tremendous potential of TME-induced defect dipoles for modifying the ferroelectric domain and provides a reference paradigm for improving piezoelectricity through defect engineering.

Boosting tetracycline degradation of BaTiO3-based piezo-catalysts via modulating phase boundary and band structure

Piezoelectric catalysis, which converts mechanical energy into chemical activity, has important applications in environmental remediation. However, the piezo-catalytic activity of various piezoelectric materials is limited by the weak piezoelectricity as well as the mismatched band-gap, leading to inefficient electron-hole pair generation and difficult carrier migration. Here, a simple strategy combining phase boundary and energy band structure modulation was innovatively proposed to enhance the piezo-catalytic activity of BaTiO3 ferroelectric by Ce ions selecting different doping sites. Thanks to the coexistence of tetragonal (P4mm) and orthorhombic (Amm2) phases effectively flattened the Gibbs free-energy and thus enhanced the piezoelectric activity, as well as suitable energy bandwidth facilitating the carrier migration were realized in the B-sites doped Ba(Ti0.95Ce0.05)O3. The degradation rate constant k of tetracycline (TC) was high to 30.56 × 10-3 min−1, which was 2.03 times higher than that of pure BaTiO3 and superior to most representative lead-free perovskite piezoelectric materials. Theoretical calculations validated that the charge density and high O2 and OH– adsorption energy on the Ba(Ti0.95Ce0.05)O3 surface promoted more efficient •O2– and •OH radicals conversion and bettered response to piezo-catalytic reaction. This work is important to design high-performance piezo-catalysts by synergistic regulation of phase boundary and energy band structure in perovskite materials for long-term antibiotic tetracycline removal.

Investigation of the crystal-oriented behavior of rare earth substituted Sr2NaNb5O15 lead-free piezoelectric materials under a high magnetic field

The crystal-orientation behavior of Sr2NaNb5O15 (SNN) lead-free piezoelectric materials under a magnetic field was investigated by substituting rare-Earth elements (Ln = Nd, Eu, Ho, Yb), which were selected based on their ionic radii and magnetic or non-magnetic ions. The magnetic ions, Nd, Ho, and Yb, did not affect the magnetic anisotropy of the SNN. The nonmagnetic ions (Eu3+) changed from the a, b-axis orientation to the c-axis orientation in the direction of the magnetic field. The Eu-substituted SNN powders revealed that the degree of orientation of the c-axis increased as the Eu content increased. Consequently, c-axis-oriented Eu-substituted SNN ceramics were obtained with the degree of orientation of 0.9. The diamagnetism along the a, b-axis became larger than that along the c-axis owing to a decrease in the c-axis lattice constant. By substituting Eu with SNN, the piezoelectric properties decreased as the hardening of SNN progressed.

Kesan Penggantian Litium ke atas Struktur, Sifat Fizikal dan Sifat Elektrik terhadap Seramik BCZT

The invention of novel lead-free piezoelectric materials with ABO3 perovskite structure, based on barium calcium zirconate titanate (BCZT) for application in various device especially in sensor application. In this work, BCZT with lithium substitution at the calcium site with composition Ba0.85Ca0.15-xLi2xZr0.1Ti0.9O3 (x = 0.00, 0.03, 0.06, 0.09 and 0.12) were synthesized by using the conventional, solid state reaction method. The influence of different Li content on the structure, microstructure, density, and electrical properties were investigated. The results show that substitution led to the improvement of the physical and electrical properties of the piezoelectric ceramic materials. The physical properties show the largest grain size and the highest value of density, ρ which is 4.158 g/cm3 for x = 0.06. This physical properties led to the highest value of piezoelectric coefficient, d33, remnant polarisation, Pr and saturated polarization, Ps which are 304.6 pC/N, 3.27 µC/cm2, and 5.54 µC/cm2, respectively, while the highest dielectric constant, ɛr was 3994 when x = 0.12.

Mesocrystalline SrTiO3/CaTiO3 nanocomposites with 3D heteroepitaxial interfaces, superior piezoresponse and high Curie temperature

Ferroelectric mesocrystalline nanocomposites are promising piezoelectric nanomaterials due to the presence of three-dimensional (3-D) heteroepitaxial interfaces, rendering superior piezoelectric and dielectric responses due to lattice strain at the interface. Herein, we describe the synthesis of mesocrystalline SrTiO3/CaTiO3 (ST/CT) nanocomposites via a two-step topochemical process by using layered titanate H1.07Ti1.73O4·nH2O (HTO), as a precursor, and demonstrate the influence of synthesis parameters on nanostructure, morphology, piezoelectric response and dielectric behavior. The mesocrystalline ST/CT nanocomposites are formed by in-situ topotactic structural transformation, consisting of [110]-oriented ST nanocrystals and [001]-oriented CT nanocrystals with high-density 3-D heteroepitaxial interfaces. The presence of 3-D heteroepitaxial interfaces introduces lattice strain at the interface, leading to an enormously enhanced piezoelectric response with a d33* value of 301 p.m./V. Moreover, the Curie temperature of ST phase is significantly increased from −250 °C to 300 °C by introducing lattice strain. It is demonstrated that the piezoresponse depends on lattice mismatch at heteroepitaxial interfaces and optimal lattice mismatch is found to be ∼3.3%, where the largest lattice strain effect and an expected d33* value of about 450 p.m./V could be achieved. These results demonstrate the potential of lattice strain engineering for high-performance lead-free piezoelectric materials.

Bismuth Ferrite-Based Lead-Free High-Entropy Piezoelectric Ceramics.

Piezoelectric ceramics, as essential components of actuators and transducers, have captured significant attention in both industrial and scientific research. The "entropy engineering" approach has been demonstrated to achieve excellent performance in lead-based materials. In this study, the "entropy engineering" approach was employed to introduce the morphotropic phase boundary (MPB) into the bismuth ferrite (BF)-based lead-free system. By employing this strategy, a serial of novel "medium to high entropy" lead-free piezoelectric ceramics were successfully synthesized, namely (1-x)BiFeO3-x(Ba0.2Sr0.2Ca0.2Bi0.2Na0.2)TiO3 (BF-xBSCBNT, x = 0.15-0.5). Our investigation systematically examined the phase structure, domain configuration, and ferroelectric/piezoelectric properties as a function of conformational entropy. Remarkable performances with a largest strain of 0.50% at 100 kV/cm, remanent polarization ∼40.07 μC/cm2, coercive field ∼74.72 kV/cm, piezoelectric coefficient ∼80 pC/N, and ∼500 pm/V were achieved in BF-0.4BSCBNT ceramics. This exceptional performance can be attributed to the presence of MPB, coexisting rhombohedral and cubic phases, along with localized nanodomains. The concept of high-entropy lead-free piezoelectric ceramics in this study provides a promising strategy for the exploration and development of the next generation of lead-free piezoelectric materials.

Numerical study to compare effective elastic, piezoelectric, and thermal properties of a gyroid triply periodic minimal surface and 0–3 piezoelectric composites with lead-free Ba(Ti 0.8 Zr 0.2)O 3 - x(Ba 0.7 Ca 0.3)Ti O 3 reinforcement

ABSTRACT The present numerical work presents a comparative study of the effective elastic, piezoelectric, and thermal properties of polyvinylidene fluoride (PVDF) matrix and Ba ( T i 0.8 Z r 0.2 ) O 3 − x ( B a 0.7 C a 0.3 ) Ti O 3 (BZT-BCT) reinforcement-based piezo-composite at different volume fractions. The effective properties are significantly influenced by the connectivity of the reinforcement phase within the matrix. In the present work, two types of connectivity have been considered, viz. triply periodic minimal surface (TPMS) interpenetrating phase composite and 0–3 connectivity. Five different volume fractions viz. 10%, 15%, 20%, 25% and 30% were considered. Effective properties were calculated at different volume fractions and for TPMS and 0–3 composite. Significant enhancement in effective properties was observed in TPMS piezo-composites compared to 0–3 piezo-composites. The present work attempts to highlight the importance of connectivity type and the combination of lead-free piezoelectric material BZT-BCT and TPMS reinforcement to achieve better piezoelectric performance.

Lead-Free Piezoelectric Transducers.

Research activities on lead-free piezoelectric materials have been ongoing for over 20 years. Generally, the applicability of the main material families is less universal than that of lead-based compositions such as lead zirconate titanate, but in some cases, the corresponding applications have already been identified. Due to the extensive research, it is now possible to manufacture demonstrators and prototypes for different applications and the authors propose in this article to take stock of these advances. For this, we have chosen to first recall briefly the main new material systems using a simplistic "soft" and "hard" classification for approaching the various resonant transducer applications. Medical imaging applications that represent one of the most important fields are presented in a second step together with other low-power transducers. Then, a variety of applications are merged under the heading of high-power transducers. In addition, we mention two points that are important to consider when manufacturing at a larger scale. For the design of transducers, complete datasets must be available, especially if modeling tools are used. Finally, the commercialization of these lead-free materials imposes essential secondary requirements in terms of availability, reproducibility, sample size, and so on.

Review of Piezoelectric Properties and Power Output of PVDF and Copolymer-Based Piezoelectric Nanogenerators.

The highest energy conversion efficiencies are typically shown by lead-containing piezoelectric materials, but the harmful environmental impacts of lead and its toxicity limit future use. At the bulk scale, lead-based piezoelectric materials have significantly higher piezoelectric properties when compared to lead-free piezoelectric materials. However, at the nanoscale, the piezoelectric properties of lead-free piezoelectric material can be significantly larger than the bulk scale. The piezoelectric properties of Poly(vinylidene fluoride) (PVDF) and Poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) lead-free piezoelectric nanomaterials are reviewed and their suitability for use in piezoelectric nanogenerators (PENGs) is determined. The impact of different PVDF/PVDF-TrFE composite structures on power output is explained. Strategies to improve the power output are given. Overall, this review finds that PVDF/PVDF-TrFE can have significantly increased piezoelectric properties at the nanoscale. However, these values are still lower than lead-free ceramics at the nanoscale. If the sole goal in developing a lead-free PENG is to maximize output power, lead-free ceramics at the nanoscale should be considered. However, lead-free ceramics are brittle, and thus encapsulation of lead-free ceramics in PVDF is a way to increase the flexibility of these PENGs. PVDF/PVDF-TrFE offers the advantage of being nontoxic and biocompatible, which is useful for many applications.

Atomic‐scale insights into electronic, structural, dielectric, and ferroelectric properties of Ba(Zr, Ti)O3 perovskites

Ba(Zr, Ti)O3 perovskites are promising lead-free piezoelectric and relaxor ferroelectric materials for energy storage and harvest devices, of which the ferroelectric mechanism has long been ambiguous. We theoretically investigated the ferroelectric mechanism from the electronic and atomic scale using first-principles calculation based on density functional theory and density functional perturbation theory. With increasing zirconium content, it is obtained a lattice expansion and a decrease in the ferroelectric polarization in agreement with experiment. An unstable zone-center phonon mode is observed in the polar ferroelectric phase, which tends to stabilizein the nonpolar paraelectric phase, which is associated with the engineering of the relative displacement of the B-site ions that alters the short-range force. The newly formed Ti/Zr (dzx,dyz)-O (2px,2py) π-type bonds are discovered to be the origin of the Ba(Zr, Ti)O3ferroelectric instability and polarization. Local relaxation strains caused by lattice misalignment of the ionic displacements of Ti ions and Zr ions suppress the polarization of Ba(Zr, Ti)O3 by counteracting the off-centering of Ti ions and adjacent Zr ions in certain directions.

Ultra-high electro-strain and low hysteresis lead-free piezoelectric ceramics obtained by a novel texture engineering strategy

Two problems plague the field of electro-strain research: low electro-strain performance and high hysteresis. These two key factors are often difficult to optimise simultaneously. Therefore, a novel texture engineering strategy is proposed to obtain ultra-high strain while effectively reducing strain hysteresis. Synergistically optimized textured ceramics with a high degree of orientation in <001> direction were achieved by improving the preparation process based on the conventional TGG method through a heterogeneous template distinct from the ceramic substrate. Finally, the normalized strain of 951 pm/V at 40 kV/cm is obtained in the BNT-based lead-free system, and the strain hysteresis is only 43 %. At the same time, a series of in-situ electric field structural characterization reveal the source of high strain and low hysteresis of the textured ceramics: heterogeneous templates caused high polarization and formed a large number of PNRs. This result is of great significance for the study of electro-strain in lead-free piezoelectric materials and the development of actuators.

Unveiling the polar properties on barium bismuthate perovskite thin films with distinct Ba/Bi ratios

This research aims to investigate the domain structure of BaBiO3 (80:20), BaBiO3 (50:50), and BaBiO3 (30:70) thin films obtained by the polymeric precursor method. For better sample designations, the following codes were employed: (80:20) (BBO82), (50:50) (BBO55), and (30:70) (BBO37). The piezo-ferroelectric coupled behavior observed for barium bismuthates thin films was elucidated in terms of bismuth and oxygen vacancies as well as grain morphology, which can be controlled by stoichiometric changes (Ba/Bi ratios). The films crystallize in a rhombohedral BaBiO3 structure with an R-3R space group without any deleterious secondary phase. Additionally, the hysteretic strain, dielectric, ferroelectric, and piezoelectric properties of BaBiO3 thin films are strongly dependent on the film texture. Sample BBO55 showed a distinguished preferred orientation along the (341) plane with a low associated coercive field (66.87 kV/cm), free of imprint and with no polarizations gap compared to samples BBO37 and BBO82. Sample BBO55 presented the highest piezoelectric (d33-eff ≈ 45.7 pm/V) and ferroelectric (Pr≈19.87 μC/cm2) responses. This behavior can be ascribed to a highly textured film, which generates less strain throughout the crystal lattice, facilitating the polarization switching mechanism and improving piezo/ferroelectricity. These findings are significant for developing novel, high-performance, lead-free piezoelectric materials to be applied in different electronic components such as magnetic field sensors, switches, actuators, and other types of memory devices.

Ultra-high Curie temperature transparent piezoelectric Bi doped Ca2Nb2O7 single crystals

Ca2Nb2O7 is a promising material for high-temperature piezoelectric applications due to its ultra-high Curie temperature, which makes it a suitable candidate for use in harsh environments. However, their piezoelectric performance needs improvement. Here, through chemical engineering methods, we have successfully grown Bi3+ doped Ca2Nb2O7 single crystals using the optical floating zone technique. The Ca1.94Bi0.06Nb2O7 single crystals achieved better high-temperature stability, transparency and a higher piezoelectric constant of 12.8 pC/N at 298 K and 20.0 pC/N at 660 K. In addition to the dopant effects, mechanisms for enhancing the piezoelectric properties of perovskite-like layer structure (PLS) materials have been identified, highlighting the significant contribution of the NbO6 octahedron and interlayer ions. These findings offers valuable insights into improving the performance of PLS materials, which is crucial for promoting their practical applications as high-temperature lead-free piezoelectric materials.

Critical roles of multiphase coexistence in boosting piezo-catalytic activity of BaTiO3-based piezoelectric ceramics

Recently, piezocatalysis induced by perovskite ferroelectric ceramics has widely been favored as a possible fascinating strategy for water remediation due to its low cost, simplicity and feasibility. Herein, a strategy of three-ferroelectric-phase coexistence is proposed to boost the piezocatalytic performance of BaTiO3-based ceramics by introducing Ca(Sn0.5Zr0.5)O3 into BaTiO3. The piezocatalysts of (1-x)BaTiO3–xCa(Sn0.5Zr0.5)O3 ceramics were prepared by a high-temperature solid-phase method. The phase structure, microstructure, electrical properties and catalytic performance of ceramics were comprehensively studied. As x increases from 0 to 0.10, the ceramics undergo the phase evolution from single tetragonal phase to multiphase (coexistence of rhombic, orthorhombic, and tetragonal phases). It is found that the phase structure of the ceramics plays a critical role in enhancing the piezocatalytic activity. The pure BaTiO3 exhibits the tetragonal (T) phase with few spontaneous polarization directions and high polarization rotational energy barrier, resulting in poor catalytic performance and low piezoelectricity. With the coexistence of rhombic (R), orthorhombic (O) and tetragonal (T) phases, the ceramic with x = 0.1 exhibits the increased spontaneous polarization directions and low polarization rotational energy barrier, leading to excellent catalytic performance and high piezoelectricity. Especially, for the ceramics with x = 0.10, the degradation rates of rhodamine B (RhB), methylene blue (MB) and methyl orange (MO) under ultrasonication reach 97 %, 93 % and 73 %, respectively. In addition, the influencing factors of piezocatalytic degradation of RhB and the catalytic mechanism are investigated. This work proposes an environmentally friendly piezoelectric material for improving the water environment and a strategy for improving the catalytic activity of BaTiO3-based lead-free piezoelectric materials.

Modulation of piezoelectricity and mechanical strength in piezoelectric composites based on N0.5B0.51T-BNT nanocubes towards human-machine interfaces

Perceiving mechanical stimuli via piezoelectric nanogenerator (PENG) is attractive for constructing the self-powered sensing system in the field of human-machine interaction. However, the inferior piezoelectricity of the lead-free piezoelectric materials leads to the relatively low sensitivity of PENG. Herein, a 90 nm lead-free off-stoichiometric 0.95Na0.5Bi0.51TiO3-0.05Ba(Ti0.5Ni0.5)O3-δ (N0.5B0.51T-BNT) single crystal was facilely synthesized by hydrothermal method. Compared to stoichiometric 0.95Na0.5Bi0.5TiO3-0.05Ba(Ti0.5Ni0.5)O3–δ, the piezoelectric coefficient presents four folds enhancement, which is associated with the enhanced local structural heterogeneity. By using glass fiber fabric (GFF) as the reinforcing matrix, a mechanically robust PENG based on N0.5B0.51T-BNT is obtained, which delivers a short-circuit current of ∼1.8 μA, and an open-circuit voltage of ∼33.8 V. Meanwhile, the composite film exhibits excellent mechanical strength which can lift the object over 10,000 folds heavier than its own weight successfully. By virtue of the high sensitivity (1.94 V/N, 95.99 nA/N), we assembled the PENG into a 3 * 3 wireless sensing array for the function of the long-distance smart switch and gesture interaction system, which commendably broadens the application scope of the piezoelectric arrays as intelligent sensors.

Superior piezoelectricity in lead-free barium titanate piezoceramics

Since the 21st century, increasing environmental protection and human health concern have been the driving force to develop lead-free piezoelectric materials with enhanced performances, and phase engineering strategy has been validated to be a viable method in numerous methodologies. Here, we gained a superb d33∼(637 ± 30) pC/N in lead-free (1–x)(Ba0.93Ca0.07)(Sn0.08Ti0.92)O3-x(Sb0.5Li0.5)TiO3 [abbreviated as (1–x)BCST-xSLT, 0 ≤ x ≤ 0.4% (in mole)] piezoelectrics utilizing chemical doping. To illustrate the relationship among composition-structure-performance, microstructure characterization, electrical properties measurement, first-principles calculation, and phase-field simulations were performed. Atomic-resolved polarization mapping of z-contrast imaging manifests the ferroelectric three phases (RO–T) coexist at the nanoscale with nanoscale polarization switching among them. Theoretical calculations and simulations confirm that the high-density nano-domain boundary bridges the polyphase coexisting nano-domains, which makes the polarization reversal easy, thus significantly reducing the energy barrier and polarization anisotropy among different phases.

Enhanced Electromechanical Performance in Lead-free (Na,K)NbO3-Based Piezoceramics via the Synergistic Design of Texture Engineering and Sm-Modification.

Next-generation electromechanical conversion devices have a significant demand for high-performance lead-free piezoelectric materials to meet environmentally friendly requirements. However, the low electromechanical properties of lead-free piezoceramics limit their application in high-end transducer applications. In this work, a 0.96K0.48Na0.52Nb0.96Sb0.04O3-0.04(Bi0.5-xSmx)Na0.5ZrO3 (abbreviated as T-NKN-xSm) ceramic was designed through phase regulation and texture engineering, which is expected to solve this difficulty. Through our research, we successfully demonstrated the enhanced electromechanical performance of lead-free textured ceramics with a highly oriented [001]c orientation. Notably, the T-NKN-xSm textured ceramics doped with 0.05 mol % Sm exhibited the optimal electromechanical performance: piezoelectric coefficient d33 ≈ 710 pC N-1, longitudinal electromechanical coupling k33 ≈ 0.88, planar electromechanical coupling kp ≈ 0.80, and Curie temperature Tc ≈ 244 °C. Finally, we conducted a detailed investigation into the phase and domain structures of the T-NKN-Sm ceramics, providing valuable insights for achieving high electromechanical properties in NKN-based ceramics. This research serves as a crucial reference for the development of advanced electromechanical devices by facilitating the utilization of lead-free piezoelectric materials with superior performance and environmental benefits.

Domain reorientation and electric-field-induced phase transition in (K,Na)(Nb,Sb)O3-(Bi,Na)ZrO3 piezoceramics

Polymorphic phase transition boundary (PPB) strategy is effective in designing high-performance piezoelectric materials in (K0.5Na0.5)NbO3 (KNN)-based systems. However, the underlying mechanism of large piezoelectric response in KNN-based is still blurry and thus needs to be explored properly. In this paper, it is found that the domain reorientation becomes easier and more sufficient in the KNN-based ceramics with two-phase coexistence. Moreover, in situ transmission electron microscope experiments disclose the occurrence of a new intermediate phase under an external electric filed, which could relieve the internal stress generated by the domain reorientation and then facilitate the further domain switching along the electric field direction. The enhanced domain reorientation contributes to the high piezoelectric response in PPB region (d33 = 438 pC/N, kp = 48%, d33* = 520 p.m./V at 1.5 kV/mm). Our work provides an in-depth understanding of the contribution of the domain switching and electric-filed-induced phase transition to piezoelectric properties in KNN-based ceramics, which shall benefit the design of new lead-free high-performance piezoelectric materials.