Temperature Stability of V2O5-Doped KNN-LS-BF Lead-Free Piezoelectric Ceramics

V₂O₅-doped Na_0.5K_0.5NbO₃-LiSbO₃-BiFeO₃ (KNN-LS-BF) lead-free piezoelectric ceramics were prepared by the traditional sintering method, and their temperature stability was studied. Characterization of the temperature dependences of dielectric and piezoelectric properties of the V₂O₅-doped KNN-LS-BF ceramics showed that V₂O₅ doping could significantly improve the temperature stability in the temperature range of 30°C to 420°C and cause a downward shift in the orthorhombic–tetragonal phase transition to below room temperature. It was also found that the V₂O₅-doped KNN-LS-BF ceramics possess good dielectric and piezoelectric properties (ε _r > 1066, tan δ < 4%, d ₃₃ > 185 pC/N, k _p > 0.25) in the temperature range of 30°C to 300°C.     

Bi改性铌酸钾钠基无铅压电陶瓷的温度稳定性

铌酸钾钠基压电陶瓷(Na0.53K0.41Li0.06)Nb0.955Sb0.045O3的正交–四方多型相变在室温附近,具有良好的压电性能,但其温度稳定性很差。通过掺杂Bi2O3,使该陶瓷的正交–四方多型相变温度tO-T从15℃降低到了–9℃,同时保持了较高的居里温度tC(368℃),从而显著改善了其压电性能的温度稳定性。由于Bi3+施主掺杂作用和Sb5+较强的电负性,改性后的陶瓷保持了优良的电学性能:d33=213pC/N,kp=0.441,ε3T3=1319,tanδ=0.016。     

MBi_4Ti_4O_(15)基陶瓷的研究现状与发展趋势

铋层状结构无铅铁电陶瓷具有良好的抗疲劳性能和较高的居里温度,在铁电存储以及高温压电器件方面具有广阔的应用前景。介绍了MBi4Ti4O15基铋层状陶瓷的结构特点,综述了微量元素掺杂、粉体制备方法和晶粒定向技术对该陶瓷铁电压电性能的影响。并展望了MBi4Ti4O15基铋层状无铅铁电陶瓷未来的发展趋势。     

Field-Induced Multiscale Polarization Configuration Transitions of Mesentropic Lead-Free Piezoceramics Achieving Giant Energy Harvesting Performance

The development of high-performance (K,Na)NbO₃ (KNN)-based lead-free piezoceramics for next-generation electronic devices is crucial for achieving environmentally sustainable society. However, despite recent improvements in piezoelectric coefficients, correlating their properties to underlying multiscale structures remains a key issue for high-performance KNN-based ceramics with complex phase boundaries. Here, this study proposes a medium-entropy strategy to design “local polymorphic distortion” in conjunction with the construction of uniformly oversize grains in the newly developed KNN solid-solution, resulting in a novel large-size hierarchical domain architecture (≈0.7 µm wide). Such a structure not only facilitates polarization rotation but also ensures a large residual polarization, which significantly improves the piezoelectricity (≈3.2 times) and obtains a giant energy harvesting performance (W_out = 2.44 mW, P_D = 35.32 µW mm⁻³, outperforming most lead-free piezoceramics). This study confirms the coexistence of multiphase through the atomic-resolution polarization features and analyzes the domain/phase transition mechanisms using in situ electric field structural characterizations, revealing that the electric field induces highly effective multiscale polarization configuration transitions based on T–O–R sequential phase transitions. This study demonstrates a new strategy for designing high-performance piezoceramics and facilitates the development of lead-free piezoceramic materials in energy harvesting applications.     

Diffused Phase Transition Boosts Thermal Stability of High‐Performance Lead‐Free Piezoelectrics

High piezoelectricity of (K,Na)NbO₃ (KNN) lead‐free materials benefits from a polymorphic phase transition (PPT) around room temperature, but its temperature sensitivity has been a bottleneck impeding their applications. It is found that good thermal stability can be achieved in CaZrO₃‐modified KNN lead‐free piezoceramics, in which the normalized strain d ₃₃* almost keeps constant from room temperature up to 140 °C. In situ synchrotron X‐ray diffraction experiments combined with permitivity measurements disclose the occurrence of a new phase transformation under an electrical field, which extends the transition range between tetragonal and orthorhombic phases. It is revealed that such an electrically enhanced diffused PPT contributed to the boosted thermal stability of KNN‐based lead‐free piezoceramics with high piezoelectricity. The present approach based on phase engineering should also be effective in endowing other lead‐free piezoelectrics with high piezoelectricity and good temperature stability.     

Investigation of Structural and Electrical Properties of B-Site Complex Ion (Mg1/3Nb2/3)4+-Modified High-Curie-Temperature BiFeO3-BaTiO3 Ceramics

B-site complex ion (Mg_1/3Nb_2/3)-modified high-temperature ceramics 0.71BiFeO₃-0.29BaTi_1?x (Mg_1/3Nb_2/3) _x O₃ (BF-BTMNx) have been fabricated by the conventional solid-state reaction method. The compositional dependence of the?phase structure, electrical properties, and depolarization temperature of the ceramics was studied. The main phase structure of BF-BTMNx ceramics is perovskite phase with pseudocubic symmetry. The experimental results show that the dielectric and piezoelectric properties, and temperature stability strongly depend on the (Mg_1/3Nb_2/3)⁴⁺ content. The optimum (Mg_1/3Nb_2/3) content enhances the piezoelectric properties, Curie temperature, and depolarization temperature. The ceramic with x = 1% exhibited enhanced electrical properties of d ₃₃ = 158 pC/N and k _p = 0.322, combined with high-temperature stability with Curie temperature of T _c = 453°C and depolarization temperature of T _d = 400°C. These results show that the ceramic with x = 1% is a promising lead-free high-temperature piezoelectric material.     

Boosting Piezoelectricity by 3D Printing PVDF-MoS2 Composite as a Conformal and High-Sensitivity Piezoelectric Sensor

Additively manufactured flexible and high-performance piezoelectric devices are highly desirable for sensing and energy harvesting of 3D conformal structures. Herein, the study reports a significantly enhanced piezoelectricity in polyvinylidene fluoride (PVDF) achieved through the in situ dipole alignment of PVDF within PVDF-2D molybdenum disulfide (2D MoS₂) composite by 3D printing. The shear stress-induced dipole poling of PVDF and 2D MoS₂ alignment are harnessed during 3D printing to boost piezoelectricity without requiring a post-poling process. The results show a remarkable, more than the eight-fold increment in the piezoelectric coefficient (d₃₃) for 3D printed PVDF-8wt.% MoS₂ composite over cast neat PVDF. The underlying mechanism of piezoelectric property enhancement is attributed to the increased volume fraction of β phase in PVDF, filler fraction, heterogeneous strain distribution around PVDF-MoS₂ interfaces, and strain transfer to the nanofillers as confirmed by microstructural analysis and finite element simulation. These results provide a promising route to design and fabricate high-performance 3D piezoelectric devices via 3D printing for next-generation sensors and mechanical–electronic conformal devices.     

Effects of Sintering Temperature on Structure and Properties of 0.997(KNN-LS-BF)-0.003V2O5 Lead-Free Piezoelectric Ceramics

0.997(KNN-LS-BF)-0.003V₂O₅ lead-free piezoelectric ceramics were prepared by a traditional sintering method. The effects of sintering temperature on the structure and properties of the 0.997(KNN-LS-BF)-0.003V₂O₅ ceramics were studied. The results show that the sintering temperature exerts a distinct influence on the phase structure and properties. With the increase in sintering temperature from 1040°C to 1060°C, the main crystallographic phase changes from the orthorhombic symmetry to the tetragonal phase, and the optimum dielectric and piezoelectric properties of samples can be obtained when sintering at 1060°C. However, the dielectric and piezoelectric properties of the samples deteriorate when the sintering temperature exceeds 1060°C.     

高温无铅压电材料研究进展

随着航空航天、石油化工等领域的快速发展以及可持续发展战略的实施,高温无铅压电材料的作用愈发重要。该文总结了具有高居里温度点无铅压电材料的研究进展,主要包括钙钛矿型的BiFeO₃基和BiAlO₃基陶瓷、铋层状陶瓷、钙钛矿层状结构陶瓷以及铌酸锂、硅酸镓镧和硼酸氧钙稀土等压电单晶。最后总结了目前高温无铅压电材料中存在的问题,并提出其发展方向。     

The Biaxial Strain Dependence of Magnetic Order in Spin Frustrated Mn3NiN Thin Films

Multicomponent magnetic phase diagrams are a key property of functional materials for a variety of uses, such as manipulation of magnetization for energy efficient memory, data storage, and cooling applications. Strong spin‐lattice coupling extends this functionality further by allowing electric‐field‐control of magnetization via strain coupling with a piezoelectric. Here this work explores the magnetic phase diagram of piezomagnetic Mn₃NiN thin films, with a frustrated noncollinear antiferromagnetic (AFM) structure, as a function of the growth induced biaxial strain. Under compressive strain, the films support a canted AFM state with large coercivity of the transverse anomalous Hall resistivity, ρ_xy, at low temperature, that transforms at a well‐defined Néel transition temperature (T_N) into a soft ferrimagnetic‐like (FIM) state at high temperatures. In stark contrast, under tensile strain, the low temperature canted AFM phase transitions to a state where ρ_xy is an order of magnitude smaller and therefore consistent with a low magnetization phase. Neutron scattering confirms that the high temperature FIM‐like phase of compressively strained films is magnetically ordered and the transition at T_N is first‐order. The results open the field toward future exploration of electric‐field‐driven piezospintronic and thin film caloric cooling applications in both Mn₃NiN itself and the broader Mn₃AN family.     

High‐Temperature BiScO3‐PbTiO3 Piezoelectric Vibration Energy Harvester

Conventionally, effective mechanical vibration energy harvesting is based on (Pb,Zr)TiO₃ (PZT) ceramics, poly(vinylidene fluoride) (PVDF) polymers or PVDF/PZT or other piezoelectric composite materials, and their working temperature is normally limited to room temperature (R‐T) or below 150 °C. Here, bismuth scandium lead titanate (BiScO₃‐PbTiO₃, abbreviated as BSPT) ceramic is reported which has a high Curie temperature point around 450 °C and its application for high‐temperature (H‐T) vibration energy harvesting. Experimental results show that it exhibits an excellent H‐T piezoelectricity, converting mechanical vibration energy into electric power effectively in a wide temperature range from R‐T till 250 °C. This research shows the BSPT piezoelectric energy harvester having the potential application for self‐power source of wireless sensor network system in high temperature circumstance.     

Domain Engineering of Lead‐Free Li‐Modified (K,Na)NbO3 Polycrystals with Highly Enhanced Piezoelectricity

Aging and re‐poling induced enhancement of piezoelectricity are found in (K,Na)NbO₃ (KNN)‐based lead‐free piezoelectric ceramics. For a compositionally optimized Li‐doped composition, its piezoelectric coefficient d₃₃ can be increased up to 324 pC N^?1 even from a considerably high value (190 pC N^?1) by means of a re‐poling treatment after room‐temperature aging. Such a high d₃₃ value is only reachable in KNN ceramics with complicated modifications using Ta and Sb dopants. High‐angle X‐ray diffraction analysis reveals apparent changes in the crystallographic orientations related to a 90° domain switching before and after the aging and re‐poling process. A possible mechanism considering both defect migration and rotation of spontaneous polarization explains the experimental results. The present study provides a general approach towards piezoelectric response enhancement in KNN‐based piezoelectric ceramics.     

Giant Piezoelectricity of Ternary Perovskite Ceramics at High Temperatures

Here, novel ferroelectric ceramics of (0.95 ? x)BiScO₃‐xPbTiO₃‐0.05Pb(Sn_1/3Nb_2/3)O₃ (BS‐xPT‐PSN) of complex perovskite structure are reported with compositions near the morphotropic phase boundary (MPB), and which exhibit a piezoelectric coefficient d₃₃ = 555 pC N^?1, a large‐signal coefficient $d_{33}^{?}$ ≈ 1200 pm V^?1 at room temperature, and a high Curie temperature T_C of 408 °C. More interestingly, this ternary system exhibits a giant and stable piezoelectric response at 200 °C with a large‐signal $d_{33}^{?}$ ≈ 2500 pm V^?1, matching that of the costly relaxor‐based piezoelectric single crystals at room temperature. The mechanisms of such giant piezoelectricity and its characteristic temperature dependence are attributed to the spontaneous polarization rotation and extension under an electric field and the MPB‐related phase transition. The findings reveal that the BS‐xPT‐PSN ceramics constitute a new family of high‐performance piezoelectric materials suitable for electromechanical transducers that can be operated at high temperatures (at 200 °C, or higher).     

Grain Boundary Diffusion Hardening in Potassium Sodium Niobate-Based Ceramics with Full Gradient Composition and High Piezoelectricity

Reducing mechanical losses and suppressing self-heating are critical characteristics for high-power piezoelectric applications. For environmentally friendly Pb-free piezoelectric ceramics, traditional acceptor doping or annealing treatments have successfully improved the mechanical quality factor (Q_m) based on a ceramic matrix with a poor piezoelectric coefficient (d₃₃<100 pC/N). Nevertheless, a ceramic with high Q_m and d₃₃ values has not been reported owing to the inverse relationship between Q_m and d₃₃. Herein, a novel hardening method called grain boundary diffusion is used to develop Pb-free potassium sodium niobate ceramics, where Q_m increased by more than two-fold (from 51 to 132) and a high d₃₃ value (d₃₃ = 360 pC/N) is maintained. Significantly, d₃₃ retained 98% of its initial value after 180 days, exhibiting improved aging stability. The established properties are associated with the formation of the core-shell microstructure and the full gradient composition distribution using structural characterizations and phase-field simulations, where the core maintains a high d₃₃ and the shell provides a hardening effect. The novel hardening effect in piezoelectric materials, known as grain boundary diffusion hardening, highlights the enhancement of the mechanical quality factor with high piezoelectricity, providing a new paradigm for the design of functional materials.     

Giant Electric Field-Induced Strain with High Temperature-Stability in Textured KNN-Based Piezoceramics for Actuator Applications

Large-strain (K,Na)NbO₃ (KNN) based piezoceramics are attractive for next-generation actuators because of growing environmental concerns. However, inferior performance with poor temperature stability greatly hinders their industrialized procedure. Herein, a feasible strategy is proposed by introducing ${\mathrm{V}}_{\text{K/Na}}^{{}^{\prime }}$-${\mathrm{V}}_{\stackrel{\mathrm{..}}{\mathrm{O}}}$ defect dipoles and constructing grain orientation to enhance the strain performance and temperature stability of KNN-based piezoceramics. This textured ceramics with 90.3% texture degree exhibit a giant strain (1.35%) and a large converse piezoelectric coefficient d₃₃^* (2700 pm V⁻¹), outperforming most lead-free piezoceramics and even some single crystals. Meanwhile, the strain deviation at high temperature of 100 °C–200 °C is obviously alleviated from 61% to 35% through texture engineering. From the perspective of practical applications, piezo-actuators are commonly utilized in the form of multilayer. In order to illustrate the applicability on multilayer actuators, a stack-type actuator consisted of 5 layers of 0.4 mm thick ceramics is fabricated. It can generate large field-induced displacement (11.6 µm), and the promising potential in precise positioning and optical modulation are further demonstrated. This work provides a textured KNN-based piezoceramic with temperature-stable giant strain properties, and facilitates the lead-free piezoceramic materials in actuator applications.     

Zn-B玻璃掺杂的(K0.5Na0.44Li0.06)(Nb0.84Ta0.1Sb0.06)O3陶瓷相变及电学性能研究

研究了Zn-B玻璃掺杂的(K0.5Na0.44Li0.06)(Nb0.84Ta0.1Sb0.06)O3(KNLNTS)陶瓷的制备、相变及电学性能.研究发现,Zn-B玻璃能够有效地促进铌酸钾钠基无铅压电陶瓷的烧结特性.XRD结果显示Zn-B玻璃掺杂的KNLNTS陶瓷为正交-四方共存结构,随掺杂量的增加正交结构相的含量逐渐增加;并且降低烧结温度能够有效地抑制第二相的产生.介电温谱测试结果显示Zn-B玻璃掺杂的KNLNTS陶瓷其居里温度先降后增在x=0.1时达到最小值.在1050℃保温5 h条件下烧结可以获得最佳的压电性能:d33=197 pC/N,kp=0.37,εr=975,tanδ=0.028.     

Enhanced Piezoelectric Properties and Tunability of Lead-Free Ceramics Prepared by High-Energy Ball Milling

Zirconium-doped barium titanate Ba(Zr_0.15Ti_0.85)O₃ lead-free ceramics (hereinafter referred to as BZT) were synthesized using the solid-state reaction method by adopting the high-energy ball milling technique. Nanosized BZT powders resulted from high-energy ball milling, which in turn enhanced the dielectric and piezoelectric properties of the ceramics. A single-phase perovskite structure free from secondary phase peaks was observed for sintered BZT samples, and a relative density of ～94% of the theoretical density was achieved. The electric-field-induced polarization-current data indicate the ferroelectric nature of the samples. Unipolar strain as high as 0.12% was realized for the ceramics sintered at 1350°C, indicating their potential for use in actuator applications. Very high tunability of >70% for these ceramics is also reported.     

压电器件用KNN基无铅压电陶瓷的研究进展

(K, Na)NbO₃(KNN)基无铅压电陶瓷作为一种环境友好型材料,兼具较高的居里温度和可调控的相界结构,在压电器件领域展示出潜在的应用前景,引起了广泛关注和大量研究。对其物相组成、制备工艺、性能调控等方面的研究进展进行了评述,并重点介绍了其在压电器件领域的实际应用,最后对KNN及其在器件应用方面未来的研究和发展方向进行了总结展望。     

Temperature‐Insensitive (K,Na)NbO3‐Based Lead‐Free Piezoactuator Ceramics

The development of lead‐free piezoceramics has attracted great interest because of growing environmental concerns. A polymorphic phase transition (PPT) has been utilized in the past to tailor piezoelectric properties in lead‐free (K,Na)NbO₃ (KNN)‐based materials accepting the drawback of large temperature sensitivity. Here a material concept is reported, which yields an average piezoelectric coefficientd₃₃ of about 300 pC/N and a high level of unipolar strain up to 0.16% at room temperature. Most intriguingly, field‐induced strain varies less than 10% from room temperature to 175 °C. The temperature insensitivity of field‐induced strain is rationalized using an electrostrictive coupling to polarization amplitude while the temperature‐dependent piezoelectric coefficient is discussed using localized piezoresponse probed by piezoforce microscopy. This discovery opens a new development window for temperature‐insensitive piezoelectric actuators despite the presence of a polymorphic phase transition around room temperature.     

Defect Dipole-Induced Fatigue Strain Recoverability in Lead-Free Piezoelectric Ceramics

Piezoelectric ceramics have garnered extensive utilization in high-precision actuators, where the magnitude of electric field-induced strain and fatigue resistance play crucial roles in actuation applications. Herein, an innovative strategy based on defect dipoles is proposed to form a defect-engineered polymorphic phase transition and achieve a giant piezoelectric strain coefficient of 3080 pm V⁻¹ in Li/Sr-doped (K_0.5Na_0.5)NbO₃ lead-free piezoceramics. The mechanism responsible for the enhanced strain performance lies in the optimized strain compatibility between the refined stripe domains and the nanosized domains. Additionally, the results demonstrate that the material is able to recover from fatigue-induced strain depletion under the stimulation of bipolar electric fields. This property can be phenomenologically explained by the rigid ion model, in which the application of reversal electric fields can facilitate the restoration of defect dipoles, thereby greatly contributing to strain recoverability. This study establishes a close correlation between the unipolar strain properties and the inherent flexibility of defect dipoles and provides new insight into the design of high-reliability, large-stroke piezoceramics.