Na_(0.5)K_(0.5)NbO_3无铅压电陶瓷烧结技术研究进展

Na0.5K0.5NbO3无铅压电陶瓷具有优异的压电性能,是最有希望取代含铅PZT系压电陶瓷的体系之一,但烧结特性差,难以获得高致密度的陶瓷体是制约其研究发展的关键问题。基于近年来有关Na0.5K0.5NbO3无铅压电陶瓷的报道,重点从热压烧结法、放电等离子烧结法、添加烧结助剂法以及添加第二组元促进烧结法四个方面,综述了其在烧结制备技术上取得的研究新进展,并对Na0.5K0.5NbO3无铅压电陶瓷烧结制备技术今后的发展方向提出了一些建议。     

Understanding the piezoelectric properties in potassium-sodium niobate-based lead-free piezoceramics: Interrelationship between intrinsic and extrinsic factors

Lead zirconate titanate (PZT) based ceramics are currently enjoying a wide use in piezoelectric devices despite lead toxicity. Due to growing environmental concerns, the attention on piezoelectric ceramics has been moving to lead-free materials, in particular to (K,Na)NbO₃-based ceramics. Here we report a systematic evaluation of the effects of the compositional modifications on [(K_0.44Na_0.52Li_0.04)[(Nb_0.86Ta_0.10Sb_0.04)_1-xZr_5x/4]O₃ lead–free piezoceramics. We show that an interrelationship between the intrinsic and extrinsic factors is the linchpin for the development of good piezoelectric properties. Hence, the stabilization of the tetragonal symmetry on the orthorhombic-tetragonal polymorphic phase boundary facilities the poling process of the system, thereby enhancing the piezoelectric response. Additionally, the microstructure appears to be related to the piezoelectric properties; i.e., the improved piezoelectric properties correlate to the increase in grain size. The results of this work could help to understand the origin of piezoelectricity in potassium–sodium niobate-based ceramics.     

Growth of Dense Single Crystals of Potassium Sodium Niobate by a Combination of Solid-State Crystal Growth and Hot Pressing

(K_0.5Na_0.5)NbO₃ (KNN) is a potential lead-free replacement for Pb(Zr, Ti)O₃ (PZT) piezoceramics, but its piezoelectric properties are inferior to those of PZT. By growing single crystals of KNN, it may be possible to improve the piezoelectric properties. Recently, single crystals of KNN were grown by the solid-state crystal growth (SSCG) method, but the crystals were very porous. In this paper, a method of growing dense single crystals by SSCG in a hot press will be described. (110)-oriented single seed crystals of KTaO₃ were buried in KNN powder, with 0.5 mol% of K₄CuNb₈O₂₃ added as a sintering aid. After consolidation by uniaxial and isostatic pressing, the tablets were hot pressed in a two-stage treatment. During hot pressing, dense single crystals of KNN grew using the KTaO₃ seed crystal as a template. The effect of hot pressing on single crystal growth will be discussed.     

Insight for the construction of R-T phase boundary in KNN piezoceramics from the view of energy band structure and electron density

The crystal structures and associated energy band structures of classic lead-based PZT (PbZr_0.5Ti_0.5O₃) and lead-free KNN (K_0.5Na_0.5NbO₃) piezoelectric ceramics prepared by a solid-state method are systematically studied based on the First-principles calculations. For better understanding relations between energy band structures and the phase structures in the PbZr_0.5Ti_0.5O₃ and KNN, the components PT (PbTiO₃)/PZ (PbZrO₃) and KN (KNbO₃)/NN (NaNbO₃) are also calculated. The results suggest that the vital contribution to R-T morphotropic phase boundary (MPB) in PbZr_0.5Ti_0.5O₃ comes from the hybridization of A-site and B-site ions, which causes stretching and tilting of oxygen octahedron and therefore leads to the formation of R and T phases. The KNN behaves differently. Moreover, it's concluded that the band structure highly inherited from tetragonal PbTiO₃ plays an important role in the construction of the R-T phase boundary according to the comparison of PbZr_0.5Ti_0.5O₃ and KNN. In general, the work inspires an idea from the view of energy band structure to realize R-T phase coexistence as well as improved piezoelectric properties in KNN-based lead-free piezoceramics.     

Effect of the slurry composition on the piezoelectric properties of PZT ceramics fabricated via materials extrusion 3D printing

Herein, the effect of the binder content in lead zirconate titanate (PZT) slurry has been systematically studied to improve the piezoelectric properties of PZT ceramics prepared via material extrusion 3D printing. For smooth printing, a slurry with a binder concentration ranging from 6 to 12 wt% was proposed. The porosity of the green body first decreased and then increased with an increase in the binder concentration, and the minimum porosity was obtained when the binder concentration reached 10 wt%. Samples with increased density were obtained after debinding and lead-rich atmosphere sintering. PZT piezoceramics fabricated using a binder content of 10 wt% exhibit the maximum relative density (96.9%), largest piezoelectric constant (342.6 pC/N) and dielectric constant (1621). Based on the above process, the wood pile structure and helical twentytetrahedral structural components were successfully fabricated using the material extrusion process. This research lays the foundation for the engineering application of 3D printing to fabricate high-performance piezoceramics with complex shapes.     

Large electric field-induced strain in AgNbO3-modified 0.76Bi0.5Na0.5TiO3-0.24SrTiO3 lead-free piezoceramics

Bi_0.5Na_0.5TiO₃-based lead-free piezoceramics with large strain output are of great importance in the application of piezoelectric actuators. AgNbO₃-modified 0.76Bi_0.5Na_0.5TiO₃-0.24SrTiO₃ (BNT-24ST) lead-free piezoceramics were synthesized by conventional solid-state reaction method. The effects of AgNbO₃ on the structures, dielectric, ferroelectric and piezoelectric properties were carefully investigated. A large electrostrain and normalized strain (d₃₃* = S_max/E_max) of 0.27% and 700?pm/V, were obtained respectively at low electric field (40?kV/cm) for 1?mol.% AgNbO₃-doped BNT-24ST. AgNbO₃ doping modified the phase composition which contained moderate amounts of tetragonal and rhombohedral phase by shifting its T_F-R to below room temperature. Moreover, the reversible field-induced phase transition between relaxor and ferroelectric made contributions to its large strain related properties. This work has confirmed that the actuating performance of BNT-ST-based piezoceramics can be further improved by an easy and cost-effective composition engineering method and showed it a promising candidate for lead-free actuator material.     

Method for Obtaining the Full Set of Linear Electric, Mechanical, and Electromechanical Coefficients and All Related Losses of a Piezoelectric Ceramic

A method based on the use of four piezoelectric resonances for three sample geometries is presented that allows one to obtain all the dielectric permittivities, compliances, and piezoelectric coefficients of a piezoelectric ceramic in complex form and, therefore, all related losses. Piezoelectric losses are responsible for heat generation and hysteresis in actuators. The method is applied to a Navy type II PZT-based piezoelectric ceramic (PZT = lead zirconate titanate), for which the full set of linear electric, mechanical, and electromechanical coefficients is given in complex form. Full sets of coefficients for the available piezoceramics are required for exploiting all the possibilities of finite element analysis, both in fundamental research (mechanisms of degradation) and in development (element design). This numerical technique is necessary to explore arbitrary shapes provided by solid free-form-fabrication technologies.     

Additive manufacturing of lead-free KNN by binder jetting

Additive manufacturing of lead-free piezoceramics is of great interest, given the large request of application-oriented designs with optimal performances and reduced material consumption. Binder Jetting (BJ) is an additive manufacturing technique potentially suited to the production of ceramic components, however the number of feasibility studies on BJ of piezoceramics is extremely limited and totally lacking in the case of sodium-potassium niobate (KNN). In this work, as-synthesised powders are employed in the BJ 3D printing process. Microstructural properties, such as porosity, grain size distributions, and phase composition are studied by SEM, XRD and MIP (Mercury Intrusion Porosimetry) and compared to die-pressed pellets. Analyses reveal considerable residual porosity (~40%) regardless of the printing parameters, with a weak preferential orientation parallel to the printing plane. The piezoelectric characterization demonstrates an outstanding d₃₃ value of 80–90 pC N^?1. Finally, Figures of Merits for the employment as porous piezoceramics in the direct mode are presented.     

国内外压电陶瓷的新进展及新应用

主要综述了近年来国内外压电陶瓷材料的最新进展和最新应用状况,以及为使压电陶瓷材料更充分应用于生产实践中所采取的一系列改性措施,其中包括锆钛酸铅(PZT)压电陶瓷、不含铅的铋层压电陶瓷、钛酸铋钠(BNT)压电陶瓷及钛酸钡(BaTiO3)压电陶瓷系统.最后,还简要介绍了压电陶瓷材料未来的发展趋势.     

Field-insensitive giant dynamic piezoelectric response and its structural origin in (Ba,Ca)(Ti,Zr)O3 tetragonal-orthorhombic phase-boundary ceramics

BaTiO₃ (BT)-based ceramics usually exhibit superior quasi-static piezoelectric response but relatively low electrostrain, which limits their actuator applications. In this study, lead-free (Ba_0.835+xCa_0.165-x)(Ti_0.91Zr_0.09)O₃ (x = 0–0.06) (Ba_xCTZ) ceramics with the compositions close to the tetragonal (T)-rich side of orthorhombic (O)-T polymorphic phase boundary (PPB) were reported to exhibit a field insensitive giant dynamic piezoelectric response (d₃₃* >1050 pm/V) over a wide electric field range up to 2 kV/mm, resulting in the large strain value of ∼0.21 %. Detailed structural investigations combined with various electrical properties measurements reveal that the superior dynamic piezoelectric response is attributed to the combination of piezoelectric effect and domain switching behavior due to the chemical modulated O-T PPB, and the field induced partially irreversible T-O phase transition. The results demonstrate that the studied compositions have great potential for applications of lead-free actuator piezoceramics.     

High piezoelectricity in CuO-modified Ba(Ti0.90Sn0.10)O3 lead-free ceramics with modulated phase structure

High piezoelectricity was achieved in Ba(Ti_0.90Sn_0.10)O₃ lead-free ceramics by optimizing CuO addition and sintering temperature. The phase structure of 1.0 mol% CuO-doped Ba(Ti_0.90Sn_0.10)O₃ ceramic is coexisting rhombohedral and tetragonal phases as sintered at 1300 °C. The coexistence of rhombohedral, tetragonal and orthorhombic phases appears in 1.0 mol% CuO-doped Ba(Ti_0.90Sn_0.10)O₃ ceramics as sintered at 1350–1450 °C, which leads to highly enhanced d₃₃ up to 650pC/N. This work demonstrates that high piezoelectric property (d₃₃ = 650pC/N) can be obtained in BaTiO₃-based lead-free piezoceramics with a simple composition modification by modulating phase structures, which also indicates that Ba(Ti,Sn)O₃ is a promising candidate to replace the lead-based piezoceramics.     

(Na,K)NbO_3基无铅压电陶瓷的研究进展

本文主要综述近几年来国内外有关(Na,K)NbO3基无铅压电陶瓷体系的加压固相烧结技术、液相助烧致密化技术、掺杂改性、相结构调控以及相关机理研究方面的研究进展和动向,并展望该陶瓷体系在医疗超声换能器技术方面的应用前景。     

无铅压电陶瓷材料的研究现状

本文综述了近年来国内外无铅压电陶瓷材料方面的研究进展,重点介绍了钛酸钡基、铋层状结构、钛酸铋钠基、碱金属铌酸盐系以及钨青铜结构无铅压电陶瓷体系的研究现状,并对无铅压电陶瓷的发展作了展望。     

Study of phase transition line of PZT ceramics by X-ray diffraction

The transition line between tetragonal and rhombohedral phases in PZT ceramics has been studied on the basis of X-ray diffraction data, with a view to establishing the morphotropic phase boundary (MPB). In ceramic manufacturing technology, piezoelectric PZT ceramic compositions are most likely to be near the morphotropic phase boundary. This boundary can move when even small levels of dopants are present in the PZT ceramics.     

Phase-composition dependent domain responses in (K0.5Na0.5)NbO3-based piezoceramics

Lead-free (K_0.5Na_0.5)NbO₃-based (KNN) piezoceramics featuring a polymorphic phase boundary (PPB) between the orthorhombic and tetragonal phases at room temperature are reported to possess high piezoelectric properties but with inferior cycling stability, while the ceramics with a single tetragonal phase show improved cycling stability but with lower piezoelectric coefficients. In this work, electric biasing in-situ transmission electron microscopy (TEM) study is conducted on two KNN-based compositions, which are respectively at and off PPB. Our observations reveal the distinctive domain responses in these two ceramics under cyclic fields. The higher domain wall density in the poled KNN at PPB contributes to the high piezoelectric properties. Upon cycling, however, a new microstructure feature, “domain intersection”, is directly observed in this PPB composition. In comparison, the off-PPB KNN ceramic develops large domains during poling, which experience much less extent of disruption during cycling. Our comparative study provides the basis for understanding the relation between phase composition and piezoelectric performance.     

Ultra-high-temperature piezoelectric responses and ultra-high thermal stability of piezoelectricity in ceramic PbZr0.54Ti0.46O3

To date, most piezoceramics with a high piezoelectric coefficient (d₃₃ > 500 pC/N) and a high Curie temperature (T_C around 400°C) are BiScO₃-PbTiO₃-based (BS-PT-based) systems, containing the rare-earth element Sc, whose high cost hinders mass production. We investigated the effect of Nd-doping on the morphotropic phase boundary and synthesized low-cost Nd-doped PbZr_0.54Ti_0.46O₃ (PZT) piezoceramics, achieving high piezoelectric performance. At room temperature, the piezoelectric coefficient d₃₃ reached 550 pC/N with a T_C = 375°C and this changed by only 3.6% over a broad temperature range (30–260°C). The d₃₃ value reached an ultra-high value of 941 pC/N at 345°C, which is higher than that of a BS-PT-based ceramic (810 pC/N at 350°C). The developed PZT ceramic material has a superior electrostrictive strain of 0.45% at 40 kV/cm, and a room temperature piezoelectric coefficient d₃₃* of 1312 pm/V at 20 kV/cm. Our research provides a new paradigm for designing piezoceramics that can be used over a wide temperature range.     

Microscopic origin of the enhanced piezoelectric thermal stability in acceptor doped lead-free Ba(Ti0.8Zr0.2)O3-50(Ba0.7Ca0.3)TiO3 ceramic

Acceptor doping is effective in enhancing thermal stability in piezoceramics, while the reason underlying is still unclear and awaits explanation. In this work, through doping acceptor Mn in lead-free Ba(Ti_0.8Zr_0.2)O₃-50(Ba_0.7Ca_0.3)TiO₃ ceramic, our results show that doping Mn achieves higher depolarization temperature, even higher than Curie temperature (T_C) and simultaneously a better piezoelectric thermal stability. Through microscopic and macroscopic analysis, the enhancement can be explained by the clamping effect induced by acceptor doping, which is carefully demonstrated by symmetry-conforming short-range ordering tendency theory. Thus, this work reveals the mechanism for enhanced depolarization temperature and piezoelectric thermal stability due to acceptor doping and will help developing new thermal stable lead-free piezoceramics applicable in a wider temperature range.     

Life cycle assessment and environmental profile evaluation of lead-free piezoelectrics in comparison with lead zirconate titanate

The prohibition of lead in many electronic components and devices due to its toxicity has reinvigorated the race to develop substitutes for lead zirconate titanate (PZT) based mainly on the potassium sodium niobate (KNN) and sodium bismuth titanate (NBT). However, before successful transition from laboratory to market, critical environmental assessment of all aspects of their fabrication and development must be carried out in comparison with PZT. Given the recent findings that KNN is not intrinsically ‘greener’ than PZT, there is a tendency to see NBT as the solution to achieving environmentally lead-free piezoelectrics competitive with PZT. The lower energy consumed by NBT during synthesis results in a lower overall environmental profile compared to both PZT and KNN. However, bismuth and its oxide are mainly the by-product of lead smelting and comparison between NBT and PZT indicates that the environmental profile of bismuth oxide surpasses that of lead oxide across several key indicators, especially climate change, due to additional processing and refining steps which pose extra challenges in metallurgical recovery. Furthermore, bismuth compares unfavourably with lead due to its higher energy cost of recycling. The fact that roughly 90–95% of bismuth is derived as a by-product of lead smelting also constitutes a major concern for future upscaling. As such, NBT and KNN do not offer absolute competitive edge from an environmental perspective in comparison to PZT. The findings in this work have global practical implications for future Restriction of Hazardous Substances (RoHS) legislation for piezoelectric materials and demonstrate the need for a holistic approach to the development of sustainable functional materials.     

Potassium–Sodium Niobate‐Based Lead‐Free Piezoelectric Ceramic Coatings by Thermal Spray Process

Potassium–sodium niobate (KNN)‐based piezoelectric ceramic coatings with single perovskite phase and dense morphology were obtained by thermal spray processing. The structure, morphology, and properties of the coatings deposited at different conditions were investigated, and excellent piezoelectric performance properties were demonstrated. The piezoelectric coefficient observed in the KNN‐based coatings in this study is about one order of magnitude higher than other thermal sprayed lead‐free piezoelectric coatings as reported in literature. With analyses on the differences in the characteristics between KNN and lead zirconate titanate (PZT) compositions and the reaction mechanisms of thermal spray and ceramic synthesis, the reasons for the successful formation of single‐phase perovskite structure with high crystallinity in the thermal sprayed KNN‐based coatings while not in PZT are explained.     

Micro-stereolithography of KNN-based lead-free piezoceramics

The additive manufacturing technique of micro-stereolithography (µSL) is applied to fabricate alkaline niobate (K_0.48Na_0.52NbO_3, KNN) based lead-free piezoceramics. Complex KNN-based piezoceramic green parts with fine dimensional characteristics, such as a piezoceramic transducer array and a hollow hemisphere, have been printed. The two-step debinding and sintering processes are employed to obtain crack-free dense KNN ceramics with complex shapes. These printed KNN ceramics exhibit superior piezoelectric and ferroelectric performance (ε_r =?2150, d₃₃ =?170?pC/N, P_r =?12.1?μC/cm², E_C =?6.1?kV/cm, and T_C =?230?°C), which are comparable to those of KNN piezoceramics made by traditional methods. These results suggest that the µSL technique may serve as an alternative method to manufacture KNN lead-free piezoceramic components, especially for the application with complex architectures.