Preparation and piezoelectric properties of potassium sodium niobate glass ceramics

This paper describes the preparation of a piezoelectric glass ceramic material from potassium sodium niobate （Ko.sNa0.sNbO3; KNN） using a novel melting method. The effects of the subsequent heat-treatment on the optical, thermal, electrical, and mechanical properties of the material are carefully examined, and its crystal structure and surface morphol- ogy are characterized respectively by x-ray diffraction and scanning electron microscopy. This new material has a much higher piezoelectric coefficient （163 pC.N-1） than traditional piezoelectric ceramics （131 pC.N-1 ）. On this basis therefore, a strategy for the future study and development of lead-free KNN-based piezoelectric glass ceramics is proposed.

Potassium sodium niobate based lead-free ceramic for high-frequency ultrasound transducer applications

The BiAlO_(3)(BA)and(Bi_(0.5)Na_(0.5))ZrO_(3)(BNZ)are selected to form a solid solution with(K_(0.48)Na_(0.52))NbO_(3) via traditional solid state technique to optimize the electrical performance and temperature stability of KNNbased lead-free ceramics,simultaneously.Here we show that doped BA has a great influence on phase structure,morphologies,and electrical properties.The XRD patterns and dielectric constant versus temperature curves reveal that an increase in the BA content results in a transform of phase structures from a coexistence state of rhombohedral,orthorhombic and tetragonal phases to pseudocubic phase.Owing to the construction of R-O-T phase boundary,optimized performances(T_(C)~336℃,d_(33)~306 pC/N,kp=0.48)are obtained in 0.962(K_(0.48)Na_(0.52))NbO_(3)-0.003BiAlO_(3)-0.035(Bi_(0.5)Na_(0.5))ZrO_(3)(KNN-3)ceramics.Based on the sintered KNN-3 ceramic samples,high-frequency ultrasound imaging transducers are designed and fabricated,which exhibits a high center frequency of 24.5 MHz,a broad -6 dB bandwidth of 97% and a high-sensitivity.Finally,the imaging characteristic of the lead-free transducers is demonstrated via ex vivo imaging of biological tissue structure.As environment friendly materials,the excellent electrical and acoustic performance of developed KNN-based ceramics has great potential for practical applications.

Sodium lithium niobate lead-free piezoceramics for high-power applications:Fundamental,progress,and perspective

With the capability of interconversion between electrical and mechanical energy,piezoelectric materials have been revolutionized by the implementation of perovskite-piezoelectric-ceramic-based studies over 70 years.In particular,the market of piezoelectric ceramics has been dominated by lead zirconate titanate for decades.Nowadays,the research on piezoelectric ceramics is largely driven by cutting-edge technological demand as well as the consideration of a sustainable society.Hence,environmental-friendly lead-free piezoelectric materials have emerged to replace lead-based Pb(Zr,Ti)O_(3)(PZT)compositions.Owing to the inherent high mechanical quality factor(Q_(m))and low energy loss,(Li,Na)NbO_(3)(LNN)materials have recently drawn increasing attention and brought advantages to high-power piezoelectric applications.Although the crystallographic structures of LNN materials were intensively investigated for decades,the technical strategies for electrical performance are still limited.As a result,the property enhancement appears to have approached a plateau.This review traces the progress in the development of LNN materials,starting from the polymorphism in terms of the crystal structures,phase transitions,and local structural distortions.Then,the key milestone works on the functional tunability of LNN are reviewed with emphasis on involved engineering approaches.The exceptional performance at a large vibration velocity makes LNN ceramics promising for high-power applications,such as ultrasonic welding(UW)and ultrasonic osteotomes(UOs).The remaining challenges and some strategic insights for synergistically engineering the functional performance of LNN piezoceramics are also suggested.

Dielectric and piezoelectric perfomance of lead-free ceramics of boron sodium gadolinate niobate at morphotropic phase boundary

New lead-free piezoceramic nanocomposites of Boron Sodium Gadolinium Niobate(BNGN),with general formula(1-x)B_(0.5)Na_(0.5)GdO3xB_(0.5)Na_(0.5)NbO_(3),exhibiting a Morphotropic Phase Boundary(MPB),have been synthesized following hydrothermal method followed by solid state sintering.The occurrence of MPB at the composition with x=0.55,at which rhombohedral and monoclinic phases are found to coexist,has been confirmed using powder XRD.This accounts for the occurrence of large remnant polarization when the sintered ceramic pellets are subjected to electric poling at 2KV/mm.Uniform microstructure of various compositions is confirmed by SEM imaging.Dielectric and piezoelectric properties of the samples are found to be comparable to those of commercial grade PZT.At the MPB,the d_(33)coefficient is found to be 556 pC/N,which is close to that of commercial grade PZT,which makes BNGN a promising material to substitute lead containing PZT in the near future.

Exceptional electrostrain with minimal hysteresis and superior temperature stability under low electric field in KNN-based lead-free piezoceramics

Over the past two decades,(K_(0.5)Na_(0.5))NbO_(3)(KNN)-based lead-free piezoelectric ceramics have made significant progress.However,attaining a high electrostrain with remarkable temperature stability and minimal hysteresis under low electric fields has remained a significant challenge.To address this long-standing issue,we have employed a collaborative approach that combines defect engineering,phase engineering,and relaxation engineering.The LKNNS-6BZH ceramic,when sintered at T_(sint)=1170℃,demonstrates an impressive electrostrain with a d_(33) value of 0.276%and 1379 pm·V^(-1)under 20 kV·cm^(-1),which is comparable to or even surpasses that of other lead-free and Pb(Zr,Ti)O_(3)ceramics.Importantly,the electrostrain performance of this ceramic remains stable up to a temperature of 125℃,with the lowest hysteresis observed at 9.73%under 40 kV·cm^(-1).These excellent overall performances are attributed to the presence of defect dipoles involving V′_(A)-V∙∙_(O) and B′_(Nb)-V∙∙O,the coexistence of R-O-T multiphase,and the tuning of the trade-off between long-range ordering and local heterogeneity.This work provides a lead-free alternative for piezoelectric actuators and a paradigm for designing piezoelectric materials with outstanding comprehensive performance under low electric fields.

High energy storage density in NaNbO_(3) antiferroelectrics with double hysteresis loop

Antiferroelectrics(AFEs)possess great potential for high performance dielectric capacitors,due to their distinct double hysteresis loop with high maximum polarization and low remnant polarization.However,the well-known NaNbO_(3) lead-free antiferroelectric(AFE)ceramic usually exhibits square-like P–E loop related to the irreversible AFE P phase to ferroelectric(FE)Q phase transition,yielding low recoverable energy storage density(Wrec).Herein,significantly improved Wrec up to 3.3 J/cm^(3) with good energy storage efficiency(η)of 42.4% was achieved in Na_(0.7)Ag_(0.3)Nb_(0.7)Ta_(0.3)O_(3)(30Agsingle bond30Ta)ceramic with well-defined double P–E loop,by tailoring the A-site electronegativity with Ag+and B-site polarizability with Ta^(5+).The Transmission Electron Microscope,Piezoresponse Force Microscope and in-situ Raman spectra results verified a good reversibility between AFE P phase and high-field-induced FE Q phase.The improved stability of AFE P phase,being responsible for the double P–E loop and improved Wrec,was attributed to the decreased octahedral tilting angles and cation displacements.This mechanism was revealed by synchrotron X-ray diffraction and Scanning Transmission Electron microscope.This work provides a good paradigm for achieving double P–E loop and high energy storage density in NaNbO_(3)-based ceramics.

Optimizing energy harvesting performance by tailoring ferroelectric/relaxor behavior in KNN-based piezoceramics

Piezoelectric energy harvesters(PEHs)fabricated using piezoceramics could convert directly the mechanical vibration energy in the environment into electrical energy.The high piezoelectric charge coefficient(d_(33))and large piezoelectric voltage coefficient(g_(33))are key factors for the high-performance PEHs.However,high d_(33)and large g_(33)are difficult to simultaneously achieve with respect to g_(33)=d_(33)/(e_(0)e_(r))and d_(33)=2Qe_(0)e_(r)P_(r).Herein,the energy harvesting performance is optimized by tailoring the CaZrO_(3)content in(0.964−x)(K_(0.52)Na_(0.48))(Nb_(0.96)Sb_(0.04))O_(3)-0.036(Bi_(0.5)Na_(0.5))ZrO_(3)-xCaZrO_(3)ceramics.First,the doping CaZrO_(3)could enhance the dielectric relaxation due to the compositional fluctuation and structural disordering,and thus reduce the domain size to~30 nm for x=0.006 sample.The nanodomains switch easily to external electric field,resulting in large polarization.Second,the rhombohedral-orthorhombic-tetragonal phases coexist in x=0.006 sample,which reduces the polarization anisotropy and thus improves the piezoelectric properties.The multiphase coexistence structures and miniaturized domains contribute to the excellent piezoelectric properties of d_(33)(354 pC/N).Furthermore,the dielectric relative permittivity(ε_(r))reduces monotonously as the CaZrO_(3)content increases due to the relatively low ion polarizability of Ca^(2+)and Zr^(4+).As a result,the optimized energy conversion coefficient(d_(33)×g_(33),5508×10^(−15)m^(2)/N)is achieved for x=0.006 sample.Most importantly,the assembled PEH with the optimal specimen shows the excellent output power(~48 mW)and lights up 45 red commercial light-emitting diodes(LEDs).This work demonstrates that tailoring ferroelectric/relaxor behavior in(K,Na)NbO_(3)-based piezoelectric ceramics could effectively enhance the electrical output of PEHs.

Multi-phase structure and electrical properties of Bi_(0.5)Li_(0.5)ZrO_3 doping K_(0.48)Na_(0.56)NbO_3 lead-free piezoelectric ceramics

(1–x)K_(0.48)Na_(0.56)NbO_3–xBi_(0.5)Li_(0.5)ZrO_3(KNN–x BLZ, x = 0–0.06) lead-free piezoelectric ceramics were prepared by the conventional solid-state sintering method, and their phase structures and electric properties as well as T_C were systematically investigated. The orthorhombic–tetragonal(O–T) two phases were detected in all(1–x)K_(0.48)Na_(0.56)NbO_3–xBi_(0.5)Li_(0.5)ZrO_3 ceramics at 0.01 ≤ x ≤ 0.05. Due to the appropriate ratio between O phase and T phase(CO/C T= 45/55), high piezoelectric properties of d 33= 239 pC/N, k_p= 34%, and P_r = 25.23 μC/cm^2 were obtained at x = 0.04. Moreover, a high T_C = 348 ℃ was also achieved in KNN–x BLZ ceramic at x = 0.04. These results indicate that (1–x)K_(0.48)Na_(0.56)NbO_3–xBi_(0.5)Li_(0.5)ZrO_3 system is a promising candidate for high-temperature piezoelectric devices.

A REVIEW ON LEAD-FREE PIEZOELECTRIC CERAMICS STUDIES IN CHINA

There are a large number of research publications on the hot topic of environmental friendly leadfree piezoelectric materials worldwide in the last decade.The number of researchers and institutions involved from China is much larger than other countries or regions.The publications by Chinese researchers cover a broad spectrum on the preparations,structures,properties and applications of lead-free piezoelectric ceramics.This has motivated us to come out with a review on recent advances in development of lead-free piezoelectric ceramics in China.The emphases are especially on the preparation and electric properties of barium titanate-based materials,bismuth sodium titanate and related materials,alkaline niobate and related materials,bismuth layerstructured materials,as well as texture engineering of ceramics and some of their single crystals.Hopefully,this could give further impetus to the researchers to continue their e®orts in this promising area and also draw the attentions from legislature,research o±ce,industrial and publics.

Electrical properties and luminescence properties of 0.96(K0.48Na0.52)(Nb0.95Sb0.05)–0.04Bi0.5(Na0.82K0.18)0.5ZrO3–xSm lead-free ceramics

In this paper,Sm-doped 0.96(K0.48 Na0.52)(Nb0.95 Sb0.05)–0.04 Bi0.5(Na0.82 K0.18)0.5 Zr O3(abbreviated as KNSN–0.04 BNKZ)lead-free piezoelectric ceramics were prepared by conventional solid-state sintering method and the effects of Sm2 O3 on the phase structure,microstructure,electrical and luminescent properties of KNSN–0.04 BNKZ potteries were studied.Results revealed that a single solid solution phase with pseudo-cubic perovskite structure was formed between KNSN–0.04 BNKZ and Sm2 O3.Existence of weak dielectric/ferroelectric properties with a diffuse dielectric anomaly and slim P–E hysteresis loops of the Sm-doped KNSN–0.04 BNKZ demonstrated the ferroelectric relaxor behavior of the KNNS–0.04 BNKZ–x Sm ceramics.Accordingly,the temperature stability and fatigue behavior of the modified ceramics were significantly improved.It was found that the KNSN–0.04 BNKZ ceramics with 0.002 mol Sm addition exhibited nearly temperature independent properties and fatigue-free behavior.Moreover,Sm-modified KNSN–0.04 BNKZ exhibits a bright photoluminescence with a strong orange emission under visible light irradiation.As a material with both electrical and luminescent properties,it has good application prospect in future optoelectronic components by integrating its luminescent and electrical properties.

Effects of Ge4＋ acceptor dopant on sintering and electrical properties of （K0.5Na0.5）NbO3 lead-free piezoceramics

Lead-free （K0.5Na0.5）（Nb1-xGex）O3 （KNN-xGe, where x = 0-0.01） piezo- electric ceramics were prepared by conventional ceramic processing. The effects of Ge4＋cation doping on the phase compositions, microstructure and electrical properties of KNN ceramics were studied. SEM images show that Ge4＋ cation doping improved the sintering and promoted the grain growth of the KNN ceramics. Dielectric and ferroelectric measurements proved that Ge4＋ cations substituted Nbs＋ ions as acceptors, and the Curie temperature （Tc） shows an almost linear decrease with increasing the Ge4＋ content. Combining this result with microstructure observations and electrical measurements, it is concluded that the optimal sintering temperature for KNN-xGe ceramics was 1020℃. Ge4＋ doping less than 0.4 mol.% can improve the compositional homogeneity and piezoelectric properties of KNN ceramics. The KNN-xGe ceramics with x = 0.2% exhibited the best piezoelectric properties： piezoelectric constant d33 = 120 pC/N, planar electromechanical coupling coefficient kp = 34.7%, mechanical quality factor Qm = 130, and tanδ = 3.6%.

Improvement in synthesis of （K0.5Na0.5）NbO3 powders by Ge4＋ acceptor doping

In this paper, the effects of doping with GeO2 on the synthesis temperature, phase structure and morphology of （K0.5Na0.5）NbO3 （KNN） ceramic powders were studied using XRD and SEM. The results show that KNN powders with good crystallinity and compositional homogeneity can be obtained after calcination at up to 900℃ for 2 h. Introducing 0.5 mol.% GeO2 into the starting mixture improved the synthesis of the KNN powders and allowed the calcination temperature to be decreased to 800℃, which can be ascribed to the formation of the liquid phase during the synthesis.

BiCoO3-doped （Ko.47sN ao.47sLio.os）（N bo.8Tao.2）03 lead-free piezoelectric ceramics

（1-x）（K0.47sNa0.475Li0.os）（Nb0.sTa0.2）O3-xBiCoO3 （KNLNT-BC） lead-free piezoelectric ceramics were prepared by the conventional solid-state sintering method. Effects of the BC content on the phase structure, microstructure and electrical properties of KNLNT-BC ceramics were investigated. XRD patterns reveal that all the ceramic samples are in the pure perovskite-type structure, and the phase structure changes from the tetragonal to pseudo-cubic phase with the increase of the BC content. After the substitution of BC, the grain size is significantly reduced and relaxer behaviors are induced. By adding a small amount of BC to KNLNT ceramics, piezoelectric properties are improved, while further addition of BC makes the piezoelectric properties deteriorate markedly. The optimized electrical properties atx= 0.005 are as follows： d33 = 194 pC/N, kp = 0.44.

Flexible and self-powered blinking and eyeball movements sensing based on electrospun lead-free piezoelectric nanofibers

Potassium sodium niobate(KNN)-based nanofibers could combine piezoelectric properties with exceptional flexibility and biocompatibility,making them highly promising for flexible sensors in electronic skin and wearable applications.However,the suboptimal piezoelectric performance limits their sensitivity in detecting minute human body motions,such as blinking and eye movements.Herein,Li and Ta-doped KNN nanofibers were fabricated via an electro-spinning process.Co-doping with 6%Li at the A-site and 30%Ta at the B-site induces lattice distortion and an orthorhombic(O)to tetragonal(T)phase transition in the electrospun nanofibers,resulting in a significantly enhanced piezoelectric response,with an average d_(33)*value reaching 110.7 pm/V.The outstanding piezoelectric response gives rise to a remarkable sensitivity(0.3365 V/(N cm^(2)))in a self-powered flexible pressure sensor based on the doped KNN nanofibers,encapsulated in a polydimethylsiloxane matrix.The sensors,when attached to the temple regions,can detect tiny facial motions induced by blinking,enabling the distinction of abnormal blinking patterns associated with mental fatigue and excessive eye use.Additionally,they support real-time,continuous,and unobtrusive eyeball tracking,highlighting their potential as critical components in human-computer interaction and artificial intelligence applications.