Influence of Composition on Properties of BNT-BT Lead-Free Piezoceramics

Lead-free piezoelectric ceramics of (Bi1/2Na1/2)TiO3-BaTiO3(BNT-BT) were prepared by the conventional piezoelectric ceramic preparation technique (free air atmosphere sintering). The influence of BaTiO3 additive amount and La2O3 additive amount on the properties of BNT-BT lead-free piezoceramics were investigated. The results show that the dielectric constant(ε) and piezoelectric strain constant(d33) of materials start increasing and then decreasing while BaTiO3 additive amount increasing, the ε and d33 of materials have maximum value (ε=1650, d33=120 PC·N-1) while x(BaTiO3)=0.06 mol. The ε and d33 of materials start increasing and then decreasing while La2O3 additive amount increasing, the ε and d33 of materials have maximum value (ε=1684, d33=153 PC·N-1) while w(La2O3)=0.3%. The influence of La2O3 additive amount on the microstructure of BNT-BT piezoelectric ceramics was analysed by SEM(scanning electron microscope). The influence mechanism of La2O3 additive amount on the properties of BNT-BT piezoelectric ceramics was discussed. The BNT-BT ceramics with optimum comprehensive properties were obtained.

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.

High-performance BiFeO_(3)eBaTiO_(3)lead-free piezoceramics insensitive to off-stoichiometry and processing temperature

It is well-known that the performance of BiFeO3eBaTiO3(BF-BT)ceramics is sensitive to composition,calcining and sintering temperature(Tcal and Tsint)due to the formation of Bi25FeO39 and/or Bi2Fe4O9 impurities and/or the volatilization of Bi_(2)O_(3).We report remarkably stable electrical properties over the range of
0.03≤x≤0.05 and 930℃≤Tsint≤970C in 0.7Bi(1þx)FeO_(3)-0.3BaTiO_(3)ceramics prepared by one-step process.This method avoids the thermodynamically unstable region of BiFeO_(3)and prevents the formation of Bi25FeO39 and/or Bi_(2)Fe_(4)O_(9)impurities even when the addition of a-Bi_(2)O_(3)raw material is intentionally deficient or rich to make off-stoichiometric BF-BT,thus greatly improving the robustness of compositional and processing.Rhombohedral-pseudocubic phase coexists in all ceramics,and their CR/CPC fraction are 48.0/52.0e50.6/49.4 and 55.9/44.1e56.6/43.4 when x increases from
0.05≤x≤0 to 0.01≤x≤0.05.The stable electrical properties of d33¼180e205 pC/N,Pr¼17.9e23.8 mC/cm^(2),and TC¼485e518℃are achieved.The maximum d_(33T)/d_(33RT)of BF-BT is twice that of soft PZT,superior to most the-state-of-art lead-free ceramics.Our results provide a synthesis strategy for designing high performance piezoelectric materials with good stability and easy industrialization.

Progress and perspective of high strain NBT-based lead-free piezoceramics and multilayer actuators

In this review,the evolution of high strain Na_(0.5)Bi_(0.5)TiO_(3)-based lead-free piezoceramics and their multilayer actuators has been explored.First,in terms of Na_(0.5)Bi_(0.5)TiO_(3)-based ceramic materials,the origin of high strain,the typical chemical modification methods of obtaining large strain and extrinsic factors affecting the large strain are discussed.Then it briefly summarizes the problems existing in Na_(0.5)Bi_(0.5)TiO_(3)-based ceramics for multilayer actuator applications.Strategies to optimize strain performance by means of microstructure control and phase structure design are also discussed.Thereafter,in terms of multilayer actuator,we describe its characteristics,applications and preparation process systematically,as well as the recent development of Na_(0.5)Bi_(0.5)TiO_(3)-based multilayer actuator.At last,perspectives on directions of following work and promising fields for the applications of the materials and their devices are presented.

Electromechanical properties of Ce-doped(Ba_(0.85)Ca_(0.15))(Zr_(0.1)Ti_(0.9))O_(3)lead-free piezoceramics

Lead-free piezoceramics based on the(Ba,Ca)(Zr,Ti)O3(BCZT) system exhibit excellent electromechanical properties for low-temperature actuation applications, but suffer from relatively high processing temperatures. Here we demonstrate an approach for the reduction of the sintering temperature and simultaneous increase of the electromechanical strain response of(Ba,Ca)(Zr,Ti)O3 piezoceramics by aliovalent doping with Ce. The samples were prepared by solid state synthesis and their crystallographic structure, dielectric, ferroelectric, and electromechanical properties were investigated. The highest d33* value of 1189 pm/V was obtained for the sample with 0.05 mol% Ce, substituted on the A-site of the perovskite lattice. The results indicate a large potential of these materials for off-resonance piezoelectric actuators.

Requirements for the transfer of lead-free piezoceramics into application

The recent review for the Restriction of Hazardous Substances Directive(RoHS)by the expert committee,appointed by the European Union,stated that the replacement of PZT“…may be scientifically and technologically practical to a certain degree…”,although replacement“…is scientifically and technically still impractical in the majority of applications.”Thus,two decades of sustained research and development may be approaching fruition,at first limited to a minority of applications.Therefore,it is of paramount importance to assess the viability of lead-free piezoceramics over a broad range of application-relevant properties.These are identified and discussed in turn:1.Cost,2.Reproducibility,3.Mechanical and Thermal Properties,4.Electrical Conductivity,and 5.Lifetime.It is suggested that the worldwide efforts into the development of lead-free piezoceramics now require a broader perspective to bring the work to the next stage of development by supporting implementation into real devices.Guidelines about pertinent research requirements into a wide range of secondary properties,measurement techniques,and salient literature are provided.

(K,Na)NbO_(3)-based lead-free piezoceramics:Phase transition,sintering and property enhancement

Most widely used piezoelectric ceramics are based on Pb(Zr,Ti)O3(PZT)composition which has adverse environmental and health effects due to its high lead content.Environmental and safety concerns with respect to the utilization,recycling,and disposal of lead-based piezoelectric ceramics have induced a new surge in developing lead-free piezoelectric ceramics.Among all the lead-free ceramics,(K,Na)NbO3(KNN)has drawn increasing attention because of its well-balanced piezoelectric properties and better environmental compatibility.On basis of the author’s work,this review summarizes the progress that has been made in recent years on development of KNN-based piezoelectric ceramics,including crystallographic structure and phase transition analysis,pressurized solid-state sintering as well as liquid-phase-assisted sintering process,and poling treatment for property enhancement.All in all,KNN is a promising lead-free system,but more research is still required both from academic and industrial interests.

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%.

Influence of CuO addition on dielectric and piezoelectric properties of(Bi_(0.5)Na_(0.5))TiO_(3)-BaTiO_(3) lead-free piezoceramics

Doping effects of CuO on the sintering behavior and electrical properties of 0.94(Bi_(0.5)Na_(0.5))TiO_(3)-0.06(BaTiO_(3))-xCuO(BNT-BT6-xCu)lead-free piezoceramic obtained by the conventional solid-state reaction method were investigated.Regarding the undoped system,it is already known that it presents the best densification values when it is sintered at 1150℃,however,the doped system was sintered at 1150℃,1100℃,1050℃,1025℃,and 975℃ to determine the effect of Cu on the densification process.Therefore,it was obtained that the CuO-doped samples sintered at 1050℃ presented the highest density values and therefore were the ones chosen to perform the characterization tests together with the undoped system.The samples were characterized using X-ray diffraction(XRD),Raman microspectroscopy,and scanning electron microscopy(SEM)analysis,whereas the ferroelectric and dielectric properties were evaluated by means of ferroelectric hysteresis loops and impedance spectroscopy studies.As a result,the addition of CuO allowed an improvement in sinterability and densification,with the subsequent grain growth,and the improvement of the piezoelectric coefficient(d_(33)).

Processing and Properties of Porous (K,Na)NbO_3-based Lead-free Piezoceramics

Porous piezoceramics are of interest for applications such as low frequency hydrophones. Porous(K,Na,Li)NbO_3-BaZrO_3-(Bi,Na)TiO_3 lead-free piezoceramics having vertical morphotropic phase boundary composition were fabricated by adding 30 μm-diameter acrylic resins. The ceramic powders were synthesized by a conventional solid-state reaction method and then mixed with the resins. Volume ratios of ceramics to resin were 90:10, 80:20, 70:30, and 60:40. After burning out the resins and binder, the specimens were sintered at 1170–1190 ℃ for 5 h. The porous specimen with 30 vol% acrylic resin had longitudinal acoustic velocity of 4518 m/s, acoustic impedance of 16.44 Mkg/(m^2·s), and hydrostatic figure of merit of 405×10^(-15)m^2/N. The hydrostatic figure of merit was about 4 times of that of monolithic ceramics. Compared with monolithic ceramics, the porous specimen had a better transducer sensitivity for underwater applications.

Large Energy Capacitive High-Entropy Lead-Free Ferroelectrics

Advanced lead-free energy storage ceramics play an indispensable role in next-generation pulse power capacitors market.Here,an ultrahigh energy storage density of~13.8 J cm^(-3)and a large efficiency of~82.4%are achieved in high-entropy lead-free relaxor ferroelectrics by increasing configuration entropy,named high-entropy strategy,realizing nearly ten times growth of energy storage density compared with low-entropy material.Evolution of energy storage performance and domain structure with increasing configuration entropy is systematically revealed for the first time.The achievement of excellent energy storage properties should be attributed to the enhanced random field,decreased nanodomain size,strong multiple local distortions,and improved breakdown field.Furthermore,the excellent frequency and fatigue stability as well as charge/discharge properties with superior thermal stability are also realized.The significantly enhanced comprehensive energy storage performance by increasing configuration entropy demonstrates that high entropy is an effective but convenient strategy to design new high-performance dielectrics,promoting the development of advanced capacitors.

Stable yellow light emission from lead-free copper halides single crystals for visible light communication

Yellow light-emitting diodes(LEDs) as soft light have attracted abundant attention in lithography room, museum and art gallery. However, the development of efficient yellow LEDs lags behind green and blue LEDs, and the available perovskites yellow LEDs suffer from the instability. Herein, a pressure-assisted cooling method is proposed to grow lead-free CsCu2I3single crystals, which possess uniform surface morphology and enhanced photoluminescence quantum yield(PLQY) stability, with only 10% PLQY losses after being stored in air after 5000 h.Then, the single crystals used for yellow LEDs without encapsulation exhibit a decent Correlated Color Temperature(CCT) of 4290 K, a Commission Internationale de l’Eclairage(CIE) coordinate of(0.38, 0.41), and an excellent 570-h operating stability under heating temperature of 100°C. Finally, the yellow LEDs facilitate the application in wireless visible light communication(VLC), which show a-3 dB bandwidth of 21.5 MHz and a high achievable data rate of 219.2 Mbps by using orthogonal frequency division multiplexing(OFDM) modulation with adaptive bit loading. The present work not only promotes the development of lead-free single crystals, but also inspires the potential of CsCu2I3in the field of yellow illumination and wireless VLC.

Research of Lead-free Na_(0.5)Bi_(0.5)TiO_(3)-BaTiO_(3)System Piezoelectric Ceramics

To reduce the coercive field of Na_(0.5)Bi_(0.5)TiO_(3),Ba TiO_(3)were added as dopant materials.Then the(1-x)Na_(0.5)Bi_(0.5)TiO_(3)-xBaTiO_(3)ceramic samples were produced in solid synthetic way.The optimum preparation condition and piezoelectric properties of the samples were investigated.The XRD results show that the fabric transites from rhombohedral to tetragonal gradually with the substitution of the Ba^(2+).The morphotropic phase boundaries(MPB)exists in the composition range of 0.06.

First Principle Study of Cesium-based Lead-free Halide Double Perovskites

Inorganic halide double perovskites A_(2)B'B"X_(6) have gained significant interests for their diverse composition,stable physicochemical properties,and potential for photoelectric applications.The influences of trivalent and monovalent cations on the formation energy,decomposition energy,electronic structure and optical properties of cesium-based lead-free Cs^(+)_(2)B'B"Br_(6) (B'=Na^(+),In^(+)Cu^(+),or Ag^(+);B"=Bi^(3),Sb^(3+),In^(3+)) are systematically studied.In view of the analysis and results of the selected double perovskites,for the double perovskites with different B-site trivalent cation,the band gap increases in the order of Cs_(2)AgInBr_(6),Cs_(2)AgSbBr_(6) and Cs_(2)AgBiBr_(6),with Cs_(2)AgBiBr_(6) possessing the highest thermodynamic stability.Therefore,the Bi-based perovskites are further studied to elucidate the effect of monovalent cation on their stability and electronics.Results show that the thermodynamic stability rises in the sequence of Cs_(2)NaBiBr_(6),Cs_(2)InBiBr_(6),Cs_(2)AgBiBr_(6) and Cs_(2)CuBiBr_(6).Notably,Cs_(2)CuBiBr_(6) exhibits a relatively narrow and appropriate band gap of 1.4634 eV,together with the highest absorption coefficient than other compounds,suggesting that Cs_(2)CuBiBr_(6) is a promising light absorbing material that can be further explored experimentally and be applied to optoelectronic devices.Our research offers theoretical backing for the potential optoelectronic application of cesium-based lead-free halide double perovskites in solar energy conversion.

Effect of Strain Rate on Tensile Behavior of Sn-9Zn-xAg-ySb;{(x, y) = (0.2, 0.6), (0.2, 0.8), (0.6, 0.2), (0.8, 0.2)} Lead-Free Solder Alloys

The tensile properties of Sn-9Zn-xAg-ySb;{(x, y) = (0.2, 0.6), (0.2, 0.8), (0.6, 0.2), (0.8, 0.2)} lead-free solders were investigated. All the test samples were annealed at 150°C for 1 hour. The tests are carried out at room temperature at the strain rate of 4.17 × 10-3 s-1, 20.85 × 10-3 s-1, and 208.5 × 10-3 s-1. It is seen that the tensile strength increases and the ductility decrease with increasing the strain rate over the investigated range. From the strain rate change test results, the strain sensitivity values are found in the range of 0.0831 to 0.1455 due to the addition of different alloying elements.

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.

Effects of Sintering Technology on PMZN Piezoceramics Properties

Pb ( Mn1/3Sb2/3 ) x ( Zn1/3Nb2/3) y ( Zr0.535 Ti0.465 ),1-x-yO3 ( PMZN) piezoelectric ceramics were fabricated, The effects of sintering temperature and heat-treatment time on properties wen discussed, the optimum preparation technology parameters were obtained. In this case, the ceramics have the highest electromechanical coupling coefficients and mechanical quality factor and the least dielectric loss. It is revealed that the PMZN piezo-ceramics material can be utilized for high-power ultrasound transducers.

Effects of phosphorus addition on the properties of Sn-9Zn lead-free solder alloy

This article explores tile effects of phosphorus addition on the wettability between Sn-9Zn solder alloy and Cu substrates, the oxidation behavior and the corrosion behavior of Sn-9Zn solder alloy. Spreading test was used to characterize the wettability of Sn-9Zn-xP solder alloys to Cu substrates. The oxidation and corrosion behaviors of Sn- 9Zn-xP solder alloys were determined by means of weight gaining, and secondary ion mass spectrometry was used to analyze the oxygen content. The role and mechanism of P in the solder alloys were also discussed. It is found that the addition of P can significantly improve the wettability of the solder alloys. Incorporating P into Sn-9Zn solder alloy obviously decreases the oxygen content and enhances the oxidation and corrosion resistance. Microstructure observations show that an appropriate amount of P can greatly refine coarse rod-like Zn-rich phases in Sn-gZn solder alloy.

Effect of diode-laser parameters on shear force of micro-joints soldered with Sn-Ag-Cu lead-free solder on Au/Ni/Cu pad

Soldering experiments with Sn-3.5Ag-0.5Cu lead-free solder on Au/Ni/Cu pad were carried out by means of diode-laser and IR reflow soldering methods respectively.The influence of different heating methods as well as output power of diode-laser on shear force of micro-joints was studied and the relationship between the shear force and microstructures of micro-joints was analyzed.The results indicate that the formation of intermetallic compound Ag3Sn is the key factor to affect the shear force and the fine eutectic network structures of micro-joints as well as the dispersion morphology of fine compound Ag3Sn,in which eutectic network band is responsible for the improvement of the shear force of micro-joints soldered with Sn-Ag-Cu lead-free solder.With the increases of output power of diode-laser,the shear force and the microstructures change obviously.The eutectic network structures of micro-joints soldered with diode-laser soldering method are more homogeneous and the grains of Ag3Sn compounds are finer in the range of near optimal output power than those soldered with IR reflow soldering method,so the shear force is also higher than that using IR reflow soldering method.When the output power value of diode-laser is about 41.0 W,the shear force exhibits the highest value that is 70% higher than that using IR reflow soldering method.

Ultrasensitive and stable X-ray detection using zero-dimensional lead-free perovskites

Sensitive and reliable X-ray detectors are essential for medical radiography,industrial inspection and security screening.Lowering the radiation dose allows reduced health risks and increased frequency and fidelity of diagnostic technologies for earlier detection of disease and its recurrence.Three-dimensional(3 D)organic-inorganic hybrid lead halide perovskites are promising for direct X-ray detection-they show improved sensitivity compared to conventional X-ray detectors.However,their high and unstable dark current,caused by ion migration and high dark carrier concentration in the 3 D hybrid perovskites,limits their performance and long-term operation stability.Here we report ultrasensitive,stable X-ray detectors made using zero-dimensional(0 D)methylammonium bismuth iodide perovskite(MA3Bi2I9)single crystals.The 0 D crystal structure leads to a high activation energy(Ea)for ion migration(0.46 e V)and is also accompanied by a low dark carrier concentration(~10^6 cm^-3).The X-ray detectors exhibit sensitivity of 10,620μC Gy-1 air cm-2,a limit of detection(Lo D)of 0.62 nG yairs-1,and stable operation even under high applied biases;no deterioration in detection performance was observed following sensing of an integrated X-ray irradiation dose of^23,800 m Gyair,equivalent to>200,000 times the dose required for a single commercial X-ray chest radiograph.Regulating the ion migration channels and decreasing the dark carrier concentration in perovskites provide routes for stable and ultrasensitive X-ray detectors.