Effects of Li Substitution and Sintering Temperature on Properties of Bi0.5（Na,K）0.5TiO3 Lead-Free Piezoelectric Ceramics

Bi0.5 （Na0.72K0.28- x Lix ）0.5 TiO3 （BNKLT- 100x） lead-free piezoelectric ceramics are synthesized by conventional solid state sintering techniques. The dielectric and piezoelectric properties of the BNKLT-100x ceramics as a function of Li content are systematically investigated. It is found that not only Li content but also the sintering temperature has a strong effect on the piezoelectric properties of BNKLT. The piezoelectric constant d33 Of BNKLT varies from 120 to 252pC/N in the Li content range from 0.03 to 0.16. In the sintering temperature range from 1080 to 1130℃, the d33 value of BNKLT-6 changes from 200pC/N to 252pC/N. The BNKLT-6 sample sintered at 1100℃ has the highest piezoelectric constant d33 of 252pC/N, with the electromechanical coupling factors kp of 0.32 and kt of 0.44.     

Piezoelectricity in K_(1-x)Na_xNbO_3: First-principles calculation

The piezoelectric properties of K1-xNaxNbO3 are studied by using first-principles calculations within virtual crystal approximation. To understand the critical factors for the high piezoelectric response in K1-x Na x Nb O3, the total energy,piezoelectric coefficient, elastic property, density of state, Born effective charge, and energy barrier on polarization rotation paths are systematically investigated. The morphotropic phase boundary in K1-x Na x Nb O3 is predicted to occur at x = 0.521, which is in good agreement with the available experimental data. At the morphotropic phase boundary, the longitudinal piezoelectric coefficient d33 of orthorhombic K0.5Na0.5NbO3 reaches a maximum value. The rotated maximum of d*33is found to be along the 50° direction away from the spontaneous polarization(close to the [001] direction). The moderate bulk and shear modulus are conducive to improving the piezoelectric response. By analyzing the energy barrier on polarization rotation paths, it is found that the polarization rotation of orthorhombic K0.5Na0.5NbO3 becomes easier compared with orthorhombic KNbO3, which proves that the high piezoelectric response is attributed to the flattening of the free energy at compositions close to the morphotropic phase boundary.     

The low-temperature sintering and microwave dielectric properties of （Zno.7Mgo.3） TiO3 ceramics with H3BO3

The effects of the addition of H3BO3 on the microstructure, phase formation, and microwave dielectric properties of （Zn0.TMg0.3）TiO3 ceramics sintered at temperatures ranging from 890 ℃ to 950 ℃ are investigated. H3BO3 as a sintering agent can effectively lower the sintering temperature of ZMT ceramics below 950 ℃due to the liquid-phase effect. The microwave dielectric properties are found to strongly correlate with the amount of H3BO3. With the increase in H3BO3 content, the dielectric constant （er） monotonically increases, but the quality factor （Q x f） reaches a maximum at 1 wt% H3BO3, and the apparent density of ZMT ceramics with H3BO3〉 1 wt% gradually decreases. At 950 ℃, the ZMT ceramics with 1% H3BO3 exhibit excellent microwave dielectric properties： er = 19.8, and Q x f -- 43800 GHz （8.94 GHz）.     

Relaxor Behaviour and Ferroelectric Properties of （Li0.12Na0.88） （Nb0.9-xWa0.10Sbx）O3 Lead-Free Ceramics

New lead-free ceramics （Lio.12Na0.88） （Nbo.9-x Ta0.10 Sbx） 03 （0.01 × 0.06） are synthesized by solid-state reaction method. The dielectric, piezoelectric and ferroelectric properties of the ceramics are studied. The dielectric constant dependence with temperature and frequency of the ceramic specimen with x = 0.04 shows typical characteristics of relaxor ferroelectrics, and the Vogel-Fulcher relationship is fulfilled. The dielectric behaviour and its relation to the phase transition phenomena are discussed. The polarization hysteresis loops at room temperature are also measured.     

Thermal Stability and Humidity Resistance of ScTaO4 Modified （K0.5Na0.5）NbO3 Ceramics

Lead-free （Na0.5K0.5）NbO3-xmol% ScTaO4 （x=0-1.5） ceramics are prepared using the conventional solid-state reaction method and their properties are investigated in detail. The results indicate that the piezoelectric properties and density are improved by the introduction of ScTaO4. Due to the high orthorhombic-tetragonal phase transition temperature TO-T （around 200°C）, stable piezoelectric properties against temperature are obtained. In a wide temperature range of 15-160°C, kp of the （Na0.5K0.5）NbO3-0.5mol% ScTaO4 ceramic remains almost unchanged and d31 increases slightly from 59pC/N to 71pC/N. The deliquescent problem is effectively solved by the addition of ScTaO4. The piezoelectric properties of ScTaO4 modified （Na0.5K0.5）NbO3 ceramics show no obvious reduction and dielectric loss increases slightly after 120h of immersion. From the analysis, it is suggested that the density is an important factor that improves the humidity resistance of the specimens.     

The low-temperature sintering and microwave dielectric properties of (Zn_(0.7)Mg_(0.3))TiO_3 ceramics with H_3BO_3

The effects of the addition of H 3 BO 3 on the microstructure, phase formation, and microwave dielectric properties of (Zn 0.7 Mg 0.3 )TiO 3 ceramics sintered at temperatures ranging from 890 ℃ to 950 ℃ are investigated. H 3 BO 3 as a sintering agent can effectively lower the sintering temperature of ZMT ceramics below 950 ℃ due to the liquid-phase effect. The microwave dielectric properties are found to strongly correlate with the amount of H 3 BO 3 . With the increase in H 3 BO 3 content, the dielectric constant (ε r ) monotonically increases, but the quality factor (Q × f ) reaches a maximum at 1 wt% H 3 BO 3 , and the apparent density of ZMT ceramics with H 3 BO 3 ≥ 1 wt% gradually decreases. At 950 ℃, the ZMT ceramics with 1% H 3 BO 3 exhibit excellent microwave dielectric properties: ε r = 19.8, and Q × f = 43800 GHz (8.94 GHz).     

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(K0.5Na0.5Nb O3;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 morphology are characterized respectively by x-ray diffraction and scanning electron microscopy.This new material has a much higher piezoelectric coefficient(163 p C·N-1) than traditional piezoelectric ceramics(131 p C·N-1).On this basis therefore,a strategy for the future study and development of lead-free KNN-based piezoelectric glass ceramics is proposed.     

Mechanical Reinforcement and Piezoelectric Properties of PZT Ceramics Embedded with Nano-Crystalline

The double-scale lead zirconate titanate （PZT） piezoelectric ceramics were prepared by the solid state processing with PZT nano-crystalline and micro-powder. The microstructures, electrical and mechanical properties of the double-scale PZT are investigated. All the sintered ceramics exhibit a single perovskite structure and the grain size of the dou ble-scale PZT reduces due to the incorporation of PZT nano-crystalline. Compared to normal PZT, the mechanical properties increase significantly and the piezoelectric properties decrease slightly. Mechanisms responsible for the reinforcement of the double-scale PZT are discussed.     

Influences of spark plasma sintering temperature on the microstructures and thermoelectric properties of(Sr_(0.95)Gd_(0.05))TiO_3 ceramics

(Sr0.95Gd0.05)Ti O3(SGTO) ceramics are successfully prepared via spark plasma sintering(SPS) respectively at 1548,1648,and 1748 K by using submicron-sized SGTO powders synthesized from a sol–gel method.The densities,microstructures,and thermoelectric properties of the SGTO ceramics are studied.Though the Seebeck coefficient shows no obvious difference in the case that SPS temperatures range from 1548 K to 1648 K,the electrical conductivity and the thermal conductivity increase remarkably due to the increase in grain size and density.The sample has a density higher than 98%theoretical density as the sintering temperature increases up to 1648 K and shows average grain sizes increasing from～ 0.7 μm to 7 μm until 1748 K.As a result,the maximum of the dimensionless figure of merit of ～ 0.24 is achieved at～ 1000 K for the samples sintered at 1648 K and 1748 K,which was ～ 71% larger than that(0.14 at ～ 1000 K) for the sample sintered at 1548 K due to the enhancement of the power factor.     

KNN Based Lead-Free Piezoceramics with Improved Thermal Stability

Lead-free piezoelectric ceramics （1 - x） （Na0.53K0.404 Li0.066）Nb0.92 Sb0.08 03 ＋xZrTiO3 are fabricated by conventional solid-state sintering method, and their dielectric and piezoelectric characteristics are investigated. With the addition of SrTiO3, the growth of the grain size is restrained, meanwhile the phase transition temperature of orthorhombic-tetragonal is shifted below room temperature. It is found that the ceramics with x = 0.010 exhibit excellent piezoelectric properties （d33 = 220 pC/N, kp = 41%, kt = 39%） and improved thermal stability around room temperature. The results indicate that these materials are promising lead-free piezoceramics for practical operations.     

A位等价与非等价取代对(K0.5Na0.5)NbO3陶瓷极化的影响

研究了在铌酸钾钠基陶瓷中,A位等价与非等价取代对陶瓷极化温度和极化电场的影响,结果表明:A位等价取代的陶瓷对极化温度和极化电场没有强烈依赖性,可以使极化足够充分,能有效提高铌酸钾钠基陶瓷的压电性能;相反,A位非等价取代的陶瓷对极化温度和极化电场敏感,容易击穿,极化不充分,限制了铌酸钾钠基陶瓷的压电性能. 关键词： 铌酸钾钠 极化 压电     

Properties of non-stoichiometric 0.935(K0.5+xNa0.5+x)NbO3-0.065LiSbO3 lead-free piezoelectric ceramics

0.935(K_0.5+xNa_0.5+x)NbO₃-0.065LiSbO₃ lead-free piezoelectric ceramics were prepared by normal sintering, and their piezoelectric and dielectric properties were investigated by varying the compensating amount x of alkaline elements (Na and K) addition. It was found that the crystal structure changed from tetragonal to orthorhombic with increasing x from −0.010 to 0.010. An MPB was tailored by optimizing the alkaline elements contents. Enhanced electrical and electromechanical responses of d₃₃=253 pC/N, k_p=0.47, k_t=0.45 and tanδ=0.027 were obtained in the ceramics with x=0.005. These excellent piezoelectric and electromechanical properties indicate that this system may be an attractive lead-free material for a wide range of electro-mechanical transducer applications.     

Dielectric and piezoelectric properties of non-stoichiometric (K0.5Na0.5)(Nb0.9+xTa0.1)O3 ceramics

In the study, in order to develop the lead-free piezoelectric ceramics for actuator, transformer and other electronic-devices application, (K_0.5Na_0.5)(Nb_0.9+xTa_0.1)O₃ + 0.5 mol% CuO + 0.2 mol% MnO₂ ceramics were prepared by conventional mixed oxide method. The effects of B-site non-stoichiometry in [(K_0.5Na_0.5)] [(Nb_0.9+xTa_0.1)O₃] ceramics on microstructure and piezoelectric properties were investigated. The density, electromechanical coupling factor (k_p), mechanical quality factor (Q_m), piezoelectric constant (d₃₃), T_C and T_O-T of NKNT ceramics with x = 0.0065 showed the optimum values of 4.58 g/cm³, 0.427, 1554, 109 pC/N, 373 °C and 226 °C, respectively, suitable for piezoelectric motor, and transformer applications.     

K0.5Na0.5NbO3-LiSbO3-BiFeO3/CuFe2O4复合陶瓷的制备与磁电性能研究

采用传统的固相法制备了(1-x)(K_0.5Na_0.5NbO₃-LiSbO₃-BiFeO₃)-xCuFe₂O₄ (x=0.1, 0.2, 0.3, 0.4) 磁电复合陶瓷, 并借助X射线衍射仪、扫描电镜和磁电耦合系数测试仪等对复合陶瓷的微结构和性能进行了分析. 结果表明, 复合陶瓷的K_0.5Na_0.5NbO₃-LiSbO₃-BiFeO₃和CuFe₂O₄物相之间发生了一定的离子相互扩散作用, 且两相的颗粒大小匹配性较好. 随着CuFe₂O₄含量增加, 复合陶瓷的压电系数从130 pC/N减小到30 pC/N, 饱和磁致伸缩系数从4.5×10^-6增加到12.4×10^-6左右, 磁电耦合系数表现出先增加后减小, 在x=0.3时获得最大的磁电耦合系数9.4 mV·cm^-1·Oe^-1. 关键词： 0.5Na_0.5NbO₃-LiSbO₃-BiFeO₃')" href="#">K_0.5Na_0.5NbO₃-LiSbO₃-BiFeO₃ 2O₄')" href="#">CuFe₂O₄ 磁电耦合     

Structure, ferroelectric and piezoelectric properties of (Bi1−x−yNa0.925−x−yLi0.075)0.5BaxSryTiO3 lead-free piezoelectric ceramics

Lead-free multi-component ceramics (Bi_1−x−yNa_{0.925−x−y}Li_0.075)_0.5Ba_xSr_yTiO₃ have been prepared by an ordinary sintering technique and their structure and electrical properties have been studied. All the ceramics can be well-sintered at 1100 °C. X-ray diffraction patterns shows that Li⁺, Ba²⁺ and Sr²⁺ diffuse into the Bi_0.5Na_0.5TiO₃ lattices to form a new solid solution with a pure perovskite structure, and a morphotropic phase boundary (MPB) is formed at 0.04 < x < 0.08. As compared to pure Bi_0.5Na_0.5TiO₃ ceramic, the coercive field E_C of the ceramics decreases greatly and the remanent polarization P_r of the ceramics increases significantly after the formation of the multi-component solid solution. Due to the MPB, lower E_C and higher P_r, the piezoelectricity of the ceramics is greatly improved. For the ceramics with the compositions near the MPB (x = 0.04–0.08 and y = 0.02–0.04), piezoelectric coefficient d₃₃ = 133–193 pC/N and planar electromechanical coupling factor k_P = 16.2–32.1%. The depolarization temperature T_d reaches a minimum value near the MPB. The temperature dependences of the ferroelectric and dielectric properties suggest that the ceramics may contain both the polar and non-polar regions at temperatures near/above T_d.     

Relationship between phase structure and electrical properties of (K0.5Na0.5)NbO3-LiTaO3 lead-free ceramics

Lead-free piezoelectric ceramics of (1−x)K_0.5Na_0.5NbO₃-xLiTaO₃ (KNN-LT) system have been investigated in this work. X-ray diffraction, Raman spectra measurements, DSC (Differential Scanning Calorimetric), and dielectric constant versus temperature provide direct evidence that the phase transition temperature between tetragonal and orthorhombic shift to lower temperature with the increasing of LT content. The KNN-0.05LT ceramics exhibit the highest high-field d₃₃ up to 220 pm/V. At the same time, we also investigated the relationship between phase structure and electric properties, showing that the orthorhombic phase presents better piezoelectric temperature stabilities than the tetragonal phase. The result may provide a new way for KNN-based lead-free ceramics.     

Characterization of lead free (K0.5Na0.5)NbO3-LiSbO3 piezoceramic

(K_0.5Na_0.5)NbO₃ (KNN) based lead free ceramics have been fabricated by a solid state reaction. In this work, LiSbO₃ (LS) modified KNN based ceramics were sintered at atmospheric pressure and high density (>96% theoretical) was obtained. The detailed elastic, dielectric, piezoelectric and electromechanical properties were characterized by using the resonance technique combined with the ultrasonic method. The full set of material constants for the obtained polycrystalline ceramics were determined and compared to the pure hot pressed KNN counterpart. KNN-LS polycrystalline ceramic was found to have higher elastic compliance, dielectric permittivity and piezoelectric strain coefficients, but lower mechanical quality factor, when compared to pure KNN, exhibiting a “softening” behavior. However, a high coercive field (∼17 kV/cm) was found for the LS modified KNN material. The properties as a function of temperature were determined in the range of −50-250 ^°C, showing a polymorphic phase transition near room temperature, giving rise to improved piezoelectric behavior.     

Structural and electrical properties of (Na0.85K0.15)0.5Bi0.5TiO3 thin films deposited on LaNiO3 and Pt bottom electrodes

(Na_0.85K_0.15)_0.5Bi_0.5TiO₃ thin films were deposited on LaNiO₃(LNO)/SiO₂/Si(1 0 0) and Pt/Ti/SiO₂/Si(1 0 0) substrates by metal-organic decomposition, and the effects of bottom electrodes LNO and Pt on the ferroelectric, dielectric and piezoelectric properties were investigated by ferroelectric tester, impedance analyzer and scanning probe microscopy, respectively. For the thin films deposited on LNO and Pt electrodes, the remnant polarization 2P_r are about 22.6 and 8.8 μC/cm² under 375 kV/cm, the dielectric constants 238 and 579 at 10 kHz, the dielectric losses 0.06 and 0.30 at 10 kHz, the statistic d_33eff values 95 and 81 pm/V. The improved piezoelectric properties could make (Na_1−xK_x)_0.5Bi_0.5TiO₃ thin film as a promising candidate for piezoelectric thin film devices.     

Na0.25K0.25Bi0.5TiO3无铅压电陶瓷的介电特性研究

用固相反应法制备了Na_0.25K_0.25Bi_0.5TiO₃ (NKBT50)陶瓷，研究了该陶瓷在室温至400℃温度范围内的介电性能.发现该陶瓷的介电温谱与烧结气氛、极化状态有关.在空气中烧结的未极化样品在70℃附近存在介电和损耗峰，而极化后及在氧气氛中烧结的样品并不存在该介电、损耗峰.分析认为70℃的介电和损耗峰与氧空位形成的缺陷偶极子的极化弛豫有关.热激电流显示，陶瓷的去极化温度为225℃，与此相对应的介电、损耗峰也 关键词： 介电性能 氧空位 极化弛豫 钛酸铋钠钾     

Microstructure and piezoelectric properties of Bi0.5(Na0.82K0.18)0.5TiO3−NaSbO3 ceramics

Lead-free piezoelectric ceramics (1−x)Bi_0.5(Na_0.82K_0.18)_0.5TiO₃−xNaSbO₃ have been prepared by a conventional ceramics technique, and their microstructure and electrical properties have been investigated. The addition of NaSbO₃ has no remarkable effect on the crystal structure within the studied doping content; however, an obvious change in microstructure took place. With increase in NaSbO₃ content, the temperature from a ferroelectric to antiferroelectric phase transition increases, and the temperature for a transition from antiferroelectric phases to paraelectric phases changes insignificantly. Simultaneously, the temperature range between the rhombohedral phase transition point and the Curie temperature point becomes smaller. The piezoelectric properties significantly increase with increase in NaSbO₃ content and the piezoelectric constant and electromechanical coupling factor attain maximum values of d₃₃=160 pC/N and k_p=0.333 at x=0.01. The results indicate that (1−x)Bi_0.5(Na_0.82K_0.18)_0.5TiO₃−xNaSbO₃ ceramic is a promising lead-free piezoelectric candidate material.