Na0.5K0.5NbO3 and 0.9Na0.5K0.5NbO3–0.1Bi0.5Na0.5TiO3 nanocrystalline powders synthesized by low-temperature solid-state reaction

Nanocrystalline powders of K_0.5Na_0.5NbO₃ (KNN) and 0.9Na_0.5K_0.5NbO₃–0.1Bi_0.5Na_0.5TiO₃ (KNN–BNT) have been prepared using a low-temperature solid-state reaction. Phase development of the powders incurred during various calcination temperatures was examined by X-ray diffraction (XRD). Crystallite size and particle morphology of KNN powders were examined by XRD and transmission electron microscopy, respectively. Perovskite phase was formed at the temperature as low as 500 °C, and the average crystallite size of KNN powders depended on calcination temperature. In addition, the crystalline structure of KNN powders tended to change from tetragonal symmetry to orthorhombic symmetry with increase in crystallite size. Similar results were obtained in KNN–BNT system. The developed method is well suited for the mass production of niobate nanocrystalline powders due to its simplicity and low cost.     

Piezoelectric and dielectric properties of Bi0.5Na0.5TiO3–Bi0.5Li0.5TiO3 lead-free ceramics

(1 − x)Bi_0.5Na_0.5TiO₃–xBi_0.5Li_0.5TiO₃ lead-free ceramics have been prepared by a conventional solid-state reaction method, and their piezoelectric and dielectric properties have been studied. X-ray diffraction studies reveal that Li⁺ diffuses into the Bi_0.5Na_0.5TiO₃ lattices to form a solid solution with a pure perovskite structure. The addition of Bi_0.5Li_0.5TiO₃ effectively lowers the sintering temperature of the ceramics and greatly assists in the densification of the ceramics. The ceramic with x = 0.075 possesses the optimum piezoelectric properties: piezoelectric coefficient d ₃₃ = 121 pC/N and planar electromechanical coupling factor k _P = 18.3%. After the partial substitution of Li⁺ for Na⁺ in the A-sites of Bi_0.5Na_0.5TiO₃, the ceramics exhibit more relaxor characteristic, which is probably resulted from the cation disordering in the 12-fold coordination sites. The depolarization temperature T _d shifts to low temperature with the substitution level x of Li⁺ for Na⁺ increasing.     

Na0.5 Bi0.5 TiO3-K0.5 Bi0.5 TiO3系铁电体的相变研究

研究了(Na1-xKx)0.5Bi0.5TiO3体系x分别为0、0.08、0.16和0.20时陶瓷不同频率下的介电温谱,发现材料为弛豫型铁电体,材料的介电谱在室温到500℃的温度范围内存在一个介电常数-温度"台阶",一个介电常数-温度峰和一个介电损耗-温度峰,通过分析陶瓷不同温度下的电滞回线验证陶瓷在升温过程中产生了铁电-反铁电-顺电相变,采用铁电体成分起伏理论和内电场理论解释了这类弛豫型铁电体相变的原因.     

Structure and piezoelectric properties of K0.5Na0.5NbO3–Bi0.5Li0.5TiO3 lead-free ceramics

Lead-free (1−x) K_0.5Na_0.5NbO₃–xBi_0.5Li_0.5TiO₃ + 1 mol% MnO₂ piezoelectric ceramics have been prepared by a conventional ceramic technique and their structure and piezoelectric properties have been studied. Our results reveal that Bi_0.5Li_0.5TiO₃ diffuse into K_0.5Na_0.5NbO₃ lattices to form a solid solution with a perovskite structure. The addition of Bi_0.5Li_0.5TiO₃ to the K_0.5Na_0.5NbO₃ solid solution decreases the paraelectric cubic-ferroelectric tetragonal phase transition temperature (T _C) slightly, but shifts the ferroelectric tetragonal-ferroelectric orthorhombic phase transition temperature (T _O−T) significantly to low temperatures. As a result, coexistence of the orthorhombic and tetragonal phases is formed at 0.01 < x < 0.03 near room temperature, leading to a significant improvement in the piezoelectric properties of the ceramics. The ceramic with x = 0.025 exhibits a relatively high T _C (392 °C) and optimum piezoelectric properties: d ₃₃ = 191 pC/N, k _p = 51.5% and k _t = 45.5%. The ceramic also exhibit a good thermal stability of piezoelectric properties.     

(Na0.5Bi0.5)TiO3基无铅压电陶瓷研究进展

综述了（Na0.5Bi0.5)Tio3（简写为NBT）基无铅压电陶瓷的发展现状，特性及影响因素，用分子轨道理论解释了NBT强铁电性的成因，对研究较多的三个体系：NBT-ATiO3(A=Ca,Sr,Ba),NBT-BNbO3(B=Na,K)和NBT－Ln掺杂体系给予了概括介绍，内容包括成分配比，性能和应用，并提出了NBT基无铅压电陶瓷的设计原则。     

Crystallographic textured evolution in 0.85Na0.5Bi0.5TiO3–0.04BaTiO3–0.11K0.5Bi0.5TiO3 ceramics prepared by reactive-templated grain growth method

0.85Na_0.5Bi_0.5TiO₃–0.04BaTiO₃–0.11K_0.5Bi_0.5TiO₃ (BNBK) lead-free piezoelectric ceramics with extensive [001]_pc (pc: pseudo cubic) texture were fabricated by the reactive-templated grain growth method using anisotropic Bi₄Ti₃O₁₂ (BIT) particles as templates. The degree of grain orientation increased with increasing heat treatment temperature (600–1,200 °C). The obtained textured ceramics showed dense and brick-wall like microstructure, giving a Lotgering factor of 0.6. A physical understanding of interaction between BIT templates and matrix powders and the mechanism of texture evolution were proposed and confirmed by experimental evidences of X-ray diffraction patterns, scanning electron microscope images and density measurements. The piezoelectric response was enhanced by the grain orientation, and the piezoelectric constant (d₃₃) of the textured ceramics sintered at 1,170 °C attained a value of 254 pC/N, which was 41 % higher than random ceramics (180 pC/N).     

(Bi0.5Na0.5)TiO3(BNT)基无铅压电陶瓷研究进展

(Bi0.5Na0.5)TiO3(BNT)基无铅压电陶瓷体系是目前研究最广泛的功能陶瓷材料之一.综述了BNT基无铅压电陶瓷的研究现状,讨论了相关体系的设计方法、铁电性、压电性以及BNT体系的制备方法.分析比较了BNT系压电陶瓷与Pb(Zr,Ti)O3(PZT)压电陶瓷的性能差异以及存在的问题,对BNT基无铅压电陶瓷进行了展望.     

(Na0.5Bi0.5)TiO3基弛豫铁电体相变的研究进展

钛酸铋钠((Na0.5Bi0.5)TiO3,NBT)是一种典型的A位复合钙钛矿结构弛豫铁电体,具有复杂的相变序列,介电温度峰呈现明显的弛豫性.总结了NBT弛豫铁电体的相变及NBT基复合铁电体准同型相界的研究进展;从晶体结构出发,通过与B位复合型钙钛矿结构弛豫铁电体类比,对A位复合型NBT的弛豫机理进行了探讨,提出NBT弛豫性来源于其A位离子有序-无序引起的B位离子位移的变化.     

Structure and electrical properties of the Ho2O3 doped 0.82Bi0.5Na0.5TiO3–0.18Bi0.5K0.5TiO3 lead-free piezoelectric ceramics

Ho₂O₃ (0–0.7?wt%)-doped 0.82Bi_0.5Na_0.5TiO₃–0.18Bi_0.5K_0.5TiO₃ (BNKT18) lead-free piezoelectric ceramics were synthesized by a conventional solid-state reaction method. The effects of Ho₂O₃ on the microstructure and electrical properties were investigated. X-ray diffraction data shows that Ho₂O₃ in an amount of 0.1–0.7?wt% can diffuse into the lattice of the BNKT18 ceramics and form the pure perovskite phase. Scanning electron microscope (SEM) images indicate that the grain sizes of BNKT18 ceramics decrease with the increase of Ho₂O₃ content; in addition, the modified ceramics have the clear grain boundary and a uniformly distributed grain size. At room temperature, the electrical properties of the BNKT18 ceramics have been improved with the addition of Ho₂O₃, and the BNKT18 ceramics doped with 0.3wt.% Ho₂O₃ have the highest piezoelectric constant (d ₃₃?=?137?pC/N), the highest remnant polarization (P _r?=?26.9?μC/cm²), the higher relative dielectric constant (ε _r?=?980) and lower dissipation factor (tanδ?=?0.046) at a frequency of 10?kHz. The BNKT18 ceramics doped with 0.1?wt% Ho₂O₃ have the highest planar coupling factor (k _p?=?0.2426).     

(Na0.5Bi0.5)TiO3-BaTiO3的合成与压电性能

合成了具有单一钙钛矿结构的(Nao.5Bi0.5)1-xBaxTiO3超细粉料,研究其陶瓷的压电性能.结果表明,柠檬酸与金属离子的摩尔比(C/Mn )和前驱体溶液的pH值是影响溶胶与凝胶形成的主要因素,凝胶在600℃下热处理1 h后可形成单一钙钛矿结构的(Nao.5Bi0.5)1-xBaxTiO3超细粉料.用柠檬酸盐法合成粉料的颗粒细小、化学成分均匀,有利于提高(Na0 5Bi0.5)1-xBaxTiO3陶瓷的压电性能.在准同质相界附近的组分存在较多的自发极化取向,因而表现出优良的压电性能.x=0.06时,柠檬酸盐法制备陶瓷样品的压电常数d33达到180 pC/N.     

水热法制备K0.5 Bi0.5 TiO3纳米粉体

以Bi(NO3)3·5H2O、Ti(OC4H9)4、KOH为原料,研究和分析了水热条件下纳米K0.5Bi0.5TiO3(KBT)粉体和影响KBT晶体生长与形成的各个影响因素,并利用XRD、TEM、ED等分析方法对所得粉体的晶相、微观形貌、分散性等性质进行了表征.结果表明,反应温度为180℃,保温时间为24h,KOH浓度为4～12mol/L时能制备出纯净的、结晶完整、分散性良好、钙钛矿型的纳米K0.5Bi0.5TiO3晶体,其颗粒尺寸为15～75nm.     

Origin of the large strain response in tenary SrTi0.8Zr0.2O3 modified Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3 lead-free piezoceramics

The perovskite oxides (1 ? x)Bi_0.5(Na_0.9K_0.1)_0.5TiO₃–xSrTi_0.8Zr_0.2O₃ (SZT1000x, x = 0, 0.2, 0.4, 0.6, 0.8, and 1 %) were prepared via the conventional solid-state reaction method. The room temperature ferroelectric P–E loops coordinate with polarization current density J–E curves illustrated the changes of ferroelectric domains and polar nanoregions under different driving fields exhaustively. The composition and electric field dependent strain behavior of this system were investigated to develop a lead-free piezoelectric material with a large strain response at a lower electric field. A large strain of 0.44 % (S _max/E _max = 744 pm/V) at an applied field of 50 kV/cm was obtained at the composition of 0.6 mol% SZT. Temperature-dependent hysteresis measurements reveal the primary origin of the large strain is due to the presence of a nonpolar phase at a zero field. Upon the application of an electric field, the nonpolar phase that can easily transform into a long-range ferroelectric phase, and then brings the system back to its unpoled state once the applied electric field is removed. Notably, the electric field required to deliver large strains is reduced to 40 kV/cm while the S _max/E _max reached up to 717 pm/V, indicating that the developed material is highly promising for actuator applications.     

Ferroelectric and piezoelectric properties of (1 − x) (Bi0.5Na0.5)TiO3–xBaTiO3 ceramics

Lead-free ceramics based on bismuth sodium titanate (Bi_0.5Na_0.5TiO₃, BNT)–barium titanate (BaTiO₃,BT) have been prepared by solid state reaction process. The (1?x)BNT–(x)BT (x = 0.01,0.03,0.05,0.07) ceramics were sintered at 1,150 °C for 4 h in air, show a pure perovskite structure. X-ray diffraction analysis indicates that a solid solution is formed in (1?x)BNT–(x)BT ceramics with presence of a morphotropic phase boundary (MPB) between rhombohedral and tetragonal at x = 0.07. Raman spectroscopy shows the splitting of (TO₃) mode at x = 0.07 confirming the presence of MPB region. The temperature dependence dielectric study shows a diffuse phase transition with gradual decrease in phase transition temperature (T_m). The dielectric constant and diffusivity increases with increase in BT content and is maximum at the MPB region. With the increase in BT content the maximum breakdown field increases, accordingly the coercive field (E_c) and remnant polarization (P_r) increases. The piezoelectric constant of (1 ? x)BNT–(x)BT ceramics increases with increase in BT content and maximum at x = 0.07, which is the MPB region. The BNT–BT system is expected to be a new and promising candidate for lead-free dielectric and piezoelectric material.     

(Na,K)0.5Bi0.5TiO3无铅压电陶瓷的结构与性能研究

研究了K0.5Bi0.5TiO3(KBT)含量对Na0.5Bi0.5TiO3-K0.5Bi0.5TiO3(BNKT)无铅压电陶瓷的显微组织结构及压电性能的影响规律,结果表明随KBT含量增加,BNKT无铅压电陶瓷的晶胞参数增大,密度减小,晶粒尺寸减小,居里温度从326℃升高到360℃,压电常数、介电常数和介电损耗增加,机械品质因数下降;KBT含量为0.15mol的(Na0.85K0.15)0.5Bi0.5TiO3无铅压电陶瓷位于准同型相界处,具有较佳的压电性能.     

Na0.5Bi0.5TiO3-K0.5Bi0.5TiO3无铅压电陶瓷的制备与性能

采用传统的干压成型法制备了Na0.5Bi0.5TiO3-K0.5Bi0.5TiO3无铅压电陶瓷,研究了不同K0.5Bi0.5TiO3含量对Na0.5Bi0.5TiO3-K0.5Bi0.5TiO3陶瓷的微观结构与电性能的影响规律.结果表明,Na0.5Bi0.5TiO3-K0.5Bi0.5TiO3无铅压电陶瓷随K0.5Bi0.5TiO3含量增加,晶格常数增大,密度减小,晶粒尺寸减小,压电常数先增大后减小,介电常数增大,介电损耗增加,机械品质因数下降,而居里温度不断升高,在200℃附近存在由铁电相向反铁电相转变的一个相变点,组分为0.84 Na0.5Bi0.5TiO3-0.16 K0.5Bi0.5TiO3的陶瓷位于准同型相界附近,具有最佳的压电性能.     

Energy storage properties of (1 − x)(Bi0.5Na0.5)TiO3–xKNbO3 lead-free ceramics

In this study, a simple compound (1 ? x)(Bi_0.5Na_0.5)TiO₃–xKNbO₃ (x = 0 – 0.12) lead-free bulk ceramic was developed for high electric power pulse energy storage applications. The dielectric and ferroelectric properties of the ceramics were measured. The results illustrate that the energy storage density of the ceramics is enhanced by the addition of KNbO₃. The influence of applied electric field, temperature, and fatigue on the energy storage properties of the ceramics was evaluated for the composition-optimized (Bi_0.5Na_0.5)TiO₃–0.1KNbO₃ ceramic. The results demonstrate that (Bi_0.5Na_0.5)TiO₃–0.1KNbO₃ ceramic is a promising lead-free material for high power pulse capacitor applications. The excellent energy storage properties of the (Bi_0.5Na_0.5)TiO₃–0.1KNbO₃ ceramics are ascribed to the reversible relaxor–ferroelectric phase transition induced by the electric field.     

(Bi0.5Na0.5)TiO3系无铅压电陶瓷研究现状与展望

BNT陶瓷由于具有良好的压电性、高居里温度和烧结过程中无毒、易控制性等优点而倍受青睐.本文介绍了无铅压电陶瓷的研究概况、相变过程及其基本性质、制备工艺,根据已有的研究经验着重对BNT陶瓷掺杂改性进行了探讨,并展望了它的发展前景.     

Improved electrical and ferroelectric properties of multiferroic Na0.5Bi0.5TiO3/Bi1.07Nd0.03FeO3/Na0.5Bi0.5TiO3 sandwiched structure by a sol–gel process

A ferroelectric/multiferroic/ferroelectric sandwiched structure composed by Na_0.5Bi_0.5TiO₃ (NBT) and Bi_1.07Nd_0.03FeO₃ (BNF) with a LaNiO₃ buffer layer were prepared by a sol–gel method. X-ray diffraction indicated the NBT/BNF/NBT films exhibited a pure perovskite structure. The average grain size of BNF and NBT/BNF/NBT were found to be 40 and 80 nm, respectively. Interestingly, the electrical and ferroelectric properties such as leakage current, dielectric constant, and remnant polarization of NBT/BNF/NBT sandwiched layer, were superior to those of BNF single film. However, the saturation magnetization of NBT/BNF/NBT sandwiched layer was reduced. Our work suggested the NBT/BNF/NBT sandwiched layer with improved multiferroic characteristics have a promising application for future information storage devices.