(Na1-xKx0.5)Bi0.5TiO3-xSrTiO3-0.3Mn陶瓷的性能研究

采用固相法制备了(Na1-x Kx)0.5Bi0.5TiO3-xSrnO3-0.3Mn系无铅压电陶瓷,研究了该系统的压电性能.XRD分析表明所得陶瓷样品在室温下均为三方、四方共存的钙钛矿结构,随着sr的增加三方相减少四方相增加.该体系样品具有优异的压电性能,在sr含量为0.02时,压电常数d33、平面机电耦合系数kp和厚度机电耦合系数Kt同时达到最大值,分别为171pC·N-1、33.1%和30.5%,sr具有"软性"添加物的作用.     

Na0.5Bi0.5TiO3-Ba0.5Sr0.5Nb2O6无铅压电陶瓷的研究

采用固相法制备了(1-x)(Na0.5Bi0.5)TiO3-xBa0.5Sr0.5Nb2O6(0≤x≤1.0％)(简称(1-x)NBT-xBSN)无铅压电陶瓷,研究了不同BSN含量(x=0,0.1％,0.3％,0.5％,0.7％,1.0％,摩尔分数)样品的物相组成、显微结构及电性能.结果表明:所有样品均为纯钙钛矿结构,随掺杂量x的增加,陶瓷的相对密度pr、压电常数d33和机电耦合系数kp均先增大后降低,机械品质因子Qm和退极化温度Td则逐渐下降.该体系陶瓷具有弥散相变特征,弥散指数介于1.6～1.7.当x=0.5％时,陶瓷获得最佳性能:d33=92pC/N,kp=0.164,Qm=89,εr=650,tanδ=5.47％,pr=96.5％.     

铜掺杂对(Na0.5K0.5)NbO3无铅压电陶瓷性能的影响

采用传统固相反应法对(Na0.5K0.5)NbO3压电陶瓷进行铜掺杂改性研究。使用SEM、XRD并结合常规压电陶瓷性能测试手段对该体系的显微结构、压电性能等进行表征。研究结果表明:CuO的掺入使材料出现“硬化”现象,即材料的压电系数d33、平面机电耦合系数Kp和介电损耗tanδ下降了,机械品质因子Qm大大提高;CuO掺入量在1%mol时各项性能最佳。另外,从SEM图片中可以看出:(Na0.5K0.5)NbO3压电陶瓷材料的平均晶粒尺寸随着CuO掺入量的增加明显变大。这表明CuO有烧结助熔作用,能降低烧成温度。     

准同型相界附近(Na1-xKx)0.5Bi0.5TiO3的制备及性能研究

利用固相法制备了（Na1-xKx）0.5Bi0.5TiO3系压电陶瓷，XRD分析表明所得陶瓷样品为纯的钙钛矿结构，其准同型相界在x=0．18～0．22之间；电子探针显微分析显示所做陶瓷样品晶粒发育良好，具有规则的外形和明显的晶界；实验所得陶瓷样品损耗tanδ最大不超过5％，最好的压电常数d33=153 pC／N，平面机电耦合系数kp=0．299，它们分别出现在x=0．22和0．20处。     

(K_(0.5)Na_(0.5))NbO_3-CaZrO_3基无铅压电陶瓷的相结构和压电性能研究

采用传统陶瓷工艺制备了(1-x)(K0.5Na0.5)NbO3-xCaZrO3(简称KNN-CZ)无铅压电陶瓷。分析了陶瓷样品的相结构组成。测试结果表明:所有陶瓷样品均为钙钛矿相,未发现其它晶相。随着CaZrO3含量的增加,(1-x)KNNxCZ陶瓷的相结构由正交相转变为四方相,最后变为立方相。研究了不同CaZrO3含量对压电性能的影响,实验表明:当CaZrO3含量为0.05mol时,压电常数d33和径向机电耦合系数kp分别达到了最大值196pC/N和0.35。(1-x)KNNxCZ(x=0.05)陶瓷的压电性能展现了良好的温度稳定性和经时稳定性,这些结果表明(1-x)KNN-xCZ(x=0.05)陶瓷是一种优良的无铅压电备选材料。     

CeO2、Sb2O3掺杂(Na0.88K0.12)0.5Bi0.5TiO3无铅陶瓷的压电性能研究

采用传统陶瓷的制备方法制备了CeO2(0～1.0wt%)和Sb2O3(0～0.6wt%)掺杂的(Na0.88K0.12)0.5Bi0.5TiO3无铅压电陶瓷。运用XRD技术研究了样品的晶体结构,测试并分析了样品的介电、压电性能以及谐振频率温度系数。结果表明:所有组成均呈三方结构的钙钛矿型固溶体特征。在适当掺杂剂用量范围内,压电陶瓷的压电常数、介电常数和介电损耗升高,而平面机电耦合系数降低。CeO2和Sb2O3掺杂均改善了(Na0.88K0.12)0.5Bi0.5TiO3压电陶瓷频率温度稳定性。     

Na0.5Bi0.5TiO3–K0.5Bi0.5TiO3–BaTiO3–SrTiO3陶瓷的准同型相界与电性能

采用固相法制备了 Na0.5Bi0.5TiO3–K0.5Bi0.5TiO3–BaTiO3–SrTiO3（NBT–KBT–BT–ST）陶瓷,该体系是按（1–2x）（0.8NBT–0.2KBT）–x（0.94NBT–0.06BT）–x（0.74NBT–0.26ST） （x = 0.10、0.20、0.25、0.30、0.35、0.40、0.45）组合而成的,研究了该系陶瓷的结构与电性能。结果表明：所有样品都处于三方–四方准同型相界区域。该系陶瓷在准同型相界附近表现出了优异的压电性能,压电常数 d33、机电耦合系数 kp和剩余极化强度 Pr随 x 的增加先升高后降低,其中 x=0.35 陶瓷的电性能最佳：d33= 210 pC/N,kp= 0.319,Pr= 39.3 μC/cm2,Ec= 20.2 kV/cm,是一种良好的无铅压电陶瓷候选材料。依据准同型相界组成的线性组合规律来寻找具有优异压电性能的 NBT–KBT–BT–ST 陶瓷准同型相界组成是可行的。     

Pb(Mg1/3Nb2/3)O3-PbZrO3-PbTiO3压电陶瓷的电学性能研究

采用固相烧结法制备了0.40Pb(Mg1/3Nb2/3)O3-(0.6-x)PbZrO3-xPbTiO3压电陶瓷,系统研究了其组分变化对晶体结构、介电和压电性能的影响。研究结果表明,所有样品均属于钙钛矿结构,无第二相产生。随着组分的变化,存在三方相向四方相的转变,并且在x = 0.38附近获得准同型相界组分,呈现出最优的电学性能,最高的压电系数d33 = 520 pC/N,居里温度TC = 238 °C,平面机电耦合系数kp = 0.60,厚度机电耦合系数kt = 0.52,纵向机电耦合系数k33 = 0.73。     

(Na1-xKx)0.5Bi0.5TiO3系无铅压电陶瓷的电学性能研究

利用固相法制备了(Na1-xKx)0.5Bi0.5TiO3系压电陶瓷,所得陶瓷样品介电损耗tanδ最大不超过5%,最好的压电常数d33=153pC/N,平面机电耦合系数kp=0.299,它们分别出现在x=0.22和0.20处。同时通过对其介电性能的测试,表明该样品具有弛豫铁电性,是典型的弛豫铁电体。     

Na_(0.5)Bi_(0.5)TiO_3-K_(0.5)Bi_(0.5)TiO_3系富钠区陶瓷固溶体的电物理性能研究

本工作对xNa_(0.5)Bi_(0.5)TiO_3-(1-x)K_(0.5)Bi_(0.5)TiO_3系(0.73≤x≤0.95)陶瓷固溶体的压电、铁电性质进行了研究。发现准同型相界位于x=0.81处;在相界,压电参数出现极值。在该系统中,获得了高厚度机电耦合系数、高频率常数、低平面机电耦合系数、低相对介电常数的超声换能器材料。该材料还具有无公害,不需密封烧结等工艺优点。     

（1-x）NBT—xBaTiO3系陶瓷材料的制备和表征

对（1-x）NBT—xBaTiO3在x≤0．30范围内选取不同的X值,采用固相合成法制备样品。通过XRD和SEM等分析测试手段,分析了不同掺量的BaTiO3对材料微观结构和晶粒状况的影响,确定了材料的三方、四方准同型相界组成范围。结果表明,随着Ba^2＋取代量的增加,样品晶体结构逐渐由三方相向四方相转变,在x=0．06～0．10组成范围内存在三方、四方相共存的准同型相界;Ba^2＋的掺入抑制了晶粒的长大,使晶粒的尺寸变小。     

Actuation mechanisms in mixed-phase K0.5Bi0.5TiO3-BiFeO3-PbTiO3 ceramics

We report an in-situ synchrotron X-ray diffraction study of K_0.5Bi_0.5TiO₃-BiFeO₃-PbTiO₃ ceramics, which exhibit a T_c of around 450 °C. The electromechanical actuation mechanisms comprise contributions from coexisting tetragonal and rhombohedral phases. The tetragonal {200} grain family exhibited the highest effective lattice strain, up to 8.2 × 10⁻³ at 5 kV/mm. Strong strain anisotropy in the tetragonal phase and field-induced intergranular stresses facilitate a partial transformation from tetragonal (high strain anisotropy) to rhombohedral (low strain anisotropy) at high electric field levels, with an average linear transformation strain of -1.54 × 10^-3. The domain switching behavior was effectively enhanced in both tetragonal and rhombohedral phases after the phase transformation, due to the release of intergranular stress. This observed self-adapting mechanism in tuning intergranular stress through partial phase switching in the morphotropic KBT-BF-PT composition with large lattice distortion could also be exploited in other perovskite systems in order to achieve high performance high temperature piezoelectric ceramics.     

Structural phase transition,electrical and photoluminescent properties of Pr3+-doped (1-x)Na0.5Bi0.5TiO3-xSrTiO3 lead-free ferroelectric thin films

Lead-free ferroelectric Pr³⁺-doped (1-x)Na_0.5Bi_0.5TiO₃-xSrTiO₃ (x?=?0–0.5) (hereafter abbreviated as Pr-NBT-xSTO) thin films were prepared on Pt/Ti/SiO₂/Si and fused silica substrates by a chemical solution deposition method combined with a rapid thermal annealing process at 700?°C, and their structural phase transition, dielectric, ferroelectric, and photoluminescent properties were investigated as a function of STO content. Raman analysis shows that with increasing STO content, the phase structures evolve from rhombohedral phase to coexistence of rhombohedral and tetragonal phases (i.e. morphotropic phase boundary), and then to tetragonal phase. The structural phase transition behavior has been well confirmed by temperature- and frequency- dependent dielectric measurements. Meanwhile, the variation in photoluminescence intensity of Pr³⁺ ions with different STO content in the NBT-xSTO thin films also indicates that there exists a clear structural phase transition when the film composition is close to the morphotropic phase boundary. Superior dielectric and ferroelectric properties are obtained in the Pr-NBT-0.24STO thin films due to the formation of morphotropic phase boundary. Our study suggests that Pr-NBT-xSTO thin films be promising multifunctional materials for optoelectronic device applications.     

Microstructure and piezoelectric properties of thermal sprayed Bi0.5(Na0.70K0.20Li0.10)0.5TiO3 ceramic coatings

The microstructure of Bi_0.5(Na_0.70K_0.20Li_0.10)_0.5TiO₃ (BNKLT) coatings fabricated by thermal spray method was closely examined by TEM, revealing the coexistence of rhombohedral and tetragonal perovskite main phases, and very minor secondary phases, while all amorphous phase was crystallized after heat treatment. Obtaining coexisting rhombohedral and tetragonal perovskite phases after the thermal spray process involving the melting-recrystallization and heat treatment process resulted in piezoelectric ceramic coating with excellent electrical and electromechanical properties. The effective piezoelectric coefficient d₃₃ of the heat-treated BNKLT coating reached 86?pm/V with substrate clamping, measured over macroscale by laser scanning vibrometer.     

Ferroelectric and ferromagnetic properties of Mn-doped 0.7BiFeO3–0.3BaTiO3 solid solution

Binary solid solutions 0.7BiFeO₃–0.3BaTiO₃–x wt.% MnO₂ (x = 0, 0.2, 0.3, and 0.5) were prepared by a traditional ceramic process. All ceramic samples show single perovskite phase. The effect of manganese doping on structure, dielectric, ferroelectric and ferromagnetic properties, and resistivity was investigated. Results show that Mn-dopant can improve the sintering ability of the materials when MnO₂ content is below 0.3 wt.%. When MnO₂ content exceeds 0.3 wt.%, the sintering ability is weakened and the phase structure of 0.7BiFeO₃–0.3BaTiO₃ solid solution changes from rhombohedral into tetragonal phase. With increasing concentration of MnO₂, the resistivity increases at first and then decreases. Whereas the coercive electric field decreases at first and then increases, the remanent magnetization M_r increases and the coercive magnetic field decreases.     

Structural properties of (Bi0.5Na0.5)1−xBaxTiO3 lead-free piezoelectric ceramics

A systematic XRD investigation of poled and unpoled ceramics of the system (1 ? x) Bi_0.5Na_0.5TiO₃–x BaTiO₃ (0 ≤ x ≤ 0.2) (BNBT) was performed. The variation of the lattice parameters confirms the existence of a morphotropic phase boundary at 0.06 ≤ x ≤ 0.08; however, significant differences in unit cell parameters between poled and unpoled states appear. Lattice distortions of the rhombohedral and tetragonal phases are significantly increased in poled samples. Dramatic changes in peak intensities of the pseudo-cubic (2 0 0) reflections between poled and unpoled samples reveal a strong enhancement of the tetragonal volume fraction in the poled state. Temperature-dependent XRD studies confirm a transition into a cubic high-temperature phase. This transition is rather smooth in the unpoled state. In poled samples, the tetragonal distortion and the tetragonal volume fraction display a different temperature variation and tetragonal regions seem to persist into the cubic phase field.     

New Lead‐Free (1 − x)(K0.5Na0.5)NbO3–x(Bi0.5Na0.5)ZrO3 Ceramics with High Piezoelectricity

For enhancing the piezoelectric properties of ceramics (Bi_0.5Na_0.5)ZrO₃ (BNZ) was used to partially substitute (K_0.5Na_0.5)NbO₃ (KNN). The addition of BNZ changes the symmetry of KNN ceramics from orthorhombic to tetragonal, and finally to rhombohedral phase. A new phase boundary with both rhombohedral–orthorhombic and orthorhombic–tetragonal phase transitions near room temperature is identified for KNN–0.050BNZ ceramics, where optimum electrical properties were obtained: d₃₃ = 360 pC/N, k_p = 32.1%, ε_r = 1429, tanδ = 3.5%, and T_C = 329°C. The results indicated a new method for designing high‐performance lead‐free piezoelectric materials.     

Ba(Zr_(0.055)Ti_(0.945))O_3含量对[(Na_(0.80)K_(0.16)Li_(0.04))_(0.5)Bi_(0.5)]TiO_3陶瓷性能的影响

系统研究(1-y)[(Na0.80K0.16Li0.04)0.5Bi0.5]TiO3-yBa(Zr0.055Ti0.945)O3无铅压电陶瓷,获得压电应变常数高达185pC/N的0.94[(Na0.80K0.16Li0.04)0.5Bi0.5]-TiO3-0.06Ba(Zr0.055Ti0.945)O3压电陶瓷。样品的晶体结构为三方相、四方相共存,处于准同型相界(morphotropic phase boundary,MPB)附近。该类陶瓷室温MPB的摩尔(下同)含量为0.050y0.065。样品y=0.060在40°左右的(003)、(021)双峰与46.5°左右的(002)、(200)双峰分裂最明显。随着Ba(Zr0.055Ti0.945)O3含量的增加,铁电相-反铁电相相变温度(θd)升高、反铁电相-顺电相相变温度(θm)降低;θd和θm的温差越来越小,材料的弛豫性逐渐降低。     

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.     

Structural and dielectric properties of (Na0.5Bi0.5)0.70Ba0.30TiO3 ceramics

A (Na_0.5Bi_0.5)_0.70Ba_0.30TiO₃ ceramic has been studied by X-ray diffraction and by measurements of dielectric and ferroelectric properties between room temperature and 450 °C. A sharp increase in the electric permittivity and dielectric loss near 200 °C has been observed. This sharp increase in dielectric responses indicates a transformation between normal and relaxor ferroelectric states. It is found that polar regions can exist at higher temperatures. The X-ray diffraction study shows that the transformation corresponds to the first order phase transition from tetragonal to cubic. The use of the (Na_0.5Bi_0.5)_0.70Ba_0.30TiO₃ ceramic for device application has also been indicated.