Nanostructured Ceramics of Potassium Sodium Bismuth Titanate: Hydrothermal Synthesis and Piezoelectric Response at Morphotropic Phase Boundary

Potassium Sodium Bismuth Titanate (KNBT) ceramics, with the general formula (1 - x)K0.5Bi0.5TiO3 -xNa0.5Bi0.5TiO3, have been synthesized following hydrothermal route, starting with solid solutions of pure perovskite nanoceramics of KBT and NBT in desired stoichiometric weight ratios, followed by sintering between 850°C and 1000°C for few hours. Pure KNBT nanoceramics with perovskite structure, having mean particle size around 30 nm, could be obtained. Morphology of the samples is found to depend strongly on composition. A change of composition results in a phase change, as evident from X-ray structure analysis. This phase change is a result of rhombohedral to tetragonal morphotropic phase boundary (MPB) in the sample with x around 0.80. Composition dependent occurrence of MPB leads to formation of needle like structures with micrometer length scales. These are typical of tetragonal lamellar structures, suggesting partial induction of tetragonal polar order from rhombohedral structure at MPB. Dielectric and piezoelectric properties, such as dielectric constant and loss, piezoelectric coefficients and figures of merit, exhibit threshold maxima in their values at the composition corresponding to MPB. These values reported for a lead-free piezoceramic, synthesized by a comparatively simple hydrothermal route, are highly promising, and comparable to well-known PZT.

准同型相界(MPB)附近BS-PT高温压电陶瓷研究

(1-x)BiScO3-xPbTiO3陶瓷(简记BS-PT)在x=64．0％附近存在一个从菱方晶系过渡到四方晶系的准同型相界,在此相界附近材料能获得优良的介电和压电性能．本文选取PbTiO3含量在64．0％-65．5％的准同型相界附近的材料组分,利用传统的固相烧结反应法合成了纯钙钛矿相结构的BS-PT陶瓷,通过对材料的相结构形成过程和内部形貌分析以及对介电、压电性能的研究,发现在x=64．5％的组分条件下,BS-PT陶瓷材料获得了准同型相界范围内的最优的压电性能,其室温压电常数d33可达500pC／N,且居里温度(Tc)达到了438℃,剩余极化强度和电致应变分别为44μC／cm2和3．5‰．研究表明,准同型相界附近的BS-PT陶瓷是一种优良的压电换能器和传感器材料．

具有准同型相界(MPB)组成的化合物(Sr_(1-x)Ba_x)_2NaNb_5O_(15)的晶体生长及性质研究

用Czochralski方法生长出铁电钨青铜型单晶 (Sr1-xBax) 2 NaNb5O15(简称SBNN) ,晶体沿c轴方向生长。正交 四方相的准同型相界 (简称为MPB)存在于x =0 .4 5～ 0 .5 0之间 ;SBNN晶体是不一致熔融的化合物 ,在晶体成长过程中 ,Sr2 + 的分凝系数比Ba2 + 的大 ,因此具有高浓度Ba2 + 的SBNN晶体很难生长。晶体的居里温度是 2 4 3℃ ,在此温度下的相变是弥散的 ,随频率的增加 ,介电常数降低。

Microstructure,crystalline phase and electrical properties of Li_(0.06)(Na_(0.5)K_(0.5))_(0.94)Nb_(1-2x/5)Mg_xO_3 lead-free piezoelectric ceramics

MgO-modified Li0.06（Na0.5K0.5）0.94NbO3O3 （L6NKN） lead-free piezoelectric ceramics were synthesized by normal sintering at a rela- tively low temperature of 1000℃. The crystalline phase, microstructure, and electrical properties of the ceramics were investigated with a special emphasis on the influence of MgO content. The addition of MgO effectively improves the sintembility of the L6NKN ceramics. X-my diffr cfion analysis indicates that the morphotropic phase boundary （MPB） separating orthorhombic and tetragonal phases for the ceramics lies in the range of Mg doping content （x） from 0.3at% to 0.7at%. High electrical properties of the piezoelectric constant （d33=238 pC/N）, planar electromechanical coupling coefficient （kp=41.5%）, relative dielectric constant （εr=905）, and remanent polarization （Pr=38.3 μC/cm2） are obtained from the specimen with x=0.5at%, which suggests that the Li0.06（Na0.5K0.5）0.94Nb（1-2x/5）MgxO3 （x=0.5at%） ceramic is a promising lead-free piezoelectric material.

Cu^(2+)调控MPB对NBT基陶瓷压电性能的影响

采用传统固相法制备(Na_(0.47)Bi_(0.47)Ba_(0.06))Ti_(1-x)Cu_(x)O_(3)(NBT-6BT-xCu^(2+),0≤x≤0.025)无铅压电陶瓷。研究了不同含量Cu^(2+)对NBT-6BT-xCu^(2+)陶瓷样品结构以及电学性能的影响。SEM结果显示陶瓷晶粒的大小与Cu^(2+)掺入量有关;XRD数据表明Cu^(2+)可以固溶进陶瓷晶格,并且所有样品均为钙钛矿结构;对XRD进行Rietved全谱拟合后发现,所有陶瓷样品具有单斜(Cc)和四方(P4bm)两相,均位于准同型相界(MPB);Cu^(2+)的掺入对MPB处Cc和P4bm相含量造成影响,使得压电和铁电性能增强。在x=0.015时,样品具有最佳的电学性能:压电常数(d_(33))达到178 pC/N,剩余极化强度(P_(r))达到42.93μC/cm^(2)。结果表明,Cu^(2+)可以通过调控MPB处相含量,很好地提高(Na_(0.47)Bi_(0.47)Ba_(0.06))TiO_(3)无铅压电陶瓷的电学性能。

Effects of Na/K ratio on the phase structure and electrical properties of Na_xK_(1-x)NbO_3 lead-free piezoelectric ceramics

Lead-free piezoelectric NaxK1-xNbO3（x = 0.3-0.8）（NKN） ceramics were fabricated by normal sintering at 1060°C for 2 h.Microstructures and electrical properties of the ceramics were investigated with a special emphasis on the influence of Na content.The grain size of the produced dense ceramic was decreased by increasing Na content.A discontinuous change in the space distance was found at the composition close to Na0.7K0.3NbO3 ceramic, which indicates the presence of a transitional composition between two different orthorhombic phases, which is similar to the behavior of morphotropic phase boundary（MPB） in NaxK1-xNbO3 ceramics.Such MPB-like behavior contributes to the enhanced piezoelectric coefficient d33 of 122 pC/N, planar-mode electromechanical coupling coefficient kP of 28.6%, and dielectric constant εr of 703, respectively for the Na0.7K0.3NbO3 ceramic.Cubic temperature TC and the transitional temperature TO-T from orthorhombic to tetragonal phase are observed at around 420°C and 200°C, respectively.

SPS中压力对PZT陶瓷准同型相界(MPB)的影响

采用放电等离子烧结的方法制备了准同型相界(Morphotropic Phase Boundary,MPB)组分的Pb(Zr_(0.52)Ti_(0.48))O_(3)压电陶瓷,研究了放电等离子的压力对材料中菱面体相和四方相比例的影响.研究结果表明:当在30 MPa下采用放电等离子烧结制备PZT压电陶瓷时,晶体结构处于菱面体相和四方相的混合状态,并且最接近于准同型相界(MPB),其自发极化达到:P s=75.265μC/cm^(-2),压电性能也是所有压力中最高的:d_(33)=136.9 pC/N.证明了压力对于晶体结构有一定的影响,可以调控处在准同型相界附近材料中的菱面体相和四方相的比例,进一步提升材料的性能.

Effects of Thermal Conditions in the Phase Formation of Undoped and Doped Pb(Zr_1-xTi_x)O₃Solid Solutions

The purpose of this research is to study the effect of thermal conditions such as temperature ramp rate and isothermal times in the phase formation of Pb(Zr1-xTix)O3 solid solutions with composition near the morphotropic phase boundary (MPB) by using the conventional ceramic method. The perovskite phase formation and morphology of undoped Pb(Zr0.52Ti0.48)O3 (abbreviated PZT) and doped new material Pb0.98Gd0.02[(Zr0.52Ti0.48)0.98(Mg1/3Nb2/3)0.01(Ni1/3Sb2/3)0.01]O3 (abbreviated PZT-PGMNNS) specimens calcined between 700°C and 900°C have been examined by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier Transform Infrared (FTIR) while the thermal evolution of the initial precursor was followed by TG-DTA. So the results of these studies have been discussed.

钛酸铋钠基无铅压电陶瓷掺杂改性研究现状

钛酸铋钠(Bi_(0.5)Na_(0.5)TiO_(3),简称BNT)基无铅压电陶瓷因其环境友好型、良好的铁电压电性能等特点在航空航天、舰艇声纳、高速列车及电子产品等领域得到广泛应用。为了克服钛酸铋钠基无铅压电陶瓷高矫顽场并进一步提升其电学性能,通过对BNT基无铅压电陶瓷进行掺杂改性构建三方相–四方相共存的准同型相界(MPB)。掺杂改性是改善BNT基无铅压电陶瓷性能的一种重要方法,针对BNT基无铅压电陶瓷掺杂改性进行系统总结十分必要。主要从BNT基无铅压电陶瓷多组元改性、A/B位离子掺杂和稀土离子掺杂改性等三方面综合论述近年来BNT基压电陶瓷研究进展。结果表明,引入合适的组元有利于BNT基无铅压电陶瓷构建三方相–四方相共存的准同型相界;A/B离子掺杂是根据离子半径和电价大小的一致性对BNT陶瓷中对应位置的离子进行取代;稀土离子掺杂主要对该陶瓷的光电特性有显著影响。上述三方面从不同角度改善了BNT基无铅压电陶瓷的性能,以期为研究性能更好的BNT基无铅压电陶瓷的科研和技术人员提供参考,并为BNT基无铅压电陶瓷的实际应用奠定基础。

Synergy of lead vacancies and morphotropic phase boundary to promote high piezoelectricity and temperature stability of PBZTN ceramics

The flourishing development of emerging electromechanical applications has stimulated an urgent demand for ferroelectric ceramics with high piezoelectric properties and broad temperature usage range.However,it remains a challenge to simultaneously obtain good piezoelectricity and reliable temperature stability in lead zirconate titanate(PZT)-based piezoelectric ceramics.To solve this issue,a synergetic strategy was proposed to introduce lead vacancies through niobium doping and construct morphotropic phase boundary(MPB).In this work,Pb_(0.905)Ba_(0.085)(V Pb″)_(0.01)[(Zr_(x)Ti_(1-x))_(0.98)Nb_(0.02)]O_(3)(PBZTN-x)material system was designed.Good comprehensive properties(d_(33)=864 pC/N,k_(p)=84%,T_(C)=201℃)and excellent temperature stability(less than 10%variation of electrical properties from 20℃ to 160℃)were obtained in PBZTN-0.540 ceramics.Good piezoelectricity can be attributed to high extrinsic contribution(domain wall motion)induced by Pb^(2+)vacancies and the existence of nano-domains emerged at MPB,while excellent temperature stability is mainly attributed to the minimized local stress in the lattice and the stable domain structure.

Dielectric properties of Pb (Zn_(1/3) Nb_(2/3)) O_3-PbZrO_3-PbTiO_3 solid solution near morphotropic phase boundary

The dielectric properties of Pb(Zn1/3Nb2/3)O3-PbZrO3-PbTiO3 (PZN-PZ-PT) system near the rhombohedral/tetragonal morphotropic phase boundary (MPB) are carefully studied in this paper.It is found that,for all samples,the curves around the temperatures of dielectric permittivity peak show the characteristics of diffuse phase transition.The change in PbZrO3/PbTiO3 ratio has much influence on the dielectric properties of the samples.The extent of diffuse phase transition increases with the increasing Zr/Ti ratio.The samples in rhombohedral region have typical diffuse phase transition in the temperature range measured.However,for the samples with tetragonal symmetry,a spontaneous normal ferroelectric-relaxor phase transition exists at temperature lower than that of permittivity peak.This normal ferroelectric-relaxor phase transition is confirmed by the experiment of thermally driven current.The analysis of TEM reveals that the samples in tetragonal region show a 90° macrodomain structure,while the samples in rhombohedral region have the configuration of microdomain structure.

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.

ertical morphotropic phase boundary in lead-free piezoelectric ceramics(K,Na,Li)NbO_(3)-BaZrO_(3)-(La,Na)TiO_(3) system

A morphotropic phase boundary(MPB)with temperature-independent behavior,the so-called vertical MPB was investigated in lead-free(K,Na,Li)NbO_(3)–BaZrO_(3)–(La,Na)TiO_(3)ternary ceramic system.The specimens were synthesized by a conventional solid-state reaction method,and their crystal structures as well as their MPB were determined from X-ray diffraction patterns measured from room temperature to 300℃.The vertical MPB composition was determined to be 0.9025(K_(0:45)Na0:5Li_(0:05))NbO_(3)–0.09BaZrO_(3)–0.0075(La,Na)TiO_(3)and the Curie temperature was found to be about 195℃.It was successfully confirmed that ceramic samples of this system could be sintered in a reducing atmosphere.For lead-free piezoceramic applications of multilayer actuators using Ni inner electrodes,the results obtained in this work have important practical implications.

MORPHOTROPIC PHASE BOUNDARY AND DIELECTRIC RELAXATION STUDY OF(Bi_(0.5)Na_(0.5))TiO_(3)-BaTiO_(3)LEAD-FREE CERAMIC

We report the temperature and frequency dependence impedance spectroscopy of(1-x)(Bi_(0.5)Na_(0.5))TiO_(3-x)BaTiO_(3)(abbreviated as BNT-BT)ceramics with 0≤x≤0.07 prepared by conventional solid-state route.X-ray diffraction analysis indicated that a solid solution is formed when BaTiO_(3)diffuses into the(Bi_(0.5)Na_(0.5))TiO_(3)lattice and a morphotropic phase boundary between rhombohedral and tetragonal locates at x=0.07.The microstructure indicated that the grain size reduces and the shape changes from rectangular to quasi-spherical with increase in BaTiO_(3)content.Complex Impedance Spectroscopy analysis suggested the presence of temperature-dependent relaxation process in the materials.The modulus mechanism indicated the nonDebye type of conductivity relaxation in the materials,which is supported by impedance data.The activation energies have been calculated from impedance,electric modulus studies and dc conductivity which suggests that the conductions are ionic in nature.The activation energy increases with increase of BT content up to x=0.05 and decreases at x=0.07 which also indicates the presence of morphotropic phase boundary at x=0.07.

铈掺杂对PSN-PZN-PMS-PZT压电陶瓷性能的影响

采用二次合成工艺制备PSN-PZN-PM S-PZT五元系压电陶瓷。研究准同型相界组成点处铈掺杂对压电陶瓷介、压电性能影响。结果发现随着C eO2的添加,介电常数增加,居里温度降低;压电常数增加;机械品质因数和机电耦合系数下降;铈掺杂在强场下对该系统介电性能的影响基本上和弱场下的变化趋势相近,随着外加场强的增加,介电常数和介电损耗增加。

Na_(1/2)Bi_(1/2)TiO_3-BaTiO_3系陶瓷压电性及弛豫相变研究

系统研究了（１－ｘ）Ｎａ１／２Ｂｉ１／２ＴｉＯ３－ｘＢａＴｉＯ３（ｘ＝０．０２、０．０４、０．０６、０．０８、０．１０）无铅压电陶瓷系统的相界、材料压电性能，弛豫特性及相变．这个系统的陶瓷材料具有Ｋｔ／Ｋｐ较大，频率常数比较高等特点．Ｘ－ｒａｙ衍射结构分析发现此系统的相界在０．０４＜ｘ＜０．０６之间；材料的一些主要性能在相界附近达到极值．利用介电系数－温度曲线，并结合热激电流曲线对此系统的弛豫性进行研究和分析；初步研究了各配方组成的铁电－顺电的相变过程，发现在一定的组成范围内，材料在由铁电相向顺电相的转变过程中经历了一个过渡相区．

PMN-PT系陶瓷的熔盐法合成及其压电性能研究

采用熔盐法合成在多晶相界附近的ＰＭＮ－ＰＴ系陶瓷样品，对其压电性能进行了研究，并与传统陶瓷工艺进行了比较．结果表明：熔盐法得到的样品的压电性能较好，Ｋｐ＝５８％，ｄ３３＝５２０ｐＣ／Ｎ；而传统陶瓷工艺得到的陶瓷样品的Ｋｐ＝４６％，ｄ３３＝３６７ｐＣ／Ｎ．采用ＳＥＭ和ＸＲＤ等手段对结果进行了分析和讨论．

弛豫铁电材料在准同型相界附近结构和性能研究的最新进展

铅系钙钛矿结构弛豫铁电材料在准同型相界区域的单晶,因为具有优异的介电、压电性能及潜在的应用前景,近年来已经引起了广泛的重视,本文较详细地介绍了其反常性能的一些特征,以及对其起源在理论及实验观察上的最新进展,重点介绍了自发极化在外场下进行偏转的理论,以及近年来用同步辐射的Ｘ射线衍射实验研究结果,发现在原先以为只有菱方相和四方相的准同型相界区域存在着单斜相．

PNW-PMS-PZT压电陶瓷准同型相界的压电性能研究

采用传统陶瓷工艺制备了PNW—PMS—PZT四元系压电陶瓷,分析了陶瓷样品的相结构组成,结果表明,所有陶瓷样品的相结构为纯钙钛矿相结构;研究了室温下PMS含量,PNW 含量和Zr/Ti的变化对准同型相界的影响规律,实验表明随着PMS、PNW含量和Zr/Ti的增加,材料体系逐渐由四方相向三方相过渡,获得了处于准同型相界附近的材料组成:PMS 的含量在5—6mol%、PNW的含量在2—3mol%、PZT的含量在91—93mol%、Zr/Ti的变化靠近50/50,同时具有高的机电性能.

PSN-PZN-PMS-PZT五元系压电陶瓷性能的研究

采用二次合成工艺得到了PSN-PZN-PM S-PZT五元系压电陶瓷。实验数据表明:组成在准同型相界处压电陶瓷的综合性能达最佳。在此基础上,分析组成在准同型相界处压电陶瓷的烧结温度与体密度、气孔率、晶粒大小及介电、压电性能的关系。结果表明,在合成温度为860°C时可得到钙钛矿结构。烧结温度1 260°C保温3 h条件下,得到一种综合性能优良的压电材料。主要参数为:3Tε3/0ε=1390,tanδ=0.32%,d33=303 pC/N,kp=55.1%,Qm=1 180。定量S r2+、B a2+的加入使相界向富锆方向移动,性能参数为,3Tε3/0ε=1 162,tanδ=0.30%,d33=307 pC/N,kp=56.8%,Qm=1 230。