(1-x)(K0.5Na0.5)NbO3-xSrTiO3陶瓷的弛豫铁电性能

通过对（1-x）（K_0.5Na_0.5）NbO₃-xSrTiO₃（0≤x≤0.15）陶瓷的相组成、晶体结构和介电性能的研究发现,该陶瓷为单一的钙钛矿结构相.当x含量较小（x＜0.1）时为正交相结构,x≥0.1时转变为四方相结构.随着SrTiO₃掺杂量的增加,样品的致密度增加,样品由正常铁电相逐渐向弥散铁电相转变,且相 关键词： 弛豫铁电体 0.5Na_0.5）NbO₃铁电陶瓷')" href="#">（K_0.5Na_0.5）NbO₃铁电陶瓷 3掺杂')" href="#">SrTiO₃掺杂 相变温度     

(Bi0.5Na0.5)TiO3-Ba(Ti,Zr)O3 陶瓷的电性能研究

采用氧化固相法制备了(1-x)(Bi0.5Na0.5)TiO3-xBa(Ti0.95Zr0.05)O3(BNT-BZT)陶瓷,其中掺入量x的值分别为0,0.04,0.05,0.06,0.07.研究了BNT-BZT体系陶瓷的准同型相界以及陶瓷材料的微观结构和性能之间的关系,并探讨了陶瓷的介电性能和铁电等性能.通过探究Ba(Ti,Zr)O3(BZT)掺杂量对BNT 各性能的影响得出了当掺杂量x=0.05得到结构较为致密,介电,铁电性能较好的样本,对工业化研究和生产有重要的意义     

压电材料Na0.5K0.5NbO3高压相变的拉曼光谱研究

Na_0.5K_0.5NbO₃是一种不含铅的新型压电材料。理解该物质在高压下的晶体结构变化,有助于深入认识并提高其材料的稳定性及压电性能。然而目前关于该物质在高压下的相结构演化过程还缺少实验研究。本工作采用基于金刚石对顶砧(DAC)的高压拉曼光谱技术,研究了Na_0.5K_0.5NbO₃的高压拉曼光谱特性与压致相变行为。研究发现Na_0.5K_0.5NbO₃在高压环境下由于NbO₆八面体的振动模式发生改变,会依次发生正交相到四方相和四方相到立方相的可逆相变过程,其相变压力分别为4.0～5.5 GPa和5.5～6.4 GPa。     

(1-x)PMN-xPT铁电致冷陶瓷的研究

概括介绍了铁电致冷基本原理，给出了三种电生热效应，即线性电生热效应、二次电生热效应和电场诱导一级相变型电生热效应的表达式，测量了(1-x)Pb(Mg_1/3 Nb_2/3 )O₃-xPbTiO₃［简记为(1-x)PMN-xPT］，当x=0.08, 0.10和0.25时在室温附近的电生热性能，分析了其电生热效应的起源.研究结果表明，(1-x)PMN-xPT铁电固溶体陶瓷在室温附近具有较大的电生热效应；该效应起源于电场诱导一级相变型电生热效应和线性电生热效应；该系列陶瓷可望用于室温附近多级铁电致冷. 关键词：     

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     

单相Na0.5Bi0.5Ti1-xMnxO3陶瓷中的多铁性

溶胶凝胶法制备了Na0.5Bi0.5Ti1-xMnxO3(x=0,0.02,0.04)陶瓷样品,X射线衍射(XRD)分析表明陶瓷样品均形成了单一的钙钛矿(ABO3)型结构且没有杂质相的形成.随着Mn含量的增加,XRD峰向高角度方向移动,表明Mn离子进入Na0.5Bi0.5TiO3晶格.掺杂样品均表现出室温铁磁性和铁电性.磁测量表明样品中存在复杂的磁相互作用,包括铁磁,反铁磁和顺磁相互作用.以上结果表明,通过Mn的掺杂可以使铁电材料Na0.5Bi0.5TiO3转变为多铁材料.     

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.     

(Bi, La)4Ti3O12-Sr(Bi, La)4Ti4O15共生结构铁电材料性能研究

采用固相烧结工艺,制备了不同La掺杂量(x=0.00,0.25,0.50,0.75,1.00,1.25和1.50)的(Bi, La)4Ti3O12-Sr(Bi, La)4Ti4O15 (SrBi8-xLaxTi7O27)共生结构铁电陶瓷样品.用x射线衍射对其进行微结构分析,并测量铁电、介电性能.结果发现,La掺杂未改变Bi4Ti3O12-SrBi4Ti4O15共生结构铁电材料的晶体结构.随掺杂量的增加,样品的矫顽场(Ec)略有增加,剩余极化(2Pr)先增大,后减小.在x＝0.50时,2Pr达到极大值,为25.6 μC*cm-2,与Bi4Ti3O12-SrBi4Ti4O15相比,2Pr增加了近60%,而Ec仅增加约10%.随La掺杂量的增加,样品的居里温度TC逐渐降低,x＝0.50时,TC=556 ℃.在x=1.50时,样品出现弛豫铁电体的典型特征.     

Bi0.5Ba0.5FeO3 陶瓷的电性能及阻抗分析

以传统的固相反应法制备了Bi_0.5Ba_0.5FeO₃陶瓷,并采用X射线衍射仪、扫描电子显微镜、直流阻温测试仪和交流阻抗分析仪测试了Bi_0.5Ba_0.5FeO₃陶瓷的微结构和电性能.分析结果表明:Bi_0.5Ba_0.5FeO₃陶瓷具有立方钙钛矿结构,颗粒尺寸约1.0 μm;在16—280 ℃范围内,Bi_0.5Ba_0.5FeO₃陶瓷表现出明显的负温度系数热敏效应,其热敏常数、活化能分别为6490 K及0.558 eV;介电温谱揭示,在280 ℃下Bi_0.5Ba_0.5FeO₃陶瓷材料没有出现相变行为.对于交流阻抗谱,采用3个串联的RQ(R与Q为并联)等效部件来拟合分析,拟合结果表明拟合数据与实验数据高度匹配,且这3个等效部件分别代表晶界、晶粒和晶壳的贡献.3个部件中,晶粒对陶瓷电阻阻值的影响最大,晶壳贡献次之,晶界最小,且3个部件电阻值都显示出负温度系数效应.在25—115 ℃范围内,电学模量虚部峰频与阻抗虚部峰频始终不匹配,意味着Bi_0.5Ba_0.5FeO₃陶瓷体内部一直表现出局域导电机理. 关键词： 0.5Ba_0.5FeO₃陶瓷')" href="#">Bi_0.5Ba_0.5FeO₃陶瓷 电性能 阻抗分析     

La诱导(Pb(1-3x/2)Lax)(Zr0.5Sn0.3Ti0.2)O3反铁电介电弛豫研究

采用标准电子陶瓷工艺制备了(Pb_(1-3x/2)La_x)(Zr_0.5Sn_0.3Ti_0.2)O₃(PLZST,0.00≤x≤0.18)反铁电陶瓷,利用X射线衍射、不同频率下弱场介电温谱、强场下的极化强度-电场(P-E)测试研究了材料相结构和电学性能.实验结果发现,随La含量x增大,室温下材料由铁电三方相(关键词： 反铁电陶瓷 介电频率色散 相变弥散 介电弛豫     

Structural and dielectric properties of La- and Ti-modified K0.5Na0.5NbO3 ceramics

We report the results of studies of rectifying behavior, positive magneoresistance (MR), the charge-transport mechanism and the effect of an electric field on a ZnO (n)/La_0.5Pr_0.2Sr_0.3MnO₃ (LPSMO) (p)/SrNb_0.002Ti_0.998O₃ (SNTO) (n) heterostructure comprising two p–n junctions fabricated using the pulsed laser deposition technique. The heterostructure exhibits rectifying behavior over a wide temperature and field range having hysteresis in I–V behavior (forward bias) due to the tunneling of charge carriers. It is also observed that, depending on the nature of the electric field bias to n-type ZnO and SNTO, the junction resistance becomes modified, which has been explained on the basis of spin injection in the heterostructure. The observation of unconventional positive MR at room temperature has been justified on the basis of interface effects and the reduction in barrier height obtained using fitting of the I–V data by a thermionic emission model.     

Enhanced piezoelectric properties near the morphotropic phase boundary in lead-free (1-x)(Bi0.5K0.5)TiO3-xBi(Ni0.5Ti0.5)O3 ceramics

Lead-free piezoelectric ceramics of the composition (1-x)(Bi_0.5K_0.50)TiO₃-xBi(Ni_0.50Ti_0.50)O₃ or (1-x)BKT-xBNiT (when x = 0–0.20 mol fraction) were prepared by a conventional mixed-oxide method and sintered at 1050 °C for 4 h. The effects of BNiT content on the phase equilibria, and the dielectric, ferroelectric and piezoelectric properties were systematically investigated. High density sintered specimens (5.71–6.12 g/cm³) were obtained for all compositions. X-ray diffraction patterns showed that all BKT-BNiT samples exhibited a single perovskite phase which confirms that BNiT and BKT formed a solid solution up to x = 0.20. A morphotropic phase boundary (MPB) separating a BKT-rich tetragonal phase and a BNiT pseudo-cubic phase was identified over the compositional range 0.05 < x < 0.10, where enhanced electrical properties were observed. The optimum dielectric properties (ε_r = 1710, tanδ = 0.036), ferroelectric properties (P_r = 16.6 μC/cm², E_c = 22.5 kV/cm and R_sq = 0.86) and piezoelectric properties (d₃₃ = 288 pC/N, S_max = 0.22% and d^*₃₃ = 313 pm/V) were observed with a relatively high T_m ∼ 304 °C within this MPB region. Overall, these results indicate that the BKT-BNiT ceramic system is a promising lead-free piezoelectric candidate for further development for actuator applications.     

Sintering and electrical properties of Na0.5K0.5NbO3 ceramics modified with lanthanum and iron oxides

Effects of La³⁺, Fe³⁺ doping and their co-doping on the sintering, structures and electrical properties of Na_0.5K_0.5NbO₃ (NKN) ceramics were investigated. A significant modification of sintering behavior can be obtained by the addition of Fe₂O₃. On the contrary, the addition of La₂O₃ and La–FeO₃ tends to degrade the densification. Moreover, Fe³⁺ doping does not change the crystal structure, thus leading to an unchanged Curie temperature. Owing to a transition from orthorhombic to pseudo-cubic structures, the Curie temperatures of NKN ceramics were significantly lowered by doping La₂O₃ and La–FeO₃. NKN ceramics modified with a small amount of Fe₂O₃ and La–FeO₃ (less than 0.5 mol%) exhibit improved ferroelectric, piezoelectric and electromechanical properties.     

New crystallographic dielectric phase boundary in K0.5Na0.5NbO3‐based lead‐free ceramics

0.979K_0.5Na_0.5Nb_1‐xSb_x O₃‐0.021Bi_0.5Na_0.5TiO₃ (KNNSx ‐BNT) lead‐free piezoelectric ceramics were fabricated by conventional solid state reaction technique, and their phase transition and electrical properties were studied. With the increase of x, the rhombohedral‐orthorhombic phase transition temperature of the ceramics increases. Finally, both the rhombohedral‐orthorhombic and orthorhombic‐tetragonal phase transitions of the ceramics were modified to be around room tempera‐ ture when about 6% Sb were substituted for the Nb site, resulting in the formation of a new phase boundary separating rhombohedral and tetragonal phases. The formation of the new phase boundary results in excellent properties for the ceramics, that is, the KNNS0.05‐BNT ceramic shows an enhancement in piezoelectric properties: d₃₃ = 380 pC/N and k_P = 0.438. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and physical properties of Ca- and Ta-modified (K,Na)NbO3 lead-free piezoelectric ceramics

Polycrystalline samples of lead-free Ca and Ta co-substituted potassium sodium niobate (K_0.5Na_0.5NbO_3, KNN) ceramics have been prepared by solid state reaction technique. X-ray diffraction showed formation of a single-phase perovskite structure with orthorhombic symmetry. Substitution inhibits the grain growth, improves densification and decreases the ferro-paraelectric phase transition temperature. Temperature dependent dielectric permittivity studies demonstrate significant decrease in peak-permittivity values in the substituted samples. Bulk longitudinal piezoelectric coefficient is significantly enhanced, up to ～155 pC/N for (K_0.48Na_0.48Ca_0.02)(Nb_0.85Ta_0.15O₃) as compared to 95 pC/N for pristine KNN ceramic. Local piezoelectric properties have been observed by piezoresponse force microscopy (PFM) technique. Distinct piezocontrast was studied in both vertical and in-plane modes of PFM for all samples. The samples exhibit self-polarization effect in the unpoled state and effective local vertical piezoelectric coefficient was the largest in Ca and Ta co-substituted sample whereas the in-plane piezoelectric coefficient was maximum for Ca-substituted KNN sample. These studies are important for using substituted lead free KNN materials in various piezoelectric applications.     

Raman tensor analysis of (K0.5Na0.5)NbO3–LiSbO3 lead‐free ceramics and its application to study grain/domain orientation

A quantitative polarized Raman analysis of ferroelectric grain/domain orientation in LiSbO₃ (LS‐modified) (K_0.5Na_0.5)NbO₃ (KNN) ceramics is presented, based on the analysis of the complex orientation dependence in space of their Raman‐active modes. Complete sets of Raman tensor elements of A_g, and E_g phonon modes for orthorhombic/tetragonal structures of KNN have been determined. Through this spectroscopic algorithm, quantitative information could be extracted in terms of three Euler angles in space for KNN samples consisting of mixed phases, thus enabling quantitative visualization of the local distribution of grains/domains in the solid angle. As an application of the method, we quantitatively examined the unknown crystallographic grain orientation patterns on the surfaces of pure KNN and of KNN‐0.05LS ceramics. These two samples were useful to clarify a polymorphic phase transition from the orthorhombic to the tetragonal phase taking place in the LS‐modified KNN system. Thus, we demonstrated that polarized Raman spectroscopy is a valuable and efficient tool for nondestructive three‐dimensional assessments of grain/domain orientation in ferroelectric materials with complex polymorphic structures. We believe that the data shown here represent a typical scenario encountered in grain/domain orientation assessments of piezoelectric perovskites. Copyright © 2012 John Wiley & Sons, Ltd.     

Piezoelectric and ferroelectric properties of [(K0.4725Na0.4725)Li0.055]NbO3–(Ag0.5Li0.5)TaO3 lead‐free ceramics

New lead‐free piezoelectric (1 – x)[(K_0.4725Na_0.4725)Li_0.055]NbO₃– x (Ag_0.5Li_0.5)TaO₃ [(1 – x)KNNL–x ALT] ceramics were prepared by conventional sintering. Piezoelectric and ferroelectric properties and Curie temperature of the ceramics were studied. The (1 – x)KNNL–x ALT (x = 0.04) ceramics exhibit good properties (d₃₃ ～ 252 pC/N, k_p ～ 41%, T_C ～ 471 °C, T_o–t = 47 °C, P_r = 33.1 μC/cm², E_c = 10.6 kV/cm). These results show that (1 – x)KNNL–x ALT (x = 0.04) ceramic is a promising lead‐free piezoelectric material for high temperature application. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystalline structural phase boundaries in (K,Na,Li)NbO 3 ceramics

Lead-free (K_xNa_1−x)_1−yLi_yNbO₃ ceramics (with x=0.50, y=0–0.08 and x=0.30–0.70, y=0.06, respectively) were synthesized using the conventional solid-state reaction technique. Compositional influences of K, Na and Li constituents on microstructures, crystalline structures, dielectric and piezoelectric properties were investigated. It has been known that microstructures change largely with the alkali constituents and that there exist three orthorhombic-tetragonal phase boundaries at room temperature. One occurs in (K_0.50Na_0.50)_1−yLi_yNbO₃ ceramics at y=0.05–0.06, which corresponds to the previously reported morphotropic phase boundary (MPB). The other two appear in (K_xNa_1−x)_0.94Li_0.06NbO₃ ceramics near x=0.40 and x=0.60, respectively. (K_0.50Na_0.50)_0.935Li_0.065NbO₃ and (K_0.45Na_0.55)_0.94Li_0.06NbO₃ ceramics show high piezoelectric properties with the d₃₃ values over 200 pC/N and the k_p values around 45% at room temperature. It is thought that the observed high piezoelectric properties are largely affected by the temperature-driven orthorhombic-tetragonal phase transition.     

溶胶-凝胶法制备的高压电常数(Bi_(0.5)Na_(0.5))_(1-x)Ba_xTiO_3系无铅压电陶瓷

测量了使用溶胶 凝胶工艺制备的 (Bi0 5Na0 5) 1 -xBaxTiO3(x =0 0 0 ,0 0 4 ,0 0 6 ,0 0 8,0 12 )系陶瓷的介电、压电、铁电和热释电性能 .由于使用了溶胶 凝胶工艺制备的粉料 ,因此所有样品的压电性能都得到了较大提高 .其中(Bi0 5Na0 5) 0 94 Ba0 0 6 TiO3系陶瓷具有该系列最大的压电常数 ,d33=173× 10 - 1 2 C N ,与传统工艺相比 ,d33提高了近4 0 % .同时 ,在一定范围内 ,随Ba含量的增加 ,材料的剩余极化Pr 和矫顽场Ec 逐渐减小 ,退极化温度逐渐降低 .对于 (Bi0 5Na0 5) 0 94 Ba0 0 6 TiO3系陶瓷 ,剩余极化和矫顽场分别为 2 5 μC cm2 和 2 8kV cm ,退极化温度约为 80℃ .