锆钛酸铅95/5薄膜的介电性能与弛豫特征

采用溶胶-凝胶法制备锆钛酸铅95/5（PZT95/5）薄膜,通过分析介电温度谱、介电频谱研究薄膜的介电性能.研究结果表明：介电常数-温度曲线ε（T）的相变峰随着频率的增加而逐渐变得平坦.同时,介电常数倒数与温度曲线ε-1（T）在高频不符合居里外斯定律;采用普适弛豫定律公式,对不同温度下的介电频谱曲线ε（f）进行拟合,得到弥散系数随着温度的变化曲线,该曲线在铁电-顺电转变以及反铁电-铁电转变这两个特征温度附近出现异常,结合材料反铁电-铁电-顺电相变的微观结构变化规律对此现象进行了讨论.     

铁微量掺杂对二钛酸钡陶瓷介电性能的影响

采用常规固相反应法,以碳酸钡、二氧化钛和三氧化二铁为原料,制备微量铁掺杂的二钛酸钡陶瓷,研究了铁掺杂含量对二钛酸钡陶瓷的相纯度、相对密度和介电性能的影响.采用X射线粉末衍射仪检测二钛酸钡陶瓷的相成分,利用精密阻抗分析仪测量其介电性能.结果表明,微量铁元素进入了二钛酸钡晶格,能够获得单相二钛酸钡陶瓷的最大铁掺杂量在0.5%～1%之间.随着铁含量的增加,铁电相变居里温度快速减小,从未掺杂时的415 ℃降至铁含量为0.02%时的376 ℃和铁含量为0.5%时的324 ℃.同时介电常数逐渐减小,介电峰不断发生宽化,但并没有导致弛豫性铁电体的出现.微量铁元素的掺杂在实验测量误差范围内对陶瓷的密度影响不大.     

(Ba_(0.94)La_(0.06))Ti_(0.985)O_3陶瓷的低温相变点的确定

为了对国产X射线衍射仪(XRD)进行低于室温的温度校正,采用冷压陶瓷技术制备了(Ba1-xLax)Ti1-x/4O3(x=0.06)(BL6T)陶瓷样品.BL6T陶瓷的铁电相变点(TC)由升温的介电温谱和降温的拉曼光谱技术确定.结果表明:BL6T具有一级相变特征,符合变温XRD校正要求.但BL6T显示热弛豫效应,采用两种技术确定的相变点分别发生在-3和-6℃,两者显示较小的热弛豫(3℃).     

Sol-Gel法制备择优取向铁电陶瓷薄膜的研究进展

综述了溶胶—凝胶法制备择优取向铁电陶瓷薄膜的研究现状,主要介绍了制备过程中衬底材料、热处理工艺、前驱体以及掺杂等因素对铁电陶瓷薄膜择优取向的影响以及铁电陶瓷薄膜的择优取向与铁电性能的关系。     

Sol-Gel法制备择优取向铁电陶瓷薄膜的研究进展

综述了溶胶—凝胶法制备择优取向铁电陶瓷薄膜的研究现状,主要介绍了制备过程中衬底材料、热处理工艺、前驱体以及掺杂等因素对铁电陶瓷薄膜择优取向的影响以及铁电陶瓷薄膜的择优取向与铁电性能的关系。     

铈掺杂钛酸铋陶瓷铁电与介电性质研究

采用固相烧结工艺制备了铈(Ce)元素掺杂钛酸铋(Bi4Ti3O12)材料构成Bi4Ti3-xCexO12(x=0,0.015,0.03,0.06)铁电陶瓷材料并研究其介电以及铁电性质.晶格常数随着掺杂浓度的变化,意味着Ce4+/Ce3+对A位和B位的掺杂,明显提高了钛酸铋铁电陶瓷剩余极化强度,并且Bi4Ti3-xCexO12铁电陶瓷的介电损耗随温度的变化比一般的B位等电价离子取代的情形更加平缓.     

Pb(Sc_(1/2)Nb_(1/2))O_3-Pb(Mg_(1/3)Nb_(2/3))O_3-PbTiO_3-PbZrO_3陶瓷的介电、压电性能研究

为研究不同含量PbZrO_3(PZ)对Pb(Sc_(1/2)Nb_(1/2))O_3-Pb(Mg_(1/3)Nb_(2/3))O_3-PbTiO_3-PbZrO_3(PSN-PMN-PT-PZ)四元弛豫铁电陶瓷的影响,文中通过两步前躯体法制备位于准同型相界中的xPSN-yPMN-zPT-hPZ(x/y/z/h=6/60/33/1,5/58/34/3,5/55/35/5,5/53/35/7)四元弛豫铁电陶瓷.采用X射线衍射仪分析了所制备陶瓷的相结构,通过测定介电常数和温度之间的关系确定了陶瓷的相变温度,利用居里-外斯公式拟合了不同组分陶瓷的弥散相变特性.研究结果表明:所制备的陶瓷试样均为纯的钙钛矿结构.随着PZ含量的增加,PSNPMN-PT-PZ陶瓷居里温度Tc逐渐升高(134~160℃),介电常数降低,相变弥散度也增强;在所有组分中,0.05PSN-0.55PMN-0.35PT-0.05PZ组分表现出良好的综合性能,其居里温度Tc为151℃,压电常数d33为325pC·N-1,机电耦合系数kp为54.34%,最大介电常数εm为7 779,介电损耗tanδ为0.02.     

挠曲电效应对超薄铁电薄膜物理性能的调控

具有量子隧穿及阻变存储效应的超薄铁电薄膜引起了广泛的关注.在超薄铁电薄膜中,应变及应变梯度效应十分明显,因此由应变梯度所产生的挠曲电效应不可忽视.挠曲电效应是指应变梯度或非均匀应变场能局部地破坏反演对称,从而导致晶体产生电极化的效应.基于朗道热力学理论,建立了考虑挠曲电效应的超薄铁电薄膜相变的理论模型.通过该模型研究了挠曲电效应对纳米尺度超薄BaTiO3薄膜相变温度、铁电性能以及热释电系数的影响.研究结果表明:挠曲电效应提高铁电薄膜的电极化值和临界厚度,降低薄膜的相变温度.利用挠曲电效应可有效调控超薄铁电薄膜的相变温度及热释电系数.     

钙钛矿结构驰豫型铁电体的介电弛豫谱研究

通过分析钙钛矿结构驰豫铁电陶瓷铌镁酸沿的复介电响应,探讨了其在弥散相变温区的驰豫特征及极性微区、铁电微畴的极化机制。数值拟合表明幂指数Arrhenius关系比Vogel-Fulcher关系可更为合理地表征驰豫型铁电体。给出铁电微畴的驰豫响应时间分布函数,计算所得介电驰豫温度谱与实验结果吻合较好。     

强电流铁电陶瓷材料研究

强电流铁电陶瓷是一种组成结构为铁电相与反铁电相共存，而极化后为铁电相和亚铁电相的特种功能材料。该项目在四种材料中优选出一种缺位型新材料，采用等静电成型，极化前高温退火及高温极化工艺技术，制备了平行发射和垂直发射的铁电阴极样品，通过对电极边缘的绝缘保护处理增大了激励场强，提高了发射电流强度，通过SEM，XRD及晶胞参数测定等微观结构分析，验证了快速化反转引起电子发射机理的正确性，研究了结构缺陷，局部相变与电子发射特性的关系，为铁电阴极材料的开发应用提供了理论基础。     

Structure and Electric Properties of （1-x）（Bi1/2Na1/2） TiO3-xBaTiO3 Systems

The structural, dielectric and piezoelectric properties of （1-x）（Bi1/2Na1/2） TiO3-xBaTiO3 ceramics were investigated for the compositional range, x=0.02, 0.04, 0.06, 0.08, 0.10. The samples were synthesized by a conventional solid-state reaction technique. All compositions show a single perovskite structure, and X-ray powder diffraction patterns can be indexed using a rhombohedral structure. Lattice constants and lattice distortion increase while the amount of BaTiO3 increases. The X-ray diffraction results show the morphotropic phase boundary （MPB） of （1-x）（Bi1/2Na12） TiO3-xBaTiO3 exists in near x=0.06-0.08. Temperature dependence of dielectric constant eT33/ε0 measurement reveals that all compositions experience one structural phase and two ferroelectric phases transition below 400℃： rhombohedral （or rhombohedral plus tetragonal） ferroelectric phase ←→ tetragonal antiferroelectric phase ←→ tetragonal paraelectric phase. Relaxor behaviors exist in the course of ferroelectric to antiferroelectric phase transition. Dielectric and piezoelectric properties are enhanced in the MPB range for （ 1-x）（Bi1/2Na1/2）TiO3-xBaTiO3.     

Synthesis and Dielectric Properties of New Niobate BiTi3Nb7O30

A new niobate Ba5 BiTi3Nb7O30 was synthesized by the solid-state reaction. It was characterized by X-ray diffraction and dielectric constant measurements. The results show that Ba5BiTi3Nb7O30 is paraelectric at room temperature and belongs to tetragonal 4/ mmm symmetry with unit cell parameters a = 1.25020 nm, c =0.39704 nm. Ba5BiTi3Nb7O30 has only one phase transition, paraelectric to ferroelectric, below 0℃.     

Preparation, Characterization and Dielectric Property of Sr5 LaTi3 Nb7O30 Ceramic

Sr5LaTi3Nb7O30 ceramic was prepared by the conventional high temperature solid-state reaction route. The sintered samples were characterized by X-ray diffraction, scanning electron microscopy ( SEM ), differential thermal calorimetry ( DSC ) and dielectric measurements. The results show Sr5LaTi3Nb7O30 belongs to paraclectric phase of filled tetrngonal TB structure at room temperature, and undergoes a diffuse phase transition in the temperature range of -54-34℃ . And Sr5LaTi3Nb7O30 ceramic shows a high dielectric constant of 479 with a low dielectric loss of 0.005 at 1MHz . In comparison with Ba-based ceramics with TB structure, the temperature coefficients of the dielectric constant ( τt ) is significantly reduced.     

Synthesis and Dielectric Properties of New Niobate Ba_5BiTi_3Nb_7O_(30)

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Preparation and piezoelectric properties of CuO-added (Ag<Subscript>0.75</Subscript>Li<Subscript>0.1</Subscript>Na<Subscript>0.1</Subscript>K<Subscript>0.05</Subscript>)NbO<Subscript>3</Subscript> lead-free ceramics

CuO-doped (Ag_0.75Li_0.1Na_0.1K_0.05)NbO₃ (ALNKN-xCuO, x = 0–2mol%) lead-free piezoelectric ceramics were prepared by the solid-state reaction method in air atmosphere. The effects of CuO addition on the phase structure, microstructure, and piezoelectric properties of the ceramics were investigated. The experimental results show that the ALNKN ceramics without doping CuO possess rhombohedral phase along with K2Nb6O16-type phase and metallic silver phase. For all of the CuO-doped ALNKN ceramics, a pure perovskite structure with the orthorhombic phase was obtained by enclosing the samples in a corundum tube. A homogeneous microstructure with the grain size of about 1 μm was formed for the ceramics with 0.5mol% CuO. The grain size increases with increasing amount of CuO. The temperature dependence of dielectric properties indicates that the ferroelectric phase of the ALNKN-xCuO ceramics becomes less stable with the addition of CuO. The ceramics with x = 1mol% exhibit relatively good electrical properties along with a high Curie temperature. These results will provide a helpful guidance to preparing other AN-based ceramics by solid-state reaction method in air atmosphere.     

Microstructures and Electrical Properties of Bi_(0.5)-(Na_(1-x-y)K_xLi_y)_(0.5)TiO_3 Lead-free Piezoelectric Ceramics

The microstructures and electrical properties of Bi0.5(Na1-x-yKxLiy)0.5TiO3 lead-free piezoelectric ceramics were studied.These ceramics were prepared by conventional ceramic technique.XRD analysis reveals that the ceramics possess almost pure perovskite phase when y≤0.2.The SEM results show that,with more amounts of Li+,the crystalline grain growing speed is accelerated,and the sintering temperature can effectively be decreased.The measurements of piezoelectric properties indicate that the ceramics with relatively low amount of Li+ and high amount of K+ have comparatively large piezoelectricity.The dielectric measurements show that the ceramics have properties like relaxor ferroelectrics and diffuse phase transition(DPT) at Td and Tc,respectively.The results of ferroelectric measurements reveal the system has relatively higher remanent polarization Pr(27.6 μC/cm2) and lower coercive field Ec(37.5 kV/cm).     

Phase structure and electrical properties of La<Subscript>2</Subscript>O<Subscript>3</Subscript>-doped BiInO<Subscript>3</Subscript>-PbTiO<Subscript>3</Subscript> ceramics with high curie temperature

The phase structure and electrical properties of pure and La2O3-doped Bi-InO3-PbTiO3 （BI-PT） ceramics were studied respectively. In （1 -x）BI-xPT （x=0.72-0.80） ceramics, the stability of tetragonal phase increased with increasing x, and pure perovskite structure was obtained for x=-0.80 ceramics. The phase transition temperature range was between 575 ℃ and 600 ℃ for x=0.72-0.80 ceramics, higher than that of PT （-490 ℃）. The c/a ratio almost linearly decreased with increasing La2O3 content in x-0.80 ceramics. It is believed that Pb^2＋ vacancies were formed by La^3＋ substituting Pb^2＋ in La2O3-doped BI-PT ceramics. Tc shifted to lower temperature by 30 ℃/mol% La2O3. The maximum dielectric constant 8557 around 559 ℃ was exhibited in 0.5mol%-doped BI-0.80PT ceramics. La2O3-doped ceramics could be poled resulting from decreasing of c/a ratio and improving of dielectric loss and resistivity. The maximum piezoelectric coefficient d33 was 12 pC/N for 2mol%-doped BI-0.80PT ceramics.     

Preparation,structure and dielectric properties of tungsten bronze ferroelectrics in SrO-Eu<Subscript>2</Subscript>O<Subscript>3</Subscript>-TiO<Subscript>2</Subscript>-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> system

Compounds Sr4Eu2Ti4Nb6O30 and Sr5EuTi3Nb7O30 with filled tetragonal tungsten bronze structure were prepared,and the dielectric characteristics and ferroelectric transition were investigated.Both ceramics displayed weak frequency dependence in room temperature dielectric constant,which decreased from 125 to 118 for Sr4Eu2Ti4Nb6O30,from 206 to 195 for Sr5EuTi3Nb7O30 in the frequency range of 10 kHz to 1 MHz.The present ceramics showed a diffuse ferroelectric phase transition.The frequency independent transition temperature (Tm) indicated the above compounds had no relaxor property.The diffuseness (γ) was 1.45 and 1.64 for Sr4Eu2Ti4Nb6O30 and Sr5EuTi3Nb7O30 respectively.The weak ferroelectric of the present materials are indicated from the P-E hysteresis loops,and a small 2Pr of 0.596 μC/cm2 and 0.068 μC/cm2 were observed for Sr4Eu2Ti4Nb6O30 and Sr5EuTi3Nb7O30 respectively.     

简立方晶格的反铁电模型及其序参量

从相互作用能的角度分析，得出了简立方晶格可能具有的两种反铁电模型A，B，对于模型A，序参量为三阶全对称的张量П，所属对称群为D2d，模型B的序参量为轴矢R^→，所属对称群为C2i。这两种模型顺电相所属点群显然均为Oh，按居里原理，所选取的序参量能很好地说明相变前后对称性的变化，进一步证明了用R^→，П做反铁电相变序参量的合理性。     

Dielectric properties of Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> ceramics by impedance spectroscopic method

Various lead-free ceramics have been investigated in search for new high-temperature dielectrics. In particular, Bi₄Ti₃O₁₂ is a type of ferroelectric ceramics, which is supposed to replace leadcontaining ceramics for its outstanding dielectric properties in the near future. Ferroelectric ceramics of Bi₄Ti₃O₁₂ made by conventional mixed oxide route have been studied by impedance spectroscopy in a wide range of temperature. X-ray diffraction patterns show that Bi₄Ti₃O₁₂ ceramics are a single-phase of ferroelectric Bi-layered perovskite structure whether it is calcined at 800 °C or after sintering production. This study focused on the effect of the grain size on the electric properties of BIT ceramics. The BIT ceramics with different grain sizes were prepared at different sintering temperatures. Grain becomes coarser with the sintering temperature increasing by 50 °C, relative permittivity and dielectric loss also change a lot. When sintered at 1 100 °C, r values peak can reach 205.40 at a frequency of 100 kHz, the minimum dielectric losses of four different frequencies make no difference, all close to 0.027. The values of E _a range from 0.52 to 0.68 eV. The dielectric properties of the sample sintered at 1 100 °C are relatively better than those of the other samples by analyzing the relationship of the grain, the internal stresses, the homogeneity and the dielectric properties. SEM can better explain the results of the dielectric spectrum at different sintering temperatures. The results show that Bi₄Ti₃O₁₂ ceramics are a kind of dielectrics. Thus, Bi₄Ti₃O₁₂ can be used in high-temperature capacitors and microwave ceramics.