Analytical modeling of the apparent d33 piezoelectric coefficient determined by the direct quasistatic method for different boundary conditions.

The longitudinal piezoelectric coefficient d33 measured by the quasistatic (Berlincourt-type) method is strongly dependent on the sample aspect ratio (thickness/lateral dimension) and the type of contacts used to collect the charge and apply the pressure on the sample. In this study, we present an analytical model in which apparent (measured) d33 is a function of the aspect ratio, the mechanical properties of contacts, and the properties of piezoelectric material. Using derived relations, it is possible to obtain the true value of d33 in the wide range of boundary conditions. The analytical results are compared with simulations using finite element modeling (FEM) and with experimental data; and good correlation is found among them. Effect of the geometry of the contacts on apparent d33 value is specifically addressed.     

The effect of boundary conditions and sample aspect ratio on apparent d33 piezoelectric coefficient determined by direct quasistatic method

The effect of boundary conditions (e.g., type of metal contacts) and sample geometry (e.g., sample aspect ratio) on measurements of direct longitudinal d33 coefficient in piezoelectric ceramics is studied by direct quasistatic method. We show that at small aspect ratio (thickness/lateral dimension <0.1) the measured d33meas is as much as 30% lower than the true value, d33true. Measured d33 increases with increasing aspect ratio and reaches its true value at a threshold aspect ratio that is dependent on ceramic composition and is about approximately 0.5 in the case of soft and hard Pb(Zr,Ti)O3. Experimental results show that, when the force is applied over the whole electroded surface of the sample, the d33 depends only on the aspect ratio and not size of samples. The experimental results are compared with simulations using finite element modeling (FEM) and are interpreted in terms of distribution of strain/stress within the sample, which leads to functional dependence of the measured d33 on transverse d31 and shear d15 coefficients. It is shown experimentally and by FEM that the value of d33 at low aspect ratios depends on the type of metallic contacts used to collect the charge and apply the pressure on the sample. Effect of nonlinearity of the d31 and d15 coefficients on d33 measurements also is considered.     

Anisotropy in domain engineered 0.92Pb(Zn1/3 Nb2/3)O3-0.08PbTiO3 single crystal and analysis of its property fluctuations

The orientation dependence of slowness and electromechanical coupling coefficients of 0.92Pb(Zn/sub 1/3/Nb/sub 2/3/)O/sub 3/-0.08PbTiO/sub 3/ (PZN-8%PT) domain engineered single crystal was analyzed based on the measured complete set of elastic, piezoelectric, and dielectric constants. There exist one quasi-longitudinal, one quasi-shear, and one pure shear wave in each of the [100]-[010], [010]-[001], and [001]-[110] planes. The slowness of the quasi-shear wave exhibits strong anisotropy in all three planes, and the coupling coefficient k/sub 33/ and k/sub 31/ reach their maximum in [001] and [110] directions of cubic axis, respectively. Because the composition of the PMN-8%PT system is very close to the morphotropic phase boundary, the extraordinary large piezoelectric coefficients d/sub 31/ and d/sub 33/, and high coupling coefficient k/sub 33/ are very sensitive to compositional variation. We have performed error analysis and proposed an improved characterization scheme to derive a complete data set with best consistency.     

Mg/sub x/Zn/sub 1-x/O: a new piezoelectric material

Piezoelectric ZnO thin films have been successfully used for multilayer surface acoustic wave (SAW) and bulk acoustic wave (BAW) devices. Magnesium zinc oxide (Mg/sub x/Zn/sub 1-x/O) is a new piezoelectric material, which is formed by alloying ZnO and MgO. Mg/sub x/Zn/sub 1-x/O allows for flexibility in thin film SAW device design, as its piezoelectric properties can be tailored by controlling the Mg composition, as well as by using Mg/sub x/Zn/sub 1-x/O/ZnO multilayer structures. We report the metal-organic chemical vapor deposition (MOCVD) growth, structural characterization and SAW evaluation of piezoelectric Mg/sub x/Zn/sub 1-x/O (x<0.35) thin films grown on (011~2) r-plane sapphire substrates. The primary axis of symmetry, the c-axis, lies on the Mg/sub x/Zn/sub 1-x/O growth plane, resulting in the in-plane anisotropy of piezoelectric properties. SAW test devices for Rayleigh and Love wave modes, propagating parallel and perpendicular to the c-axis, were designed and fabricated. Their SAW properties, including velocity dispersion and piezoelectric coupling, were characterized. It has been found that the acoustic velocity increases, whereas the piezoelectric coupling decreases with increasing Mg composition in piezoelectric Mg/sub x/Zn/sub 1-x/O films.     

Determination of complex coefficients of radially polarized piezoelectric ceramic cylindrical shells using thin shell theory

A method is presented to determine the complex coefficients E/sub 33//sup T/, s/sub 11//sup E/, s/sub 12//sup E/, and d/sub 31/ of piezoelectric materials. The real parts of these coefficients are determined using axially polarized thin discs in the ANSI/IEEE Standard but are determined here using radially polarized cylindrical shells. The coefficients are determined by iteratively refining them until the values of the low-frequency complex admittance, three resonance frequencies, and three band-widths computed using a thin-shell analytical model and the coefficients are very nearly equal to measured values. The accuracy of the method is determined by using quantities computed using a finite-element model in place of measured values. Measurement errors are accounted for by using a resolution of 10 Hz to compute the critical frequencies. The differences between the coefficients input to the finite-element model and those obtained using the iteration method are the errors. It is shown that the method is sufficiently accurate to use thin radially polarized cylindrical shells to determine the properties of new materials as well as characterize those used in hydrophones or other devices.     

NbO3-LiNbO3无铅压电陶瓷的烧结特性和压电性能研究

采用传统陶瓷烧结工艺制备了（1-x）（K0．5Na0．5）NbO3-xLiNbO3无铅压电陶瓷，研究了陶瓷的结构、烧结特性及电性能特征．制备的（K0．5Na0．5）NbO3-LiNbO3陶瓷为单一的钙钦矿结构，室温下其相结构随LiNbO3含量增加逐渐由正交相向四方相转变，显微结构也由于LiNbO3含量的不同而表现出很大差异．与（K0．5Na0．5）NbO3陶瓷相比，（K0．5Na0．5）NbO3-LiNbO3陶瓷的烧结温度降低，烧结特性得到改善．（K0．5Na0．5）NbO3-LiNbO3陶瓷表现出优越的压电性能，其中0．94（K0．5Na0．5）NbO3—0．06LiNbO3（x=0．06）陶瓷的压电常数d33达到205pC／N，机电耦合系数kp为40．3％，kt达到49．8％．     

PZT陶瓷/橡胶复合材料的压电性能

用PZT压电陶瓷粉末分散在无压电性的橡胶基体中制成压电复合材料。通过压电常数和介电常数测定、扫描电镜、介电谱等手段研究了有关因素对复合材料压电性能的影响。结果表明,复合材料的压电常数d₃₃随PZT体积含量φ和橡胶介电常数ε₁的增加而增大,随PZT介电常数ε₂的增加而减小,符合理论式 d₃₃=15φε₁d₃₃/(1-φ)(2+3φ)ε₂ 橡胶基体的极性基团、极性链节和交联健偶极的转向极化及分子链的柔性对复合材料的极化和压电常数有重要影响。橡胶的极性越大及分子链的柔性越高,则复合材料的压电常数d₃₃越高。      

Measurements along the growth direction of PMN-PT crystals: dielectric, piezoelectric, and elastic properties

Property measurements are reported for Pb(Mg1/3Nb2/3)03-PbTiO3 (PMN-PT) single crystals grown along (001) by a seeded-melt method. Chemical segregation occurs during crystal growth, leading to property changes along the growth direction. Variations in dielectric, piezoelectric, and elastic properties were evaluated for specimens selected from the crystals. Room-temperature data are correlated with Tc and composition that ranged from 27 to 32% PT, i.e., in the vicinity of the morphotropic phase boundary (MPB). While there was little change in the high electromechanical coupling factor k33 (0.87-0.92), both the piezoelectric charge coefficient d33 (1100-1800 pC/N) and the free dielectric constant K3 (4400-7000) were found to vary significantly with position. Increases in d33 and KT33 were relatively offsetting in that the ratio yielded a relatively stable piezoelectric voltage coefficient g33 (27-31 x 10(-3) Vm/N). Values are also reported for the elastic compliance (3.3-6.3 x 10(-11) m2/N) determined from resonance measurements. Enhancements in d33 and K(T)33 were associated with lattice softening (increasing sE33) as the composition approached the MPB. Details are reported for the piezoelectric, dielectric, and elastic properties as a function of growth direction, Tc, and composition. The results are useful for an understanding of properties in PMN-PT crystals and for the design of piezoelectric devices.     

Phase-transition temperatures and piezoelectric properties of (Bi1/2Na1/2)TiO3-(Bi1/2Li1/2)TiO3-(Bi1/2K1/2)TiO3 lead-free ferroelectric ceramics.

The phase-transition temperatures and piezoelectric properties of x(Bi(1/2)Na(1/2))TiO3-y(Bi(1/2)Li(1/2))TiO3-z(Bi(1/2)K(1/2))TiO3 [x + y + z = 1] (abbreviated as BNLKT100(y)-100(z)) ceramics were investigated. These ceramics were prepared using a conventional ceramic fabrication process. The phase-transition temperatures such as depolarization temperatures T(d), rhombohedraltetragonal phase transition temperature T(R-T), and dielectric-maximum temperature T(m) were determined using electrical measurements such as dielectric and piezoelectric properties. The X-ray powder diffraction patterns of BNLKT100(y)-100(z)) show the morphotropic phase boundary (MPB) between rhombohedral and tetragonal at approximately z = 0.20, and the piezoelectric properties show the maximum at the MPB. The electromechanical coupling factor k(33), piezoelectric constant d(33) and T(d) of BNLKT4-20 and BNLKT8-20 were 0.603, 176 pC/N, and 171 degrees C, and 0.590, 190 pC/N, and 115 degrees C, respectively. In addition, the relationship between d33 and Td of tetragonal side and rhombohedral side for BNLKT4-100z and BNLKT8-100z were presented. Considering both high Td and high d(33), the tetragonal side of BNLKT4-100z is thought to be the superior composition. The d(33) and T(d) of BNLKT4-28 were 135 pC/N and 218 degrees C, respectively. Moreover, this study revealed that the variation of T(d) is related to the variation of lattice distortion such as rhombohedrality 90-alpha and tetragonality c/a.     

Elastic and piezoelectric properties of La3Ga5SiO14 and La3Ga5.5Ta0.5O14: an application of resonant ultrasound spectroscopy

The electromechanical properties of La/sub 3/Ga/sub 5/SiO/sub 14/ (LGS) and La/sub 3/Ga/sub 5.5/Ta/sub 0.5/O/sub 14/ (LGT) have been studied at room temperature on 25 samples using resonant ultrasound spectroscopy (RUS). The RUS method facilitates simultaneous determination of all independent elastic and piezoelectric constants of a sample within the same frequency range and yields sample parameters with high internal consistency. Consequently, the spread of the experimental results presented here is significantly lower than the scatter of literature data obtained by different experimental techniques.     

Optimization of single-gate carbon-nanotube field-effect transistors

The performance of Schottky-barrier carbon-nanotube field-effect transistors (CNTFETs) critically depends on the device geometry. Asymmetric gate contacts, the drain and source contact thickness, and inhomogenous dielectrics above and below the nanotube influence the device operation. An optimizer has been used to extract geometries with steep subthreshold slope and high I/sub on//I/sub off/ ratio. It is found that the best performance improvements can be achieved using asymmetric gates centered above the source contact, where the optimum position and length of the gate contact varies with the oxide thickness. The main advantages of geometries with asymmetric gate contacts are the increased I/sub on//I/sub off/ ratio and the fact that the gate voltage required to attain minimum drain current is shifted toward zero, whereas symmetric geometries require V/sub g/=V/sub d//2. Our results suggest that the subthreshold slope of single-gate CNTFETs scales linearly with the gate-oxide thickness and can be reduced by a factor of two reaching a value below 100 mV/dec for devices with oxide thicknesses smaller than 5 nm by geometry optimization.     

造孔剂含量对多孔BiScO3-PbTiO3高温压电陶瓷性能的影响

为研究造孔剂含量对多孔BiScO_3-PbTiO_3(记作BS-PT)高温压电陶瓷性能的影响,采用炭黑作为造孔剂,通过传统固相烧结法对不同初始固相体积分数的准同型相界附近的BS-PT/炭黑混合物制备出多孔高温压电陶瓷.利用X射线衍射仪对多孔陶瓷进行物相分析,通过扫描电子显微镜观察样品的新鲜断面和抛光热腐蚀后的表面显微结构,并对其压电、介电和水声性能进行研究.结果表明:制备的不同初始BS-PT体积分数多孔压电陶瓷均为立方钙钛矿相结构,孔隙通道密实化清晰可见,没有显著的缺陷,气孔的形状是长条形的,长度从几微米到几十甚至上百微米不一,气孔之间是孤立的;随着造孔剂炭黑的体积分数从20%增加至50%,气孔率线性地从8.3%增加至22.1%,εr、d33及d31逐渐下降,静水压优值(HFOM)逐渐增大.多孔压电陶瓷的性能强烈依赖于孔隙空间结构,如气孔率、孔径、孔隙形态及连接方式.     

Mn改性Na0.5Bi2.5Nb2O9高温压电陶瓷的研究

采用固相法获得了Mn改性的Na0.5Bi2.5Nb2O9(NBN+xmol%MnCO3,0≤x≤10.0)铋层状压电陶瓷,并系统地研究了Mn(掺杂)对NBN基陶瓷显微结构与电性能的影响.结果表明,所有获得的样品都是居里点在700℃以上的单一相铁电体.加入Mn显著地提高了NBN系列陶瓷的机械品质因素Qm,明显改善了陶瓷的压电与机电性能.当MnCO3掺杂量为8.0mol%时,陶瓷获得最佳电性能:tanδ=0.749%,d33=20 pC/N,Qm=3120,kp=12.37%,kt=21.09%,Pr=7.01μC/cm2.NBN+xmol%MnCO3(x=8.0)陶瓷经700℃退极化处理后,其d33保持为原来的75%(~15 pC/N),表明该材料在高温领域下具有良好的应用前景.     

Pb(Mn1/3Sb2/3)0.05Zr0.47Ti0.48O3压电陶瓷的温度稳定性研究

探讨了硬性添加物MnO2、软性添加物Nb2O5和两性添加物Cr2O3对锑锰锆钛酸铅Pb(Mn1/3Sb2/3)0.05Zr0.47Ti0.48O3(简称PMSZT5)压电陶瓷的相组成及温度稳定性的影响.研究结果发现:各掺杂组成在900℃的煅烧温度下,都可以得到钙钛矿结构.随着各掺杂离子的增大,四方相含量减少,准同型相界向三方相移动.综合考虑离子掺杂对PMSZT5压电陶瓷的机电性能及温度稳定性的研究结果表明:锰过量较其它铌和铬掺杂的温度稳定性更好,机电性能最佳的PMSZT5+0.1wt%MnO2的组成,ε33T/ε0=1560,d33=350pC/N,Kp=0.63,25~80℃的fr、K31和d31平均温度系数分别为72×10-6/℃、0.027%/℃和0.100%/℃.     

Temperature behavior of dielectric and piezoelectric properties of samarium-doped lead titanate ceramics

The dielectric and electromechanical coupling properties of Sm-doped and Mn-doped PbTiO(3) ceramics were investigated from 4.2 to 300 K. The upper and lower limits of the ceramic dielectric and piezoelectric properties were calculated by averaging the single-domain constants that were determined from a phenomenological theory. Comparisons of the measured and calculated properties were then made. The measured dielectric permittivity epsilon(T)(33) and piezoelectric strain coefficient d(33) appear to be mainly due to the averaging of the intrinsic single-domain response. The large piezoelectric and electromechanical anisotropies present in modified PbTiO(3) ceramics also appear to be an intrinsic property of the material. The piezoelectric coefficient d(31), as well as the planar coupling coefficient k(p), was found to have very small values over two temperature regions, from 120 to 170 K and from 240 to 270 K.     

钛酸铅-环氧树脂压电复合材料的制备

为了制备高体积填充率的钛酸铅－环氧压电复合材料，本文采用了将环氧树脂的丙酮稀溶液与钛酸铅细粉混合再抽真空除去溶剂的方法，这样有利于环氧树脂与钛酸铅进行良好的、均匀的复合，大大减少了界面气孔，所制得的复合材料钛酸铅填充率高（体积填充率达７０％），复合材料表面光滑无宏观缺陷。压电性能测定结果表明：极化条件不同，ｄ３３的值也不同，介电常数ε３３均为４３。，样品能够达到稳定极化的最佳ｇ３３的值为：２３．１×１０－３Ｖ·ｍ·Ｎ－１。     

Comprehensive characterization of PVDF-TrFE thin films for microelectromechanical system applications

This paper presents a comprehensive characterization of a polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) thin film with 75/25 molar ratio for piezoelectric MEMS applications. PVDF-TrFE film was deposited on a silicon substrate using spin coating, and electrodes were formed using sputtering. Dielectric constant and dielectric loss factor were measured at different frequencies. Frequency and temperature dependence of the ferroelectric response was examined to investigate required poling conditions and maximum operating temperature. The lower limit for the coercive field was measured as 55 V/μm at room temperature. Coercive field decreased with temperature with a slope of ?0.1 V/μm K, and ferroelectric to paraelectric transition occurred between 100? and 108?°C. Piezoelectric displacement measurements were performed using an atomic force microscope based method. Average value of the effective piezoelectric d₃₃ coefficient was measured as ?23.9 pm/V. No degradation was observed in this value after 2?×?10⁵ unipolar excitation cycles. On the other hand, significant fatigue was observed in the piezoelectric response due to polarization switching; 1.8?×?10⁵ cycles caused an average reduction of 33% in the effective d₃₃. Presented data corroborates with the previous studies in the literature and can be used in the design of PVDF-TrFE based MEMS devices utilizing its dielectric, ferroelectric, and piezoelectric properties.     

Ni/Au、Pd/Au与p-AlGaN材料的接触特性

在AlGaNpin型日盲紫外探测器结构中的p-AlGaN层上生长了Ni/Au和Pd/Au,并在600～850℃温度下进行快速热退火,测量其退火前后传输线模型中各金属接触间的电学性质。实验发现,Ni/Au与Pd/Au在p-AlGaN上表现出了不同的接触性能。为了更好的说明金属与p-AlGaN材料接触之间在退火后电流的变化,还测量了p-AlGaN材料裸片两点之间I-V曲线在退火前后的变化。实验表明,比起Ni/Au来,Pd/Au在p-AlGaN材料上制备欧姆接触具有一定的优势,并在文中进行了分析。     

1-3型水泥基压电复合材料的制备及性能

采用切割-浇注法, 以硫铝酸盐水泥为基体, 制备了1-3型水泥基压电复合材料。详细阐述了1-3型水泥基压电复合材料的制备过程; 研究了0.375Pb(Mg_1/3Nb_2/3)O₃-0.375PbTiO₃-0.25PbZrO₃压电陶瓷柱的宽厚比w/t对1-3型水泥基压电复合材料的压电性能、 介电性能和声阻抗的影响。结果表明: 压电陶瓷柱的宽厚比w/t对1-3型水泥基压电复合材料性能有很大影响, 随着w/t的增加, 其压电应变常数d₃₃、 机电耦合系数K_p与K_t、 机械品质因数Q_m、 介电常数ε_r和介电损耗tanδ均随着w/t的增加而减小, 而压电电压常数g₃₃值几乎不受w/t的影响。在压电陶瓷体积分数仅为22.72%的条件下, 调节压电陶瓷柱的宽厚比w/t至0.130, 可使复合材料的声阻抗与混凝土的声阻抗十分接近, 从而有效地解决了智能材料在土木工程中的声阻抗相容性问题。      

PMNT陶瓷材料的压电介电性能研究

本文研究了准同型相界处铌镁酸铅－钛酸铅陶瓷材料的介电压电性能,合适的组份和烧结,可使ＰＭＮＴ陶瓷材料具有较好的压电性能,ｄ３３达５４０ｐＣ／ＮＭ,ｋｔ达０．５０以上,观察了不同烧结工艺下陶瓷材料的微观结构,烧结时间过长不仅使晶粒尺寸变大,亦可造成晶粒快速生长,对化学组成和微观结构与压电性能的关系进行了讨论。