Magnetoelectric Effect in Composites of Magnetostrictive and Piezoelectric Materials

In the past few decades, extensive research has been conducted on the magnetoelectric (ME) effect in single phase and composite materials. Dielectric polarization of a material under a magnetic field or an induced magnetization under an electric field requires the simultaneous presence of long-range ordering of magnetic moments and electric dipoles. Single phase materials suffer from the drawback that the ME effect is considerably weak even at low temperatures, limiting their applicability in practical devices. Better alternatives are ME composites that have large magnitudes of the ME voltage coefficient. The composites exploit the product property of the materials. The ME effect can be realized using composites consisting of individual piezomagnetic and piezoelectric phases or individual magnetostrictive and piezoelectric phases. In the past few years, our group has done extensive research on ME materials for magnetic field sensing applications and current measurement probes for high-power electric transmission systems. In this review article, we mainly emphasize our investigations of ME particulate composites and laminate composites and summarize the important results. The data reported in the literature are also compared for clarity. Based on these results, we establish the fact that magnetoelectric laminate composites (MLCs) made from the giant magnetostrictive material, Terfenol-D, and relaxor-based piezocrystals are far superior to the other contenders. The large ME voltage coefficient in MLCs was obtained because of the high piezoelectric voltage coefficient of the piezocrystals and large elastic compliances. In addition, an optimized thickness ratio between the piezoelectric and magnetostrictive phases and the direction of the magnetostriction also influence the magnitude of the ME coefficient.     

Dielectric and Pyroelectric Properties of Lead Zirconate Titanate Composite Films

A new sol-gel approach has been established to prepare dense and crack-free lead zirconate titanate (PZT)/PZT composite films. This new process combines the modified sol-gel method for preparing ceramic/ceramic composite films and the infiltration technique. In the modified sol-gel method, sintered PZT powder is dispersed in a PZT precursor solution to form a slurry which is then spin-coated on a substrate. However, the resulting composite film usually contains a considerable amount of pores, and thus resulting in serious degradation of the mechanical, ferroelectric and piezoelectric properties of the films. In the present work, an additional step, infiltration, has been included in the method. A diluted PZT precursor solution is deposited on the composite film to infiltrate and fill-up the pores, and hence a dense composite film is obtained. The dielectric, ferroelectric and pyroelectric properties of the resulting PZT/PZT composite film are comparable to those of a sol-gel derived PZT film; showing the values of 1200, 0.04, 21 μC/cm² and 180 μC/m² K for relative permittivity, dielectric loss, remanent polarization and pyroelectric coefficient, respectively.     

Dielectric Properties of Niobium and Lanthanum Doped Lead Barium Zirconate Titanate Relaxor Ferroelectrics

The lead barium zirconate titanate (PBZT) relaxor ferroelectrics are ideal for high voltage capacitor applications due to their high dielectric constant, stability under DC bias, and temperature stability. In this study the composition (Pb_0.65Ba_0.35)(Zr_0.70Ti_0.30)O₃ was selected as the base composition. It exhibited typical relaxor characteristics such as frequency dispersion and diffuse phase transition. The dielectric constant is 6000 at room temperature and remains almost constant under electric field as high as 20 kV/cm. To further enhance the dielectric properties, various amounts of niobium oxide and lanthanum oxide dopants were added to the base PBZT to alter the defect structure and hence the dielectric properties. It was found that the dielectric constant of 1% Nb-doped samples was increased by 20–25% while maintaining similar voltage stability. This increase was attributed to the abnormal grain growth in the Nb-doped sample, and the correlation between microstructure and dielectric constant was drawn through a grain size study. The La addition only caused a monotonic decrease of dielectric constant and slightly improved voltage stability.     

Elastic Properties of Barium Zirconate Titanate Ceramics

In the paper the influence of zirconium admixture on the structure and material constants of polycrystalline ferroelectric materials BaZr_xTi_1-xO₃ (BZT) was examined. The barium zirconate titanate samples were prepared by a conventional solid state reaction method. A single phase with perovskite structure of the samples, was identified by an X-Ray diffraction technique at room temperature. The performed EDS study revealed that the samples were perfectly sintered and the material was chemically homogeneous. The dependence of shear modulus G on sample composition is similar to the respective dependence of Young's modulus E, whereas the Poisson's ratio ν decreases with the increase in zirconium concentration.     

磁致伸缩、压电层状复合磁电传感器非线性动态有限元模型

基于磁致伸缩材料标准平方模型和压电材料线性本构关系,应用Hamilton变分原理建立了磁电传感器的磁-机-电耦合特性的动力学方程。建立的动力学方程考虑了磁致伸缩材料的磁滞现象和E效应的影响。应用所建立的模型求解了LT型磁致伸缩/压电磁电传感器的输出特性,与实验结果进行对比发现模型可较准确地预测磁电传感器在不同偏置磁场和交流驱动磁场激励下其输出电压随时间的变化关系。当偏置磁场为22.1kA/m,正弦交流驱动磁场为7.4kA/m、频率为100Hz时,计算结果和实验结果误差为0.9%。同时,应用该模型还可以确定磁电传感器的最大交流驱动磁场。     

Lead Zirconate Titanate Film Formation Technology with Use of Spray Coating Method

This paper presents a three-dimensional microfabrication and integration technology for MEMS smart materials that utilizes a spray coating method. Spray coating is shown to be most effective for additional deposition on non-planar surfaces. PZT films were formed both on flat and uneven surfaces at a thickness of about 1μ m. Perovskite structures were formed with suitable heat treatment and ferroelectric P-E hysteresis loop was also obtained. This paper is the first report from our group and other researchers on the deposition of smart materials for MEMS using a spray coating method. Spray coating has been proposed as an effective three-dimensional coating method which can be used to deposit piezoelectrics, pyroelectrics, magnetics, etc. for sensors and actuators. The hydrophilic and hydrophobic properties between the substrate surface and ejected liquid are most essential process factors in the spray coating method for improving the film growth conditions.     

Effect of Zr/Ti Ratio on Microstructure and Electrical Properties of Lead Zirconate Titanate Thin Films Derived by Pulsed Laser Deposition

PZT films were fabricated using various targets of Pb(Zr_xTi_{1 – x})O₃ with Zr/Ti ratios of 70/30, 58/42, 52/48, 45/55 and 30/70, and with excess PbO of 20 wt% on Pt/Ti/SiO₂/Si(100) substrates. The rosette structure was observed in the films derived from the target with a Zr/Ti ratio of 70/30 and disappeared with increasing titanium composition. The observations on surface and cross-sectional microstructure were consistent with a higher perovskite nucleation for the higher Ti content films. The PZT films derived from the target with a Zr/Ti ratio of 45/55 had a polycrystalline columnar microstructure extending throughout the thickness of the film and no pyrochlore phase on the surface was observed. The PZT films derived from the target with a Zr/Ti ratio of 45/55 exhibited better electric properties than those derived from the target with a Zr/Ti ratio of 52/48.     

Dielectric Characteristics of In-Plane Polarized Lead Zirconate Titanate Thin Films on Oxide Layers

Sol-gel derived lead zirconate titanate (PZT) films have been prepared on STO-passivated silicon substrates. The STO buffer layer of thickness about 55 nm is prepared by rf-magnetron sputtering. XRD results reveal that the PZT film has well-crystallized perovskite phase, indicating that the thin STO layer can effectively prevent reaction and inter-diffusion between the PZT film and silicon substrate. Interdigitated electrodes (IDEs) have then been deposited on the PZT film by magnetron sputtering and patterned using the standard photolithography. With the IDEs, the dielectric and ferroelectric properties of the PZT film under transverse or in-plane electric fields have been investigated. By assuming a uniform distribution of electric field (in-plane electric field model), the estimated relative permittivity of the PZT film is about 2100, while the dielectric loss is less than 1%. Good in-plane polarization hysteresis loop is observed, showing an observed remanent polarization value of 21 μC/cm², which is comparable to that of a PZT film with both top and bottom electrodes. The in-plane polarized PZT/STO/SiO₂/Si film can be used to fabricate d₃₃-mode unimorph bending transducers, which will have much better performance than the conventional bending transducers driven electromechanically through the piezoelectric d₃₁ mode.     

Design and Fabrication of a Lead Zirconate Titanate (PZT) Thin Film Acoustic Sensor

Piezoelectric MEMS acoustic sensors have potential applications in a wide variety of applications including hearing aids, surveillance, heart monitoring, etc. For each of these systems and many others, the acoustic sensors must be miniaturized and have low power requirements. A piezoelectric based microphone can provide a solution to these requirements, as they offer the ability to passively sense without the power requirements of condenser or piezoresistive microphone counterparts. This research effort reports on the design and fabrication of a piezoelectric PZT based acoustic sensor. A circular clamped membrane consisting of a dielectric for structural support and a piezoelectric actuator has been fabricated on a silicon wafer using silicon deep reactive ion etching (DRIE). Sensors ranging from 500–2000 microns in diameter have been fabricated and characterized using scanning laser Doppler vibrometry and calibrated acoustic tone sources. The PZT sensors exhibited a sensitivity of 97.9–920 nV/Pa depending on geometry.     

Studies on Electrical Properties and Magnetoelectric Effect of (x)Ni0.8Cu0.2Fe2O4 + (1?x)Ba0.8Pb0.2Ti0.8Zr0.2O3 Composites

Materials consisting of piezomagnetic and piezoelectric phases viz. Ni_0.8Cu_0.2Fe₂O₄ and Ba_0.8Pb_0.2 Ti_0.8Zr_0.2O₃ have been prepared by standard ceramic method. The presence of two phases in the composites has been confirmed by XRD. Variation of the dielectric constant with frequency in the range 100–1 MHz has been studied at room temperature and the variation of dielectric constant with temperature at set frequencies (1 kHz, 10 kHz, 100 kHz and 1 MHz) has been studied. The dielectric relaxation was observed for the compositions with tetragonal structure whereas normal behaviour was observed for cubic structure. All the samples have shown linear magnetoelectric conversion in the presence of a static magnetic field. The dc resistivity (ρ_DC) was studied as a function of temperature in the range 300–773^∘K. The variation of resistivity with temperature shows metal/seconductor behaviour.     

Dielectric Behavior and Magnetoelectric Effect in Ni0.75Co0.25Fe2O4 + Ba0.8Pb0.2TiO3 ME Composites

Magnetoelectric composites with ferrite + ferroelectric compositions xBa_0.8Pb_0.2TiO₃ + (1 – x) Ni_0.75Co_0.25Fe₂O₄ in which x varies as 0, 0.55, 0.70, 0.85 and 1.0 were prepared by ceramic method. X-ray analysis confirms single-phase formation in x = 0 and x = 1 compositions, whereas the presence of both phases is shown in x = 0.55, 0.70 and 0.85 compositions. Variation of dielectric constant () with temperature and frequency has been studied. All the samples have show linear magnetoelectric conversion in the presence of static magnetic field. Static magnetoelectric conversion factor, (dE/dH), was measured as a function of magnetic field in the samples with x = 0.55, 0.70 and 0.85 compositions. The maximum value of dE/dH was found to be 140 V/cm/Oe for x = 0.85 composition.     

Electrical Properties of Bismuth Titanate Based Ceramics with Secondary Phases

Bi₄Ti₃O₁₂ (BIT) based ceramics were prepared by hydroxide coprecipitation method and subsequent treatment at 650C for 1 h. Calcined BIT was doped with different amounts of WO₃ by surface doping using W(C₂H₅O)₆. The amount of dopant modified the sintering behaviour of BIT-based ceramics through a liquid-phase assisted sintering mechanism in the case of low dopant concentration and Zenner effect when high concentration of dopant was used. Consequently, the microstructure and the electrical properties were strongly dependent on the dopant concentration. Doped BIT-based ceramics showed a microstructure composed of very small platelet-like grains and the electrical conductivity was markedly decreased. The high electrical resistivity makes possible the polarization of doped ceramics and relatively good piezoelectric parameters were measured.     

AF9M1对KNN基陶瓷的结构与压电性能的影响

采用传统固相烧结法制备了K0.5Na0.5Nb O3-x Al(Fe0.9Mn0.1)O3(KNN-AF9M1)无铅压电陶瓷,着重研究了AF9M1的不同掺杂量(x分别为0,0.02,0.04,0.06,0.08)对陶瓷显微结构和压电性能的影响。结果表明,室温下,少量AF9M1的掺杂并未改变KNN基陶瓷正交相钙钛矿结构,但有助于陶瓷晶粒的生长及致密化。随着AF9M1含量的增加,陶瓷的压电常数(d33)、机电耦合系数(kp)、机械品质因数(Qm)和居里点(Tc)均先增大后减小,当x=0.04时,均达到最大值,分别为121 p C/N、0.35、179和392℃。     

Nonlinear magneto-electric response of giant magnetostrictive-piezoelectric composite sensors in harmonic and stochastic excitation

Nonlinear magneto-electric response characteristics of giant magnetostrictive-piezoelectric composite sensors in harmonic and stochastic magnetic fields are studied in this paper. Van der Pol nonlinear differential items are introduced to explain the hysteresis phenomena of both giant magnetostrictive material and piezoelectric ceramics. The nonlinear dynamic model of giant magnetostrictive-piezoelectric composite sensors in harmonic and stochastic magnetic fields is developed. The expression of dynamic response of the system is obtained, and the bifurcation characteristics of the system are analyzed. The results of this paper are helpful for optimal design and improvement of giant magnetostrictive-piezoelectric composite sensors.     

Bi0.5(Na0.82-xK0.18Lix)0.5TiO3无铅压电陶瓷的微结构与电性能

采用传统陶瓷制备工艺制备了[Bi0.5(Na0.82-xK0.18Lix)0.5]TiO3(x=0.01~0.07)无铅压电陶瓷.研究了该体系陶瓷的微结构以及应力对平面机电耦合系数kp和压电常数d33的影响.结果表明,[Bi0.5(Na0.82-xK0.18Lix)0.5]TiO3无铅压电陶瓷具有单一钙钛矿结构,Li+有抑制晶粒长大的作用.当x=0.03时,压电陶瓷样品表现出优良的压电性能:压电常数d33和平面机电耦合系数kp分别为154 pC/N和0.296.同时发现,退火可消除内应力,有利于提高d33,但会使kp减小;极化会引起介电常数εr减小,电畴转向过程中产生的应力对d33影响较为明显     

无铅压电陶瓷的研究现状与发展趋势

随着人们环保意识的增强,无铅压电陶瓷的研究和开发成为当前压电材料领域研究的热点。本文综述了无铅压电陶瓷研究开发的相关进展,重点介绍了BaTiO3基、Bi1/2Na1/2TiO3基、铋层状结构、(K,Na,Li)NbO3基及钨青铜结构无铅压电陶瓷等体系的研究现状,同时对制备方法也进行了简要的评述,对无铅压电陶瓷的发展趋势作了展望。     

烧结保温时间对KNN-LS-BF-0.15%Cu压电陶瓷性能的影响

采用传统的陶瓷制备工艺,在1 060℃下分别保温2 h、4 h和6 h,制备了{0.996[0.95(Na0.5K0.5)-NbO3-0.05LiSbO3]-0.004FeBiO3}+0.15mol%CuO(简称KNN-LS-BF-0.15%Cu)压电陶瓷,研究了烧结保温时间对陶瓷性能的影响。结果表明,过短的烧结保温时间并不能促成陶瓷晶粒的长成,但超过4 h后继续延长烧结保温时间对晶粒尺寸的影响不大;随着烧结保温时间的延长,KNN-LS-BF-0.15%Cu陶瓷的压电常数d33、机电耦合系数kp和介电常数εr先升高后降低,而介电损耗tanδ和机械品质因数Qm则随之下降;当烧结保温时间为4 h时,样品具有最佳的综合性能:d33=185 pC/N,kp=0.28,εr=1054.25,tanδ=2.1%,Qm=53.39。     

Terfenol-D/PZT/Terfenol-D层状复合磁电传感器磁电效应

采用树脂粘结法制作了L-T型(磁致伸缩层的磁化方向与压电层的极化方向相互垂直)Terfenol-D/PZT/Terfenol-D层状复合磁电传感器。采用等效电路法对磁电系数进行了详细推导,得到磁电系数方程。磁电系数方程显示磁电系数决定于Terfenol-D与PZT的性能参数和磁电传感器中两种材料的体积比。为此从理论和实验上分析了偏置磁场、传感器中两种材料所占的体积比以及驱动磁场频率对磁电系数的影响规律。结果表明偏置磁场、传感器中两种材料所占的体积比和驱动磁场频率对磁电传感器磁电系数的影响都很明显,并且磁电系数的计算结果与实验结果一致,对于所制作的复合磁电传感器,相同条件下磁电系数的计算值与实验值的相对差值小于6%。     

Design and Properties of Piezoelectric Vibrator with Generating Function by FEM Analysis

Bimorph type piezoelectric vibrator with generating function is designed using Finite Element Method (FEM) and fabricated. Design of piezoelectric vibrator by FEM is focused at its length and the weight of added mass. Also, the vibration and charging properties of the fabricated piezoelectric vibrator are investigated. As the FEM analysis results, when the piezoelectric vibrator is the length of 18 mm and the additive weight of 0.3 g, its resonance frequency decrease to 150 Hz. Also, when input voltage of 20 V is applied, output voltage is 10.285 V in generating element. As the properties of piezoelectric vibrator fabricated, when input voltage is 20 V_rms, the acceleration of piezoelectric vibrator and output voltage are about 1.1 G and 10.18 V_rms, respectively. When gold capacitor of 0.0066 [F] is used as the load, the output voltage is about 3 [VDC] after 3600 [sec] driving time.     

Development and Electromechanical Properties of Multimaterial Piezoelectric and Electrostrictive PMN-PT Monomorph Actuators

Monolithic multimaterial monomorphs, comprised of varying ratios of piezoelectric 0.65Pb(Mg_1/3 Nb_2/3)O₃-0.35PbTiO₃ to electrostrictive 0.90Pb(Mg_1/3Nb_2/3)O₃-0.10PbTiO₃, have been co-fired at 1150^∘C. The relative permittivity, displacement, and polarization hysteresis were investigated for varying ratios of piezoelectric to electrostrictive material. The permittivity of the 1:1 multimaterial monomorphs followed the dielectric mixing laws, showing a dielectric constant of 5,500 at room temperature. The P-E hysteresis loop of the 1:1 sample exhibited a maximum and remnant polarization slightly less than the piezoelectric PMN-PT 65/35, but higher than the electrostrictive PMN-PT 90/10. Displacement was found to be higher for the 3:1 monolithic monomorph actuators, reaching 76 μ m at 6 kV/cm. The results indicate that by minimizing the electrostrictive layer thickness the tip displacement can be substantially increased while maintaining a lower hysteresis than that of the purely piezoelectric counterpart.