Strength Evaluation of Piezoelectric Ceramics under Transient Thermal Environments

The strength of piezoelectric ceramics is analyzed for a plate suddenly exposed to an environmental medium of different temperatures. The admissible temperature jump the material can sustain is studied using the stress- and fracture-toughness-based failure criteria. The critical parameters governing the level of the transient thermal stress in piezoelectric ceramics are identified. Solutions are obtained for the maximum thermal shock that the plate can sustain without failure, under the conditions that (i) maximum local tensile stress equals the tensile strength of the ceramic, and (ii) maximum stress intensity factor for representative pre-existing cracks equals the fracture toughness of the ceramic.     

Fabrication and Evaluation of Porous Piezoelectric Ceramics and Porosity–Graded Piezoelectric Actuators

Porous ceramics of lead zirconate titanate (PZT) were prepared by sintering powder compacts consisting of PZT and stearic acid powders in an air atmosphere; stearic acid was added as a pore-forming agent (PFA). The dielectric, elastic and piezoelectric properties of uniformly porous PZT ceramics were investigated as a function of the porosity volume fraction. Furthermore, a beam-shaped PZT actuator sample with a graded porosity content across its thickness was fabricated by sintering PFA-graded powder compacts. The electric-field-induced bending displacement characteristics of the actuator samples were measured by using strain gauges and were found to be in good agreement with the theoretical predication based on a classical lamination theory.     

基于压电陶瓷优化工艺的设计

压电陶瓷是将机械能与电能进行转化的关键材料,已经应用到了军事、医学、电子信息、汽车工业等多个领域,但是含铅陶瓷有危害性。。通过实验,结果发现铅含量对压电性能影响可以实现优化。这一研究对于国家环保材料的发展有一定的参考价值。     

Fabrication of Piezoelectric Ceramic/Polymer Composite Transducers Using Fused Deposition of Ceramics

The fused deposition of ceramics (FDC) technique was used to fabricate piezoelectric ceramic skeletons for the development of piezoelectric composite transducers with 2–2 connectivity for medical imaging. The green parts were designed to have 30 vol% lead zirconate titanate ceramic (PZT-5H) in the final composites. Physical characterization of the sintered samples revealed that 96% of the theoretical density was achieved. Optical microscopy showed that defects due to the FDC mode of deposition, such as small roads and bubbles, were eliminated, because of improvements in powder processing. The electromechanical properties of the final composites were similar to the properties that were obtained for conventionally made composites. A matching layer and a backing layer, as well as wires and an inductor, were added to each FDC composite to fabricate a functional medical imaging transducer. The devices were tested in water using a steel target 3.5 cm thick. Echoes from the target could be detected with all the transducers that were fabricated using FDC. The sensitivities of the transducers were similar to that of a commercial transducer. However, the ringing was much longer than that for a commercial transducer, because the backing layer was not optimized in the transducers that were fabricated using FDC.     

Measurement of High-Temperature Elastic Properties of Ceramics Using a Laser Ultrasonic Method

Young's modulus and Poisson's ratio of SiC ceramics at temperatures >1400°C were obtained using a laser ultrasonics method that included a Fabry-Pérot interferometer (LUFP). At temperatures <1000°C, Young's modulus and Poisson's ratio measured using the LUFP method agreed well with those measured using standard contact methods, such as the resonance method and the ultrasonic pulse method. These results showed that the LUFP method is a powerful tool for measuring high-temperature elastic properties of advanced ceramics in a noncontact manner.     

Intrinsic Elastic, Dielectric, and Piezoelectric Losses in Lead Zirconate Titanate Ceramics Determined by an Immittance-Fitting Method

The material coefficients of "soft" and "hard" lead zirconate titanate (PZT) ceramics were determined as complex values by the nonlinear least-squares-fitting of immittance data measured for length-extensional bar resonators. The piezoelectric d -constant should be a complex value to obtain a best fitting between observed and calculated results. Because the elastic, dielectric, and piezoelectric losses determined in this process were not "intrinsic" losses, a calculation process to evaluate the "intrinsic" losses was proposed. It was confirmed that the intrinsic losses were smaller than the corresponding extrinsic losses. The intrinsic piezoelectric loss existed in both soft and hard PZTs; ∼50% of the loss of piezoelectric d -constant was derived from the elastic and dielectric losses. The most notable difference between the soft and hard PZTs was observed in their elastic losses.     

Effects of Octahedral Tilting on the Piezoelectric Properties of Strontium/Barium/Niobium-Doped Soft Lead Zirconate Titanate Ceramics

(Pb_1−x−ySr_xBa_y)(Zr_0.976−zTi_zNb_0.024)O₃ solid solutions have been investigated to understand the relationship between structural changes caused by isovalent strontium and barium substitution on the A-site and dielectric and piezoelectric properties. As strontium and barium were substituted for lead, the zirconium:titanium (Zr:Ti) ratio was modified so that all compositions had an optimized piezoelectric coefficient (d₃₃). The value of d₃₃ was at a maximum in the tetragonal phase near, but not at, the morphotropic-phase boundary (MPB). The real MPB was taken as the Zr:Ti ratio at which X-ray diffraction patterns appeared either pseudocubic or a mixture of rhombohedral and tetragonal. As strontium content increased, optimized d₃₃ also increased from 410 pC/N (x= 0) to 640 pC/N (x= 0.12), commensurate with a decrease in the paraelectric-to-ferroelectric phase transition temperature (T_C) from 350°C (x= 0) to 175°C (x= 0.12). However, for ceramics where x > 0.12, optimized d₃₃ decreased even though the phase-transition temperature was ∼150°C. Low strontium concentration ceramics (x= 0–0.08) contained 80 nm ferrroelectric domains typical of PZT, but high strontium concentration ceramics (x= 0.12–0.16) contained fine-scale domains (20 nm) in some regions of the microstructure. In addition, [110] pseudocubic electron diffraction patterns revealed superlattice reflections at 1/2{hkl} positions associated with rotations of the octahedra in antiphase. Co-doping ceramics with strontium (x= 0.06) and barium (y= 0.06) resulted in the disappearance of the 1/2{hkl} reflections. Optimized d₃₃ (∼520 pC/N, T_C∼ 205°C) for this composition was similar to that of ceramics where x= 0.08, y= 0, which had a T_C of ∼250°C.     

Dielectric, Piezoelectric, and Pyroelectric Properties of Lead Zirconate—Lead Zinc Niobate Ceramics

New piezoelectric and pyroelectric ceramics consisting of antiferroelectric lead zirconate (PZ) and relaxor ferroelectric lead zinc niobate (PZN) are studied from an application view-point of the field-induced antiferroelectric-to-ferroelectric phase transition. An antiferroelectric-ferroelectric phase boundary exists in PbZr_x(Zn_1/3Nb_2/3)_1−xO₃ (PZZN-1000x) close to x = 0.93 to 0.94 at room temperature. A new ferroelectric rhombohedral phase change, F_α–F'_α, at low temperature is found and studied by the temperature dependence of the pyroelectric coefficient. Electrical poling in these ceramics is easy, and the coercive field E_c∼8 to kV/cm is rather low. Samples with compositions in the range PZZN-86 to PZZN-92 have a large electromechanical coupling constant, k (k_t and k₁₅∼50% to 60%), and a low dielectric constant, ɛ_s (ɛ^T₃₃/ɛ₀= 260 to 320, ɛ^T₁₁/ɛ₀= 380). PZZN ceramics appear to be potential candidates for high-frequency ultrasonic transducers used in the thickness shear mode. The pyroelectric figure of merit (F_v) of these ceramics is comparable to the values published for the PZT-based or PbTiO₃-based materials.     

Elastic Properties of Model Porous Ceramics

The finite-element method (FEM) is used to study the influence of porosity and pore shape on the elastic properties of model porous ceramics. Young's modulus of each model is practically independent of the solid Poisson's ratio. At a sufficiently high porosity, Poisson's ratio of the porous models converges to a fixed value independent of the solid Poisson's ratio. Young's modulus of the models is in good agreement with experimental data. We provide simple formulas that can be used to predict the elastic properties of ceramics and allow the accurate interpretation of empirical property–porosity relations in terms of pore shape and structure.     

Mn掺杂对铌钽酸盐无铅压电陶瓷性能的影响

采用传统固相反应法制备了Mn掺杂的(K,Na,Li)(Nb,Ta)O3无铅压电陶瓷,研究其介电和压电性能.实验结果表明,MnCO3的加入使样品的烧结温度降低,提高了陶瓷的致密性和压电性能.当MnCO3的添加质量分数为0.2 %的时候,样品的性能达到最佳.     

压电陶瓷PZN-PZT对压电复合材料性能的影响

本研究采用固相烧结法合成了PZN-PZT压电陶瓷粉体,并用XRD分析了其晶相组成。将PZN-PZT陶瓷粉体与PVDF复合,制备出PZN-PZT/PVDF0-3型压电复合材料,研究了陶瓷质量分数对复合材料铁电性、介电性及压电性的影响。结果表明,复合材料的铁电性、介电性和压电性能随陶瓷含量的增加而增强,当陶瓷含量为90%时,复合材料的剩余极化强度Pr达到5.27μC·cm-2,矫顽场EC为76kV·cm-1,介电常数εr为188,介电损耗tanδ为0.065,压电常数d33则达到33.4pC/N。     

BNT基无铅压电陶瓷材料的溶胶-凝胶法制备及电性能研究

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。本文采用溶胶-凝胶法制备了BNT(钛酸铋钠)粉体,采用干压成型、高温电炉烧成无铅压电陶瓷样品,并对BNT粉体及无铅压电陶瓷样品进行了性能分析与结果讨论。     

提高点火用压电陶瓷元件性能的研究

本文从理论上对压电点火器的点燃率及使用寿命与压电材料性能的关系进行了讨论,并据此开发出点燃率和放电灵敏度高,使用寿命长达60万次的点火用压电陶瓷材料。     

Influence of Compaction and Granulation Processes on the Properties of Soft Magnetic Ceramics

The granulation and compaction processes are investigated in relation to the influence they have on the magnetic permeability and electromagnetic power losses of conventionally prepared polycrystalline manganese-zinc ferrites. It appears that, during granulation by spray-drying, rapid evaporation conditions may be reached at the internal of the under drying droplets, giving rise to the formation of large void defects in the interior of the granulate. Those defects may resist compaction and also be present in the compacted specimens, eventually leading to large intragranular isolated pores and lower densities at the sintered material; the magnetic properties of the material are therefore negatively influenced. Compaction at high pressures (e.g., >500 kg cm⁻²) may compensate for the existence of inflation defects by causing their removal on compaction. The previous phenomenon is absent in granulates made by the roll granulation process that exhibit, in general, a better compaction, sintering, and magnetic behavior when compared to spray-drying granulates at conditions where void formation takes place.     

Processing and Properties of Strontium Bismuth Vanadate Niobate Ferroelectric Ceramics

The processing conditions, microstructure, and dielectric properties of strontium bismuth niobate vanadate ceramics, SrBi₂(V _x Nb_{1− x} )₂O₉ (SBVN, with 0 ≤ x ≤ 0.3), were systematically studied. A relative density of >90% was obtained for all the samples using a two-step sintering process. XRD showed that a single phase with the layered perovskite structure of SrBi₂Nb₂O₉ (SBN) was formed with a vanadium content of up to 30 at.%. SEM revealed that the average grain size decreased gradually with an increase in vanadium content. The Curie point was found to gradually increase from ∼418°C for SBN to ∼459°C for SBVN with 30 at.% vanadium. Dielectric constants at room temperature and their respective Curie points were found to peak at a composition with 10–15 at.%; vanadium. Moreover, a high concentration of vanadium (>5 at.%) resulted in a significant increase in tangent loss at low frequencies (<1000 Hz). The relationships between chemical composition, processing condition, microstructure, and dielectric properties of SBVN ferroelectric ceramics are discussed.     

Diffusion of 110mAg Tracer in Polycrystalline and Single-Crystal Lead-Containing Piezoelectric Ceramics

We have conducted diffusion measurements of radioactive ^110mAg tracer in single-crystal PbMgNbO₃–PbTiO₃ (PMN-PT) and in polycrystalline 50Pb(Ni_1/3Nb_2/3)O₃·35PbTiO₃·15PbZrO₃ (PNN-PT-PZ) piezoelectric ceramics. Both materials measured belong to the perovskite family. Diffusion in PMN-PT is characterized by an activation energy of 277 kJ/mol and pre-exponential factor of 0.0034 m²/s and compares well with cation diffusion in high-temperature superconducting YBa₂Cu₃O_7–δ. Diffusion in polycrystalline PNN-PT-PZ, on the other hand, is many orders of magnitude faster and is attributed to grain boundaries. PNN-PT-PZ has a lower activation energy, 168 kJ/mol, and a combined pre-exponential factor ( s δ( D _b)_o, where s is the segregation factor of silver, δ the thickness, and ( D _b)_o the pre-exponential factor for grain boundaries) of 3.7 × 10⁻⁹ m³/s. The unusually large combined pre-exponential factor infers large segregation of silver at the grain boundaries and small solid solubility within the grains. It is possible, using a semiempirical model, to compute metal– (silver–) ceramic interface energies as a function of temperature, from which values of 90 kJ/mol and 0.9 R are obtained for enthalpy and entropy, respectively, for grain-boundary segregation.     

Dielectric and Electromechanical Properties of Chemically Modified PMN-PT-BT Ceramics

A particulate coating process incorporating small amounts of several additives such as titanium, zinc, barium, strontium and iron was used to modify the composition and resultant dielectric and electromechanical properties of a commercially available 0.96(0.91Pb(Mg_1/3Nb_2/3)O₃·0.09PbTiO₃)·0.04BaTiO₃. This method led to intimate mixing of the additives at the nanoscale without an additional ball-mixing process. Low- and high-field characteristics including dielectric properties, induced strain and polarization, and associated hystereses were evaluated for the samples sintered at 1200°C for 4 h. All properties were found to depend on the chemical additives and temperature. Specifically, the addition of small quantities of titanium and barium tended to increase strain and Q _eff while maintaining a low dielectric constant which is a promising result for room temperature transducer applications. The addition of titanium with zinc or iron raised dielectric constant, strain, and polarization with significant increases in the temperature of maximum permittivity. On the other hand, the electromechanical properties of the samples containing barium or zinc with titanium did not exhibit a transition to piezoelectric behavior at the temperature expected from the dielectric measurements.     

BNBMT无铅压电陶瓷的制备及性能研究

本文采用新型溶胶-凝胶制粉技术和传统陶瓷生产工艺制备了0.93Bi0.5Na0.5TiO3-0.07Ba1-xMgxTiO3（简称BNBMT100x）体系无铅压电陶瓷,并对BNBMT陶瓷的晶相特征及其介电和压电性能进行了讨论。XRD分析表明,陶瓷样品均形成了单一的钙钛矿结构固溶体;Mg的加入对陶瓷的介电、压电性能有显著影响;陶瓷的铁电-顺电相变峰显著降低、展宽;介电损耗在室温至200℃范围内较平缓。当x=0.04时,机电耦合系数kp和kt最大,分别为16%和19%,压电常数d33值为111pC/N。     

Improvement in Time-Dependent Displacement Degradation of Piezoelectric Ceramics by Manganese/Indium Addition

High-durability lead zirconate titanate (PZT) ceramics were developed in the present study to prevent time-dependent deterioration of displacement, as well as failure under operation. Current leakage in PZT was decreased by adding elemental manganese, changing the zirconium content from 54.0 to 54.2 mol%, and decreasing the antimony content. Displacement was improved by adding both manganese and indium to the PZT. The present investigation resulted in the development of PZT compositions with high displacement and low time-dependent displacement degradation. These results were confirmed by analyzing stack actuators made from enhanced PZT compositions.     

(1-x)BaTiO3-xKNbO3陶瓷的制备及性能研究

采用复合溶胶凝胶法制粉技术结合传统陶瓷制备工艺,制备了(1-x)BaTiO_3-xKNbO_3陶瓷,对其晶相特征、介电及压电铁电性能进行了研究。在1250℃下烧结的陶瓷形成了单一相的钙钛矿结构固熔体。介电常数随着KNbO_3含量的增加先减小后增加,KNbO_3的加入降低了陶瓷的介电损耗。样品的居里温度也在120℃之间波动。KNbO_3的加入使样品的压电常数d_33值逐渐减小。样品BT的d_33值最大,为140pC/N。样品的剩余极化强度(Pr)随着KNbO_3含量的增加而减小,由7μC/cm~2降为3μC/cm~2;矫顽场强(EC)随KNbO_3含量的增加呈现出变小的趋势,样品BT-KN10的矫顽场强(E_C)为4kV/cm。