Causes of Instability and Aging of Piezoelectric Power Ceramics

A simple model of substituted perovskites of the PZT type involving the presence of centers which can act both as donors and acceptors provides an explanation of the cancellation of space charge density (ρ=−div     ) in polarized ceramics. A cause of instability can be avoided by incorporating substitutions in the cation lattice to form these centers and lock them in position. These substitutions insure the nonconductive state of the material although they allow a short-range electron transfer between the centers.     

Low-Temperature Sintering of Lead-Based Piezoelectric Ceramics

The low-temperature sintering of lead-based piezoelectric ceramics has been studied. The sintering temperature of lead zirconate titanate (PZT) ceramics could be reduced from ∼ 1250° to ∼960°C by the addition of a small amount of the lower-melting frit, B₂O₃–Bi₂O₃—CdO. It exhibited the following dielectric and piezoelectric properties: K_p= 0.52 to 0.58, Q_m= 1000, ε^T₃₃/ε₀= 800 to 1000, tan δ= 50 × 10⁻⁴, ρ= 7.56 to 7.64 g/cm³. Ceramics with the aid of suitable dopants (CdO, SiO₂, and excess PbO) in the Pb-(Ni_1/3Nb_2/3)O₃—PZT family could be sintered at 860° to 900°C. For these materials, K_p= 0.56 to 0.61, Q_m= 1000, ε^T₃₃/ε₀= 1500 to 2000, tan δ≤ 50 × 10⁻⁴, ρ= 7.80 to 8.03 g/cm³. The microstructure, sintering mechanism, and the effects of various impure additions have been analyzed by means of scanning electron microscopy, scanning transmission electron microscopy, electron probe microanalysis, and X-ray photoelectron spectroscopy.     

Ferroelectric-Domain Structure in Piezoelectric Ceramics

Twin-related (tetragonal (T), rhombohedral (R)) adjacent ferroelectric domains, which require a smaller energy for the rotation of the polarization vector, have been found to occur in lead zirconate titanate type piezoceramics at the morphotropicphase boundary, explaining the triplet splitting observed in electron diffraction patterns. The values of elastically stored energy density in the walls of the twinning domains are estimated, and a packing model of the ferroelectric domain structure as a T₁RT₂RT₁…succession is proposed to explain the coexistence of the two ferroelectric phases in the morphotropicphase boundary region. A crystallographic analysis of the transformation from the paraelectric to the ferroelectric phase is performed on the basis of martensite transformation theory. The calculated results are in good agreement with the observed transmission electron microscopy data. In particular, the crystallography and morphology of the "herringbone" domain structure, often observed in piezoelectrio ceramics, are well explained by this analysis.     

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.     

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.     

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.     

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.     

Poling of Lead Zirconate Titanate Ceramics and Flexible Piezoelectric Composites by the Corona Discharge Technique

In the conventional poling method, piezoelectric ceramics and composites are poled by applying a large dc voltage. Poling of composites having a polymer matrix with 0–3 connectivity is especially difficult because the electric field within the high-dielectricconstant grains is far smaller than in the low-dielectric-constant polymer matrix. Therefore, very large electric fields are required to pole these types of composites. However, large electric fields often cause dielectric breakdown of the samples. In this study for improved poling, the corona discharge technique was used to pole piezoelectric ceramics, fired PZT composites, and 0.5PbTiO₃· 0.5BiFeO₃ 0–3 polymer composites. An experimental setup for corona poling is described. The dielectric and piezoelectric properties of materials poled by the corona discharge technique were comparable to those obtained with the conventional poling method.     

锑掺杂PZSN压电陶瓷烧结工艺的研究

为制备大功率低损耗压电陶瓷材料，对改性锆钛酸铅压电陶瓷Pb0.9Ba0.05Sr0.05（Zn1／3Nb2／3）0.06（Sn1/3Nb2/3）0.05Ti0.44Zr0.44O3＋0．5％Mn（NO3）2（质量分数，下同）＋x％Sb2O3的烧结工艺进行比较研究，结果表明体系优化结工艺为以300℃／h的升温速率，在1250℃处保温3h，此时对0．1％～0．4％（质量分数）的Sb2O3掺杂，均可制备出综合性能优良的压电陶瓷。当掺杂量为0．1％（质量分数）时，其tanδ，Qm，Kp，d33和ε4分别为0．47％，2251，0.538，336pC／N和1897，可满足大功率应用的要求。     

Novel Synthesis Route to Make Nanocrystalline Lead Zirconate Titanate Powder

The present research describes synthesis of perovskite lead zirconate titanate (PZT) nanocrystalline mesoporous powders from the aqueous solutions of Pb²⁺, Zr⁴⁺, and Ti⁴⁺ metal ions using sucrose as a template material. Sucrose retains the metal ions in solution through complex formation. Dehydration and thermal decomposition of the metal ion–sucrose mass produces a large amount of gas, which helps to create porosity and high surface area in the final products. The particle size of the synthesized powder is between 50 and 60 nm, with a average specific surface area between 20 and 25 m²/g. The surface area increases as the amount of sucrose increases. Nanocrystalline PZT powder with high surface area can be useful for low-temperature sintering.     

水基凝胶注模成型PZT压电陶瓷的形变控制

采用凝胶注模成型工艺,在控制温度和湿度条件下制备出锆钛酸铅(PZT)压电陶瓷.研究了凝胶体系化学成分对陶瓷大圆片形变的影响规律,并将其微观结构与干压成型工艺制备的陶瓷进行对比.结果表明,固定单体与交联剂比例,随单体浓度增加,凝胶时间不断减小,素坯变形率先减小后增大,单体浓度为210 g/L时,素坯变形率最小.在此单体浓度下,随单体与交联剂比例增大,凝胶时间不断减小,但素坯变形率变化不规律.固定单体与交联剂比例,引发剂用量较少时,素坯无法成型,而引发剂用量较大则导致素坯更大变形.这些复杂的形变变化均与凝胶网络结构形成的聚合及交联反应有关.在最佳单体浓度、单体与交联剂比例及引发剂用量条件下,通过高温低湿的干燥工艺,制备出直径约为180mm的无翘曲大面积PZT陶瓷.与干压成型工艺制备的PZT陶瓷相比,采用凝胶注模成型工艺制备的PZT陶瓷具有类似的微观结构及电学性能.通过工艺优化可将凝胶注模工艺用于制备无变形大面积压电陶瓷材料,以及特种换能器等声学器件.     

Processing and Properties of Screen-Printed Lead Zirconate Titanate Piezoelectric Thick Films on Electroded Silicon

The printing of lead zirconate titanate (PZT, Pb(Zr,Ti)O₃) piezoelectric thick films on silicon substrates is being studied for potential use as microactuators, microsensors, and microtransducers. A fundamental challenge in the fabrication of useful PZT thick-film devices on silicon is to sinter the PZT to high density at sufficiently low temperature to avoid mechanical or chemical degradation of the silicon substrate. The goal of the present study is to develop and implement suitable electrodes and PZT sintering aids that yield attractive piezoelectric properties for devices while minimizing reactions between the silicon, the bottom electrode, and the PZT thick film. A B₂O₃-Bi₂O₃-CdO sintering aid has been found to be superior to borosilicate glass, and the use of a gold/platinum bilayer bottom electrode has resulted in better thermal stability of the electrode/film structure. Films sintered at 900°C for 1 h have relative permittivity of 970 (at 1 kHz), remnant polarization of 20 μC/cm², coercive field of 30 kV/cm, and weak-field piezoelectric coefficient d ₃₃ of 110 pm/V.     

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.     

Influence of Microstructure on the Dielectric and Piezoelectric Properties of Lead Zirconate-Polymer Composites

Composites with 0–3 connectivity were fabricated from lead zirconate titanate (PZT) and phenolic resin powders. These composites were investigated for dielectric and piezoelectric properties with variations in active particle density and PZT-polymer interface porosity. The dependence of dielectric and piezolectric properties on interface porosity is discussed, especially in terms of porosity factors. The dependence of the piezoelectric constant on interface porosity was greater than that of the dielectric constant. The interface pores play the role of a stress buffer. Thus local stress applied on PZT particles in the composites was remarkably diminished. When particle porosity was high, the dependence of the dielectric and piezoelectric constants on interface porosity decreased.     

Control of Crystal Orientation and Piezoelectric Response of Lead Zirconate Titanate Thin Films Near the Morphotropic Phase Boundary

PbZr_0.53Ti_0.47O₃ (PZT) thin films with various preferred crystallographic orientations were synthesized on various substrates using pulsed laser deposition techniques. Larger piezoelectric displacement, which involved the bending vibration of the PZT film/substrate, was observed in randomly oriented PZT thin film than that in (100)- and (111)-preferred texture films. This result was discussed by correlation with the number of effective spontaneous polarization axes in the morphotropic phase boundary of the PZT system. Moreover, polarization fatigue was found to lower the electric-field-induced displacement significantly, indicating a large contribution of ferroelectric domain motion to the piezoelectric response of PZT thin films under bipolar drive.     

Effect of Ba2+ Substitution on Dielectric and Electric-Field-Induced Strain Properties of PMN–PZ–PT Ceramics

Effect of Ba²⁺ substitution for Pb²⁺ on the dielectric and electric-field-induced strain characteristics of the PMN–PZ–PT ceramics has been investigated in the compositions of the tetragonal-rich 0.2PMN–0.36PZ–0.44PT and rhombohedral-rich 0.2PMN–0.4PZ–0.4PT ceramics. The phase approached cubic structure from the tetragonal and rhombohedral, and grain size was reduced when the Ba²⁺ cation was substituted. As Ba²⁺ content increased, frequency-dependent relaxor-like behavior of the dielectric constant was observed at temperatures below the dielectric maximum ( T _max) for compositions with 20 and 25 mol% Ba²⁺. Electric-field-induced strain was maximized in the 12 mol% Ba²⁺-substituted 0.2PMN–0.4PZ–0.4PT specimen ( S _max= 0.15%), and maximum piezoelectric, d ₃₁, was 300 in the 14 mol% Ba²⁺-substituted 0.2PMN–0.4PZ–0.4PT specimen.     

Properties of Modified Lead Zirconate Titanate Ceramics Prepared at Low Temperature (800°C) by Hot Isostatic Pressing

High-density lead zirconate titanate (PZT) ceramics were fabricated for the first time at a temperature as low as 800°C via the hot isostatic pressing (HIP) of a PZT powder with a modified composition of 0.92Pb(Zr_0.53Ti_0.47)O₃—0.05BiFeO₃—0.03Ba(Cu_0.5W_0.5)O₃ that contained 0.5 mass% MnO₂. The resultant PZT ceramics exhibited a microstructure that was denser and finer than that of PZT sintered at 935°C, which is the lowest temperature for the densification of the same composition via normal sintering. The relevant dielectric and piezoelectric properties of the HIPed PZT ceramics were as follows: coefficient of electromechanical coupling ( K ₃₁), 31.8%; mechanical quality factor ( Q _m), 1364; piezoelectric constant ( d ₃₁), −73.7 × 10⁻¹² C/N; relative dielectric constant (ɛ₃₃^T/ɛ₀), 633; dielectric loss factor (tan δ), 0.5%; Curie temperature ( T _c), 285°C; and density (ρ), 8.06 g/cm³. In addition to these reasonably good piezoelectric properties, the HIPed PZT exhibited better mechanical properties—particularly, higher fracture strength—than the normally sintered PZT.     

倒车雷达用锆钛酸铅压电陶瓷材料的研究

对锆钛酸铅陶瓷材料进行了Nb2O5、SrCO3微量掺杂改性研究,观察了掺杂后陶瓷样品的显微结构,研究了其相对介电常数、压电常数、机电耦合系数及电容量变化率随测试温度变化的规律。实验结果表明:Nb2O5、SrCO3掺杂后,陶瓷结构致密,介电损耗减少,相对介电常数、压电常数、机电耦合系数明显提高,电容量变化率明显改善。当Nb2O5、SrCO3的添加量为0.6wt%时,制得的压电陶瓷材料具有最佳的压电性能:εr=2100,D33=450pC/N,Kp=0.81,ΔC/C10%(-55~85℃),可以满足高性能的汽车倒车雷达的应用要求。     

PMN-PT系统中偏置电场诱导压电效应的研究

通过测定PMN-PT系统中不同PT含量时的介温谱、电滞回线和偏置电场诱导下的压电性能探讨了(1-x)PMN-xPT系统(x=0～0.4))的组成、结构与性能之间的关系.实验结果表明,当x＜0.07时,PMN-PT材料表现为典型的弛豫铁电体;当0.07＜x＜0.13时,材料具有弛豫铁电体为主的过渡型结构;当0.13＜x＜0.33时,具有普通铁电体为主的过渡型结构;当x=0.33～0.34时,材料位于准同型相界,而当x＞0.34,PMN-PT则表现为普通铁电体.     

Calculations and Measurements of the Spatial Piezoelectric Response and of the d15 Parameter of PZT5A Ceramic

In the analytical section of this paper the magnitudes of the polarization vectors ( Pi ) of lead zirconate titanate are shown as they vary with the angle of an applied uniaxial stress. This is done by applying a directional cosine matrix to the stress tensor σ _jk in Pi = d _ijk σ _jk . In addition the polarization in the direction of a rotating stress is derived from rotating the d _ijk tensor. Two-dimensional as well as three-dimensional isometric plots of the results are shown. The experimental section describes the preparation of disks poled uniformly at 90° to their thickness and the use of the Berlincourt d ₃₃ meter to measure d ₃₃₃ as a function of angle. Very good agreement with the calculated results was obtained. The effect of electrodes on the measurement of d ₃₃ and the use of a d ₃₁ parameter to permit a d ₁₅ determination are also demonstrated. The d ₃₃₃ measurements provided a d ₁₅ value with a resolution of ± 8%. Its average value was within 5% of d ₁₅ values derived with other techniques.