Lead-free piezoelectric ceramics vs. PZT?

Investigations in the development of lead-free piezoelectric ceramics have recently claimed properties comparable to that of PZT-based materials. In this work, the dielectric and piezoelectric properties of the various systems were contrasted in relation to their respective Curie temperatures. Analogous to PZT, enhanced properties are noted for morphotropic phase boundary (MPB) compositions in the Na,BiTiO₃–BaTiO₃ and the ternary system with K,BiTiO₃, but offer properties significantly lower than that of PZTs. The consequence of a ferroelectric to antiferroelectric transition well below T _C further limits their usefulness. Though comparable with respect to T _C, enhanced properties reported in the K,NaNbO₃ family are the result of increased polarizability associated with the T _{orthor-tetragonal} polymorphic phase transition being compositionally shifted downward and not from a MPB as widely reported. As expected, the properties are strongly temperature dependent unlike that observed for MPB systems.     

Resonant frequency temperature coefficients for the piezoelectric resonators working in various vibration modes

Resonant frequency temperature coefficient is dependent on material properties, resonator dimensions and vibration mode. It could be effectively tuned by the resonator dimensions or by the domain structure in ferroelectric crystals. Optimum dimensions for the zero temperature coefficient resonator are calculated for ring radial vibration mode as a function of resonator dimensions (r ₂/r ₁ = 3.8 for hard PZT ceramics, APC841 type). There are similar results of the temperature coefficient calculations for PZT ceramics and crystal resonators. The temperature coefficient is generally smaller for higher overtones of resonant mode.     

一种新型的压电陶瓷驱动电源研究

为了满足压电陶瓷对驱动电源纹波小的要求,基于两路交错并联电源电路的研究,提出了四路交错并联boost 驱动电源电路的拓扑.四路交错并联boost驱动电源电路中的四条支路可减小输入电流纹波,同时还可减小输出电压纹波,可满足压电陶瓷对驱动电源高稳定性、低纹波、高效率的要求.分析了四路交错并联boost电源电路的基本原理,通...     

Lead-free piezoelectric ceramics based on perovskite structures

The piezoelectric properties of a solid solution based on three components of bismuth sodium titanate (Bi_1/2Na_1/2)TiO₃ (BNT), bismuth potassium titanate, (Bi_1/2K_1/2)TiO₃ (BKT), and barium titanate, BaTiO₃ (BT), that is x(Bi_1/2Na_1/2)TiO₃−y(Bi_1/2K_1/2)TiO₃−zBaTiO₃, [, abbreviated as BNBKy:z(x)] and potassium niobate, KNbO₃ (KN) based ceramics, that is KN+MnCO₃ x wt.%, [abbreviated as KN−Mn x], were studied as a lead-free piezoelectric material. In the case of BNBK2:1 system, high piezoelectric properties were obtained near the MPB composition, and the highest electromechanical coupling factor, k ₃₃ and piezoelectric constant, d ₃₃, were 0.58 for BNBK2:1(0.89) and 181 pC/N for BNBK2:1(0.88). Nevertheless, the depolarization temperature, T _d , shifts to lower temperature around the MPB compositions, and the T _d ’s of BNBK2:1(0.88–0.90) are only about 100 °C. On the tetragonal side, the T _d shifts to higher temperature with increasing the lattice anisotropy, c/a. As T _d higher than 200 °C was obtained in the range of x < 0.78, with a k ₃₃ and d ₃₃ for BNBK2:1(0.78) being 0.45 and 128 pC/N, respectively. In the case of Mn doped KN ceramics, dense and non deliquescence KN ceramic were successfully obtained via ordinary firing technique in air by optimizing the fabrication process. Mn doping for KN ceramics was effective to obtain full poling state easily under poling conditions of high temperature and high electric field. As a result, we obtained the excellent piezoelectric properties of k ₃₃ = 0.507 for KN−Mn0.2.     

Basic investigations on a piezoelectric bending actuator for micro-electro-mechanical applications

Abstract

This article deals with basic investigations into the development and manufacturing process of a piezoelectric animated micro actuator. The concept of the fabrication of a piezoelectric microactuator will be introduced and first fundamental investigations on materials characterization and process technology for the Pt bottom electrode and piezoelectric PZT layer will be presented. PZT thin film have been deposited with the chemical solution deposition (CSD) technique and have been characterized with dielectric and ferroelectric measurements. For optimization of actuator properties an analytical approach and a simulation with finite element method was carried out. This shows that the cantilever must have a length above 300 μm to reach a tip deflection higher than 10 μm at voltages comparable to those used in integrated circuits (IC). Additionally, stress measurements of each layer have been used to characterize the films mechanically.     

Dielectric and piezoelectric properties of La2O3 doped (Bi0.5Na0.5)0.92(Ba0.8Sr0.2)0.08 TiO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics (Bi_0.5Na_0.5)_0.92(Ba_0.8Sr_0.2)_0.08 TiO₃+x mol% La₂O₃(x = 0, 0.1, 0.3, 0.5, 0.8) were synthesized by conventional solid state reaction. The crystal structure of all compositions is mono-perovskite ascertained by XRD. The grain size decreased and diffuse phase transition behavior was more evident with the increasing amount of La₂O₃. The piezoelectric constant d₃₃ and the electromechanical coupling factor k_p showed the maximum value of 165 pC/N and 0.322 at 0.3% and 0.1% La₂O₃ addition, respectively, and rapidly decreased when La₂O₃ addition over 0.5%. The loss tangent tanδ linearly increased and the mechanical quality factor Q_m linearly decreased with the increasing amount of La₂O₃.     

The inferences of ZnO additions for LKNNT lead-free piezoelectric ceramics

By the conventional solid-state liquid-phase sintering technique, Li_0.058(K_0.480Na_0.535)_0.966(Nb_0.9Ta_0.1)O₃ + x wt% ZnO (x = 0, 0.2, 0.4, 0.6, 0.8, 1, 3) lead-free piezoelectric ceramics were fabricated. The addition of ZnO liquid-phase sintering promoters could improve the grain-growth of LKNNT ceramics significantly and its inferences were investigated detailed in this paper. The crystal phases and micro-structures were analyzed by means of the X-ray diffraction and scanning electronic microscopy, respectively. Using the impedance analyzer, the dielectric constant, loss tangent, Curie temperature, phase transition point, and electromechanical coupling factor were measured. And the piezoelectric constants were measured by the d₃₃ meter. Compared to pure LKNNT ceramic (sintered at 1090°C, d₃₃ = 279 pC/N, and k_p = 0.46), for x = 0.6 specimen, even though the optimal d₃₃ and k_p values were only 272 pC/N and k_p = 0.44, but the optimal sintering temperature have been improved from 1090°C to 1020°C successfully.     

Low-temperature sintering of MnO2-doped PZT–PZN Piezoelectric ceramics

The effect of MnO₂ addition on the microstructural evolution and piezoelectric properties of low temperature sinterable PZT–PZN ceramics was investigated. When a small amount of MnO₂ (≤0.5 wt% ) was added, the Mn ions were homogeneously dissolved in the PZT–PZN ceramics, leading to full densification at a temperature as low as 930 °C. However, the further addition of MnO₂ hindered the densification, causing the specimen to have a high porosity and small grain size. In addition, as the MnO₂ content increased, the crystal structure of the PZT–PZN changed gradually from a tetragonal to a rhombohedral phase, due to the substitution of Mn for the B-sites in the perovskite structure. The addition of MnO₂ up to a maximum of 0.5% improved the mechanical quality factor (Q _m) of the PZT–PZN ceramics markedly, while keeping the k _p and d ₃₃ values reasonably high. The 80% PZT–20% PZN doped with 0.4 wt% MnO₂ exhibited excellent piezoelectric properties; Q _m = 1,000, k _p = 0.62, and d ₃₃ = 330 pC/N.     

High amplitude vibration of piezoelectric bending actuators

The properties of several configurations of piezoelectric bending actuators were investigated at high vibration amplitude both theoretically and experimentally. It was found that under high amplitude vibration conditions, the failure of the actuator was mainly caused by the maximum stress and domain reorientation. The actuator tends to fracture or crack at the location of maximum stress, which is indicated by the sudden drop of the displacement during frequency scan. The dimension, boundary condition and vibration order influence the distribution and magnitude of the stress. Domain reorientation may also occur during the frequency scan, which results in the distortion of the current profile. And meanwhile the magnitude of the current, admittance and temperature of the actuator will increase significantly and abruptly. The temperature was found to be increase with the increase of frequency, electric field or vibration amplitude due to the higher mechanical and electrical losses. The un-even stress distribution has also resulted in a high-to-low gradient temperature rise from the clamped end to the free end of the actuator under the Clamped-Free boundary condition. A linear model based on Euler–Benoulli theory has been derived and it provides reasonable explanations on the phenomena observed experimentally in this paper.     

Effects of complex doping on microstructural and electrical properties of PZT ceramics

The influence of complex dopants including donor and acceptor ions on microstructure and electrical properties of PZT (Zr/Ti = 53/47) ceramics was investigated. The prepared PZT ceramics modified with complex soft dopants, La⁺³ and Nb⁺⁵, showed that the piezoelectric properties were enhanced and stable with the compositional variations, which made it possible to establish the higher reliability and reproducibility of the piezoelectric performances. For 1.0 mol% La and 1.2 mol% Nb doped composition, the maximum value, k _P = 0.66, was obtained. Unlike single element doping, the complex doping of both the donor and acceptor ions caused various compensation effects for the piezoelectric properties of the PZT ceramics. The improved piezoelectric properties, i.e., enhanced Q _m with remaining higher k _p , were obtained in the PZT composition complexly doped with La⁺³ and Fe⁺³. For 1.0 mol% La and 2.0 mol% Fe doped PZT composition, relatively high Q _m and k _p values of 580 and 0.53, respectively, were obtained. It was also shown that the PZT composition had the rather lowered dielectric constant, ε _r = 800, and considerably low loss, tanδ = 0.003. By changing the dopants compositions, the properties can also be tailored over wider range.     

Influence of sintering temperatures on the electrical property of bismuth sodium titanate based piezoelectric ceramics

A systematic investigation of cerium and stannum doped 0.94(Bi_0.5Na_0.5)TiO₃−0.06BaTiO₃ (Sn&Ce-BNT6BT) based lead-free piezoelectric ceramics is undertaken to understand the influence of sintering temperature on electrical properties. The X-ray diffraction patterns showed that all of the Sn&Ce-BNT6BT ceramics exhibited a single perovskite structure with the co-existence of the rhombohedral and tetragonal phase. The smaller grain size of Sn&Ce-BNT6BT ceramics was obtained at lower sintering temperature, and more cubical grains of Sn&Ce-BNT6BT ceramics were obtained at higher sintering temperature. The temperature dependence of dielectric permittivity of the compositions exhibited strong dispersion with the increasing temperature, and the dielectric loss tangent increased dramatically while the temperature over 225^∘C. The depolarization temperature T _d of Sn&Ce-BNT6BT ceramics sintered at 1160^∘C was 92.6^∘C. The remnant polarizations P _r for Sn&Ce-BNT6BT ceramics sintered at 1120 and 1200^∘C were found to be 28.8 and 33.4 μC/cm² at room temperature, respectively.     

烧结温度对氧化铝陶瓷介质陷阱分布的影响

论文采用等温衰减电流法研究了在不同烧结温度下制备的陶瓷试样的陷阱分布，试验结果表明，烧结温度能够影响到氧化铝陶瓷介质的陷阱分布，微观结构分析表明，不同的烧结温度会导致陶瓷介质不同数量的结构缺陷，从而造成了它们陷阱分布的不同。     

Influence of electric field on the ultrasound velocity in PZT ceramics

The paper deals with the influence of the electric bias field on the ultrasound velocity of various samples of Pb(Zr _x Ti_1−x )O₃ (PZT) ceramics. The ultrasonic velocities were measured on commercial types of PZT ceramics as APC 841, APC 850, and APC 856, at room temperature. The comparison of the ultrasound velocities dependence on electric bias field was made for poled/unpoled soft ceramics. The ultrasonic pulse-echo technique was used in our experiment. The ultrasonic system is based on Matec Instruments, Inc. modules. The time domain response was recorded and time of flight between echoes was directly measured by digital oscilloscope, type Agilent 54622D. The high bias field was applied on disk samples by the high voltage amplifier type Trek 610D, using a special setup and sample holder. The sound velocity was found to change drastically near the coercive field for a PZT ceramics, where the velocity of longitudinal waves decreases with an increasing field while the velocity of shear waves increases, which is caused by the change of the elastic anisotropy under influence of the depolarization field. The consequent change of the piezoelectric contribution to effective elastic constant decreases the velocity of longitudinal waves and at the same time increases the velocity of shear waves around the coercive field.     

Investigation on the design and synthesis of new systems of BNT-based lead-free piezoelectric ceramics

Three primary differences between BNT- and PZT-based ceramics were analyzed from the composition and the active component of the materials. Based on the analysis the authors’ group developed the new idea of the design of the multiple complex in the A-site ions of BNT compounds. (Bi_0.5Na_0.5)²⁺, Bi³⁺ and Na⁺ in the ABO₃ structure are defined as A-site, A₁-site and A₂-site ions, respectively, and A, A₁ and A₂-site ions can be simultaneously or singly substituted partially by alkaline-earth metal ions, metal ions with +3 valence and metal ions with +1 valence, respectively. Under this consideration, Several new systems of Bi_0.5Na_0.5TiO₃ (abbreviated as BNT)-based lead-free piezoelectric ceramics were proposed. These ceramics can be prepared by conventional ceramic techniques and have excellent piezoelectric performance. Among these materials, Bi_0.5(Na_1−x−y K _x Li _y )_0.5TiO₃ possesses higher piezoelectric constant (d ₃₃ = 230 pC/N), higher electromechanical couple factor (k _p = 0.40), larger remanent polarization (P _r = 38.9 μC/cm²) and a better P-E hysteresis loop until about 200^∘C. This work was supported by the projects of NSFC (50410179), (50572066), and (59972020), and NAMMC (2001-AA325060).     

Fabrication and evaluation of PZT/Ag composites and functionally graded piezoelectric actuators

Metallic Ag as the second phase was added into PZT ceramic matrix to fabricate piezoelectric composites and functionally graded actuators by gradually altering Ag concentration, aimed to improve mechanical properties and to solve possible interfacial debonding usually observed in conventional bimorph-type piezoelectric actuator. The PZT/Ag composites were obtained by directly co-firing PZT and Ag powders at 1200^∘C for 1 h. The fracture strength σ _f and fracture toughness K _IC , as well as the corresponding piezoelectric properties, were firstly evaluated upon the PZT/Ag composites for Ag concentrations of 0–30 vol%. The mechanical properties for the PZT/Ag composites were found to be greatly enhanced compared with pure PZT ceramics: from 69 to 129 MPa for σ _f and from 1.0 to 3.7 MPa.m^1/2 for K _IC . With increasing Ag concentration, the piezoelectric constant d ₃₃ of PZT/Ag composites was found to decrease from 419 to 86 pC/N. Then, a functionally graded actuator was fabricated and evaluated in terms of electric-induced curvature k. The PZT/Ag FGM actuator with size of 12 mm × 3 mm × 1 mm has a curvature k of 0.03–0.17 m⁻¹ that corresponds to applied voltages of 100–500 V. A comprehensive comparison was made on the mechanical property enhancements by the metal particles dispersion, and the bending displacements produced by the FGM actuators between the PZT/Ag and previously fabricated PZT/Pt systems.     

Effects of Al2O3 on the piezoelectric properties of Pb(Mn1/3Nb2/3)O3-PbZrO3-PbTiO3 ceramics

Piezoelectric properties of Al₂O₃-doped Pb(Mn_1/3Nb_2/3)O₃-PbZrO₃-PbTiO₃ ceramics were investigated. The constituent phases, microstructure, electromechanical coupling factor, dielectric constant, piezoelectric charge and voltage constants were analyzed. Diffraction peaks for (002) and (200) planes were identified by X-ray diffractometer for all the specimens doped with Al₂O₃. The highest sintered density of 7.8 g/cm³ was obtained for 0.2 wt% Al₂O₃-doped specimen. Grain size increased by doping Al₂O₃ up to 0.3 wt%, and it decreased by more doping. Electromechanical coupling factor, dielectric constant, piezoelectric charge and voltage constants increased by doping Al₂O₃ up to 0.2 wt%, and it decreased by more doping. This might result from the formation of oxygen vacancies due to defects in O^{2 −} ion sites and the substitution of Al³⁺ ions.     

Sintering and dielectric properties of Al2O3 ceramics doped by TiO2 and CuO

The effects of CuO and TiO₂ additives on the microstructure and microwave dielectric properties of Al₂O₃ ceramics were investigated. Al₂O₃ ceramics with CuO and TiO₂ additions can be well sintered to achieve 93∼98% theoretical densities below 1,360 °C due to Ti₄Cu₂O liquid phase sintering effect. The Qf values decreased with increasing CuO and TiO₂ content, due to the formation of the second phase Ti₄Cu₂O. However, the varying behaviors of the dielectric constant (ɛ _r ) and temperature coefficients (τ _f ) were associated with phase constitutions, as a result of the change of CuO and TiO₂content. The τ _f can be shifted close to 0 ppm/°C by controlling the content of CuO and TiO₂. The specimens with 0.5 wt.% CuO and 7 wt.% TiO₂ sintered at 1,360 °C for 4 h showed ɛ _r of 11.8, Qf value of 30,000 GHz, and τ _f of −7 ppm/°C.     

Determination of piezoelectric parameters from the measured natural frequencies of a piezoelectric circular plate

Due to the complexity of electro-elastic coupling characteristics in piezoelectric materials, some elastic, dielectric and piezoelectric parameters are difficult to measure. Usually, these parameters are determined by assuming that all other parameters remain constant during the measurement. However, the interactive effect between material properties makes this assumption not always true. In this study, the measured natural frequencies of the specified circular piezoelectric plate are used to extract these parameters simultaneously. In other words, all these parameters are determined with consideration of the interactive electro-elastic coupling effect.

The analytic model of a free-free circular piezoceramic plate was derived and solved to establish the relationship between natural frequencies and their material parameters. In order to cover most of the parameters, the out-of-plane (non-symmetric transverse) and in-plane (symmetric extensional) modes are considered.

The genetic algorithm is employed to determine most of the elastic, dielectric and piezoelectric parameters from a least square error between the calculated and measured natural frequencies. The numerical results derived from the parameters proposed in this work reveal that they coincide well with the measured data. In other words, the proposed method for extracting piezoelectric parameters is both feasible and effective.     

The Effect of Sintering Processes on the Properties of Mn-F Doped PZT Ceramics

Fluoridated PZT ceramics were produced by solid-state and liquid-phase sintering methods, according to the formula Pb(Zr_0.52Ti_0.48)_1-xMn_xO_3-yF_y, where 0 < x < 0.015 and 0 < y < 0.1. The effects of sintering processes on the phase development and microstructure of Mn-F doped PZT ceramics have been investigated using XRD and FEGSEM. In solid-state sintering, the fluoride additive enhanced the densification of PZT ceramics, enabling densification to >95% relative density at a temperature as low as 1000°C. However, fluoride loss at high temperatures was found to be a significant problem. Alternatively, ceramics with a density >92% were prepared by sintering at a temperature of 850°C by incorporating a eutectic mixture of PbO and V₂O₅ as sintering aid. Problems associated with volatilization of fluoride compounds during sintering could be alleviated using this approach. EPMA was employed to analyze the distribution of the additives in the calcined powders and sintered ceramics. The nonlinear dielectric properties were determined by measuring P-E loops, using an AC electric field in the range 0.1 to 2.0 kV mm^?1.     

Effects of ZnO on the piezoelectric properties of Pb(Mn1/3Sb2/3)O3-Pb(Zr,Ti)O3 ceramics

Perovskite-type 0.05 Pb(Mn_1/3Sb_2/3)O₃-0.95 Pb(Zr_0.5Ti_0.5)O₃ (PMS-PZT) was synthesized by conventional bulk ceramic processing technique. ZnO as a dopant up to 0.5 mol% was incorporated into the PMS-PZT system, and the effects on piezoelectric properties were investigated. Pyrochlore phase was not detected to form during the synthesis of the PMS-PZT system with 0∼0.5 mol% ZnO addition. The highest density of 7.92 g/cm³ was obtained when sintered at 1200°C for 2 hrs. Piezoelectric properties as a function of ZnO content were evaluated using a gain phase analyzer. Piezoelectric charge constant (d₃₁) and piezoelectric voltage output coefficient (g₃₁) increased up to −130 pC/N and −24.9 × 10³Vm/N, respectively, with increasing ZnO content. Mechanical quality factor (Q _m) was shown to reduce considerably with increasing ZnO content. When 0.3 mol% of ZnO was added into the system, electromechanical coupling factor (k _p) and relative dielectric constant () reached to the maximum of 56% and 1,727, respectively.