High-power properties of piezoelectric hard materials sintered at low temperature for multilayer ceramic actuators

0.05Pb(Mn_1/3Sb_2/3)O₃–0.05Pb(Al_1/2Nb_1/2)O₃–0.9Pb(Zr_0.48Ti_0.52)O₃ (PMS–PAN–PZT) high power piezoelectric system with both La₂O₃ as a hardener and CuO as a low sintering agent had been synthesized at 900 °C for 2 h. When La₂O₃ doping of the main composition went over 0.5 wt%, the mixed tetragonal and rhombohedral perovskite structure changed to pure rhombohedral perovskite structure. In case of the CuO, 1.0 and 1.5 wt% CuO content significantly improved the sinterability of the PMS–PAN–PZT system processed at 900 °C for 2 h. When La₂O₃ and CuO co-doped in PMS–PAN–PZT ceramics, piezoelectric constants (d₃₃), quality factor (Q_m), electromechanical coupling factor (k_p) and dielectric constant (${\epsilon }_3^{\text{T}}/{\epsilon }_0$) of the piezoelectric ceramics sintered at 900 °C for 2 h were optimized, such as 336 pC/N, 841, 60%, and 1358, respectively. New developed piezoelectric materials are promising for high power multilayer ceramic actuators.     

Fracture behavior of poled piezoelectric PZT under mechanical and electrical loads

Four point bending samples were poled parallel to the long axis, notched and fractured. During mechanical loading, a constant electric field was applied parallel or antiparallel to the poling direction (perpendicular to the crack surface). Assuming electrical crack boundary conditions of (i) an impermeable or (ii) a completely permeable crack, the stress intensity factors K_I and the field intensity factors K_IV at failure were determined by linear-piezoelectric finite element calculations. The fracture curve K_IC(K_IV) for the impermeable crack model does not comply to fracture criteria based on the total energy release rate or on the mechanical energy release rate. Within the completely permeable crack model, it appears generally impossible to describe electric field effects on the fracture resistance. Some theoretical extensions of the crack models are discussed which might contribute to resolve the aforementioned problems.     

Phase transition in a shock-loaded piezoelectric ceramic of the PZT system

Combustion, Explosion, and Shock Waves -     

Dielectric and piezoelectric studies of La doped PZT polymer composites

Lanthanum doped Lead Zirconate Titanate (La:Zr:Ti = 4:51:49) has been shaped to porous three dimensional structures through BURPS (Burntout Plastic spheres) process. The materials are then framed to low-density, low-permittivity 3-3 composites with silicone rubber as the second phase. Poled composite ceramics have shown significant increase in piezo-electric voltage coefficients (g₃₃3) with a corresponding drop in dielectric permittivity. Volume fraction of PZT poled is estimated using a theoretical model where the PZT is assumed to be made up of small cubelets of 1 to 2 micrometers in size.     

Influence of PbO stoichiometry on the properties of PZT ceramics and multilayer actuators

Lead-oxide stoichiometry of lead-zirconate-titanate (PZT) ceramics and multilayer actuators is a critical issue for fabrication and performance. During sintering, the high vapor pressure and the corresponding volatility of lead oxide (PbO) require a careful design of sintering setup and parameters, as both may significantly impact on the PbO content in ceramics and devices. In order to investigate the effects of PbO stoichiometry, PZT compositions with different PbO contents have been synthesized and were sintered under varying temperature conditions and sintering setups. Structure and microstructure of the material was characterized using X-ray diffraction and scanning electron microscopy (SEM). Dielectric properties and high field strain behavior were analyzed with respect to their relation to PbO content and grain size. Corresponding experiments with multilayer actuators were carried out, whereby the PbO content was varied by controlling the sintering atmosphere. The results indicate that there is a pronounced correlation between PbO content, structure and high field strain in both, PZT ceramics, and multilayer actuators.     

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

The PZT/Pt composites with various compositions were fabricated by using powder processing, and their mechanical, dielectric, piezoelectric and elastic properties were evaluated with the purpose to develop piezoelectric actuators with functionally graded microstructure (FGM). The piezoelectric and dielectric constants of the PZT/Pt composites decreased monotonously with increasing Pt content, whereas the addition of the Pt particles greatly improved the mechanical properties, particularly the fracture toughness in the composites. Miniature bimorph-type FGM actuators that consist of a composite internal-electrode (70 vol.%PZT/30 vol.%Pt) and three piezoelectric layers (100 vol.%PZT to 80 vol.%PZT/20 vol.%Pt) were fabricated by powder stacking and normal sintering techniques. The electrically-induced deflection characteristics of such an FGM actuator were measured with electric strain gages mounted on the top and bottom surfaces of the actuators, and the measured data were consistent with the analytical results given by the modified classical lamination theory model (CLT).     

Non-linear dielectric and piezoelectric response in undoped and Nb5+ or Fe3+ doped PZT ceramic system

The dielectric and direct piezoelectric responses in doped and undoped Pb(Zr_1−xTi_x)O₃, with x = 0.40, 0.47 and 0.60, are experimentally studied. The permittivity and the direct piezoelectric coefficient have been measured by applying subswitching ac electric field and high ac mechanical stress. The influence of the type of defects and their concentrations on the non-linear response have been explored. The experimental data show a considerable mobility increase of ferroelectric–ferroelastic domain walls in donor-doped samples. The correlation between the dielectric constant and dielectric losses is discussed in terms of the Rayleigh law. Our results reveal that the influence of reversible and irreversible domain wall movements on the non-linear dielectric response is determined by defects associated with dopants. The role played by the crystallographic phase in the non-linear response is also analyzed.     

Fabrication and characterization of low temperature sintered hard piezoelectric ceramics for multilayer piezoelectric energy harvesters

In this study, 0.65Pb(Zr_0.465Ti_0.545)O₃-0.35Pb(Zn_1/6Ni_1/6Nb_2/3)O₃, doped with 3.0 mol% MnCO₃ and 1.0 mol% CuO (M3.0C1.0PZT-PZNN), was investigated as a hard piezoelectric ceramic for multilayer ceramic piezoelectric energy harvesters (MLC-PEHs). These PEHs showed a high output performance that was partly ascribed to the hardening effect of MnCO₃. In contrast, a single-layer ceramic piezoelectric energy harvester (SLC-PEH), containing M3.0C1.0PZT-PZNN, exhibited a higher output power density than that containing an analogous non-Mn-doped soft piezoelectric ceramic (C1.0PZT-PZNN), especially at high accelerations. In the fabricated MLC-PEH, containing an M3.0C1.0PZT-PZNN-based five-layer ceramic and a pure Ag inner electrode, no interdiffusion was observed between the electrode and the ceramic layers, and the corresponding interface was clear and smooth. This MLC-PEH, which exhibited a high output power density and a relatively large current, was used to charge a 0.22 F capacitor at its resonance frequency and an acceleration of 1.5 G, achieving a charging rate higher than that of the SLC-PEH.     

Effects of microwave heating on dielectric and piezoelectric properties of PZT ceramic tapes

Commercial lead zirconate titanate (PZT) perovskite powders were used to fabricate ceramic tape and then sintered by microwave and conventional methods. Both dielectric and piezoelectric properties of PZT ceramic tapes were studied in terms of sintering process. X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM) show the PZT perovskite phase with smaller grain size and dense microstructure can be obtained at a lower sintering temperature by microwave process. It was also observed that shrinkage ratio and bulk density of the tapes sintered at 800 °C were obtained about 19% and 7.46 g/cm³ by the microwave heating method, respectively, that is corresponding to those values of sintered PZT tapes at 950 °C by conventional process. Moreover, the dielectric constant and maximum permittivity are increased about 30% as compared with conventional processing method. The experimental results demonstrated that the characteristics of the PZT tapes could be significantly improved by microwave heating method. These results demonstrate that such a simple approach can upswing the piezoelectric and dielectric properties of these tapes by using microwave process with a short heating time.     

Piezoelectric and dielectric characteristics of lead-free BNKLBT ceramic thick film and multilayered piezoelectric actuators

Lead-free piezoelectric 0.885(Bi_0.5Na_0.5)TiO₃–0.05(Bi_0.5K_0.5)TiO₃–0.015(Bi_0.5Li_0.5)TiO₃ 0.05BaTiO₃ ceramics (abbreviated as BNKLBT-1.5) were prepared by a conventional mixed oxide method. The composition has a piezoelectric d₃₃ constant of 154 × 10⁻¹² C/N, an electromechanical coupling coefficient k_t of 0.519, a relatively low dissipation factor (tan δ = 1.6%) at 1 kHz. BNKLBT-1.5 multilayered actuators have been fabricated using a roll-casting technique. Each single layer has dimensions of 9.0 mm × 9.0 mm × 0.2 mm. Four multilayer actuators with 5, 10, 15 and 20 layers have been fabricated. Their capacitance and displacement under an a.c. field were measured. The capacitance measured at 1 kHz is 9.64 nF, 14.69 nF, 25.36 nF, 32.59 nF and the displacement measured at 5 kHz is 867 pm/V, 1331 pm/V, 2060 pm/V, 2442 pm/V, respectively.     

Polymer/piezoelectric ceramic composites: Polystyrene and poly(methyl methacrylate) with PZT

Lead zirconate–titanate (PZT)/polymer composites have been prepared by in situ polymerization of styrene and methyl methacrylate around aligned, thin PZT rods. Hydrostatic piezoelectric coefficients (d?_h and ?g_h) measured by a dynamic technique yielded figures of merit (d?_h?_h) roughly four times that of homogeneous PZT for as-polymerized composites. When these composites were annealed at a temperature slightly below the glass transition temperature of the matrix polymer and repoled, d?_h?_h increased nearly twofold due primarily to a reduction of the composite dielectric constant. The piezoelectric response was found to be essentially independent of frequency from 30 to 160 Hz.     

A low-cost multilayer piezoelectric actuator for ultrasonic motor stator driving fabricated by a low-temperature co-fired ceramic process

Multilayer piezoelectric ceramics have wide application prospects in the fields of precision driving and intelligent sensing owing to their low driving voltages and large strains. However, high sintering temperatures and expensive noble metal electrodes limit their application as multilayer piezoelectric ceramic actuators (MLAs) in conventional devices. In this study, a modified piezoelectric ceramic powder and Ag inner electrode were used to prepare a low-cost MLA with a low sintering temperature of 900 °C. The MLA showed superior piezoelectric properties with d₃₃ = 3015 pC/N and a large electric-field-induced strain of 0.13% at 22.2 kV/cm. Moreover, the stator of the ultrasonic motor composed of this MLA produced the ideal vibration mode, and the maximum rotation speed of the ultrasonic motor was 192 r/min under a 50 g load, which verifies the applicability of this component in practical minimised devices. These results demonstrate a strategy for fabricating low-cost and high-precision micro-actuators for precision driving.     

Processing and room temperature mechanical properties of a zirconium carbide ceramic

Zirconium carbide (ZrC) powder, batched to a ratio of 0.98 C/Zr, was prepared by carbothermal reduction of ZrO₂ with carbon black. Nominally phase-pure ZrC powder had a mean particle size of 2.4 μm. The synthesized powder was hot-pressed at 2150°C to a relative density of > 95%. The mean grain size was 2.7 ± 1.4 μm with a maximum observed grain size of 17.5 μm. The final hot-pressed billets had a C/Zr ratio of 0.92, and oxygen content of 0.5 wt%, as determined by gas fusion analysis. The mechanical properties of ZrC_0.92O_0.03 were measured at room temperature. Vickers’ hardness decreased from 19.5 GPa at a load of 0.5 kgf to 17.0 GPa at a load of 1 kgf. Flexural strength was 362.3 ± 46 MPa, Young's modulus was 397 ± 13 MPa, and fracture toughness was 2.9 ± 0.1 MPa•m^1/2. Analysis of mechanical behavior revealed that the largest ZrC grains were the strength-limiting flaw in these ceramics.     

Development of a model for the sintering of PZT multilayer ceramics and their dielectric properties

Piezoelectric multilayer ceramics are increasingly used in sophisticated applications for high-precision positioning systems. The reproducibility of the piezo-electrical properties is of major importance for the manufacture of high quality products. This study focuses on the variation of the sintering parameters and its effect on the poling behaviour as a contribution to the establishment of an understanding of PZT multilayer processing. To cover the complexity of the sintering process, the experiments were conducted with the design of experiments method. As parameters the sintering temperature, the holding time, the airflow in the furnace and the lead oxide atmosphere were investigated. As target variables the grain size, density and mass loss were investigated. In the following the correlations between the target variables and the sintering parameters were discussed and summarised in a model. The ceramic properties were correlated to the dielectric properties and the influence of the poling process was evaluated.     

Effect of heating rate on dielectric and pyroelectric properties of double doped PZT

Abstract

Double doped lead zirconium titanate (PZT) was synthesised by solid state reaction method. Calcination and sintering was carried out at various heating rates in order to study the effect of heating rate on the extent of phase formation of double doped PZT. Furthermore, the effect of heating rate on dielectric and pyroelectric properties was also investigated. Rhombohedral perovskite phase was confirmed in the double doped PZT samples. Quantitative X-ray diffraction (XRD) analysis suggests that the extent of PZT formation decreases beyond 8°C min^?1 heating rate. The crystallite and grain sizes calculated from Scherrer's equation and field emission scanning electron microscope (FE-SEM) photographs respectively show the decreasing behaviour with increasing heating rate. Dielectric and pyroelectric properties show the increasing behaviour up to 8°C min^?1 and decreasing behaviour beyond this heating rate.     

Achieving both large transduction coefficient and high Curie temperature of Bi and Fe co-doped PZT piezoelectric ceramics

Achieving both the large transduction coefficient (the product of piezoelectric charge d₃₃ and voltage coefficients g₃₃) and high Curie temperature is very important to improve the power generation performance and their thermal stability of piezoelectric energy harvesters. It is difficult to improve the transduction coefficient of the commercial PZT based piezoelectric ceramics due to the same variation trend of piezoelectric charge coefficient and dielectric constant with chemical modifications. In this work, Bi₂O₃ and Fe₂O₃ co-modified ((Pb_1-xBi_x)((Zr_0.53Ti_0.47)_1-xFe_x)O₃) ceramics were prepared by conventional solid state reaction method, and their dielectric and piezoelectric properties were studied. The piezoelectric charge coefficient d₃₃ increases by Bi and Fe co-modifications due to the enlarged grain size and reduced lattice distortion, while the dielectric constant ε₃₃ deceases mainly owing to the increased micro-pores in grains, leading to the enhancement transduction coefficient d₃₃×g₃₃. The Curie temperature Tc and maximum transduction coefficient d₃₃×g₃₃ are 346 °C and 17169 × 10^?15 m²/N, respectively, which are both higher than those of commercial PZT and PZN-PZT based piezoelectric ceramics. This work provides a new way to enhance the transduction coefficient of PZT based ceramics for piezoelectric energy harvesters used in wide temperature range.     

Effect of tungsten on the structure and piezoelectric properties of PZN–PZT ceramics

0.2PZN–0.8PZT ceramics with pure perovskite structure were prepared by the two-step method with the addition of 0–1.5 wt.% WO₃ and their piezoelectric properties were investigated. The WO₃ addition influences the lattice structure and W⁶⁺ will replace B-site ions of perovskite, which will lead to the decrease of the lattice constant. Compared to the increase of the dielectric constant (ɛ) and mechanical quality factor (Q_m), the values of coercive electric field (E_c), remnant polarization (P_r), electromechanical coupling factor (K_p), and piezoelectric constant (d₃₃) decrease with increasing WO₃ addition. The composition with 1.0 wt.% of WO₃ addition on 0.2PZN–0.8PZT ceramics exhibits excellent piezoelectric properties, showing great promise as practical materials for high power piezoelectric devices.     

Dielectric and piezoelectric properties of PVDF/PZT composites: A review

Smart materials, which exhibit piezoelectricity, find an eclectic range of applications in the industry. The direct piezoelectric effect has been widely used in sensor design, and the inverse piezoelectric effect has been applied in actuator design. Ever since 1954, PZT and BaTiO₃ were widely used for sensor and actuator applications despite their toxicity, brittleness, inflexibility, etc. With the discovery of PVDF in 1969, followed by development of copolymers, a flexible, easy to process, nontoxic, high density alternate with high piezoelectric voltage coefficient was available. In the past 20 years, heterostructural materials like polymer ceramic composites, have received lot of attention, since these materials combine the excellent pyroelectric and piezoelectric properties of ceramics with the flexibility, processing facility, and strength of the polymers resulting in relatively high dielectric permittivity and breakdown strength, which are not attainable in a single phase piezoelectric material. The current review article is an attempt to provide a compendium of all the work carried out with reference to PVDF‐PZT composites. The review article evaluates the effect of grain size, content and other factors under the purview of dielectric and piezoelectric properties while evaluating the sensitivity of the material for sensor application. POLYM. ENG. SCI., 55:1589–1616, 2015. © 2015 Society of Plastics Engineers