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 temperature on aging degradation of soft and hard lead zirconate titanate ceramics

This paper aims to study the effects of heat treatment temperatures on the aging degradation of piezoelectric properties, i.e. piezoelectric coefficient (d₃₃) and planar electromechanical coupling factor (k_p), in soft and hard PZT ceramics. Aging degradations of d₃₃ and k_p of the samples were measured for 192 h prior to heat treatments. The samples were then treated at various temperatures equivalent to 0.3, 0.4, 0.5, 0.6, 0.7 and 0.8 times of the materials' Curie temperatures. Aging degradations of d₃₃ and k_p of the heat-treated samples were observed continuously for 1128 h. The piezoelectric properties of the un-treated samples gradually decreased with aging time. Attenuation of d₃₃ and k_p in the samples immediately after heat treatment increased with increasing heat treatment temperature. Moreover, aging degradation rate and relaxation time of the samples measured after heat treatments increased with increasing heat treatment temperature. Comparing to hard PZT ceramics, soft PZT demonstrated greater change of d₃₃ and k_p immediately after heat treatments. Soft PZT also showed greater aging rate and aging time than those of hard PZT. From the overall results, it can be concluded that both material type and heat treatment temperature have effects on aging behaviors of PZT materials. Aging degradation was more pronounced in soft PZT and the samples treated at high temperatures. The observed aging behaviors of PZT materials were explained by the interaction between domains and defects of oxygen vacancies that leads to volume, domain and grain boundary effects.     

Features of the structure and macro responses in hard ferro piezoceramics based on the PZT system

The structure, microstructure, dielectric and piezoelectric properties of two ferroelectric materials based on the modified PbTiO₃-PbZrO₃ (PZT) system, prepared using the conventional ceramic technology and hot pressing method have been studied, and correlations among their elemental composition, phase constitution, grain structure and macro responses have been investigated. Specific features of ferroelectric-paraelectric phase transitions during the variation of the frequency of an alternating electric field (in the interval of 25?Hz ÷ 2?MHz) have been singled out. It was shown that the properties of samples produced without an externally applied pressure are not lower than those of the hot pressed samples thus allowing their perspective use in frequency-selective devices such as variable bandwidth filters.     

High-strain piezoelectric ceramics and applications to actuators

PZT-based solid solutions are very attractive piezoelectric ceramics, because they exhibit excellent piezoelectric properties such as large piezoelectric constant. In this paper we describe the relationship between piezoelectric properties and compositions, and sintering behavior of PbNiNbTiO₃–PbTiO₃–PbZrO₃ (PNN–PT–PZ) ceramics and applications to the microactuators for magnetic disk drives. The MPB composition was determined by the temperature dependence of the relative permittivity and XRD patterns. The large piezoelectric constant (d₃₃ = 1100 pm/V) was obtained at the MPB composition. Unique rotating symmetrical microactuators using PNN–PT–PZ ceramics show both wide stroke and high-resonant frequency. In this paper we also describe the applications of piezoelectric ceramics to tunable superconductive filters for future wireless communication systems. Low-temperature piezoelectric properties of PZT-based ceramics and frequency tunable mechanisms will be discussed. This work was supported in part by the Ministry of Internal Affairs and Communications (MIC) of Japan.     

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.     

Influence of hydrothermal synthesis conditions on BNT-based piezoceramics

The Bi_0.5Na_0.5TiO₃ perovskite (BNT) is a very promising lead-free candidate for piezoelectric applications. Nevertheless a low reproducibility is commonly reported for the solid state synthesized BNT. In this work, the hydrothermal synthesis was investigated to improve the BNT ceramics characteristics reproducibility. The synthesis conditions were studied in order to control more particularly the BNT grain size, crystallinity and stoichiometry.Thanks to the slow hydrolysis of titanium isopropoxide with bismuth nitrate pentahydrate, well crystallized BNT-based powder was synthesized at 265 °C. Nevertheless this powder exhibited secondary amorphous phases. Such secondary phases synthesis was limited and prevented by both lowering the temperature synthesis down to 160 °C and optimizing the washing conditions of the powder. The BNT was finally made free of any amorphous phase by using a hydrochloric solution. The BNT sinterability was improved and BNT-based piezoceramics exhibiting a d₃₃ as high as 60 pC/N were successfully produced.     

Domain wall-grain boundary interactions in polycrystalline Pb(Zr0.7Ti0.3)O3 piezoceramics

Interactions between grain boundaries and domain walls were extensively studied in ferroelectric films and bicrystals. This knowledge, however, has not been transferred to polycrystalline ceramics, in which the grain size represents a powerful tool to tailor the electromechanical and dielectric response. Here, we relate changes in dielectric and electromechanical properties of a bulk polycrystalline Pb(Zr_0.7Ti_0.3)O₃ to domain wall interactions with grain boundaries. Samples with grain sizes in the range of 3.9–10.4 μm were prepared and their microstructure, crystal structure, and dielectric/electromechanical properties were investigated. A decreasing grain size was accompanied by a reduction in large-signal electromechanical properties and an increase in small-signal relative permittivity. High-energy diffraction analysis revealed increasing microstrains upon decreasing the grain size, while piezoresponse force microscopy indicated an increased local coercive voltage near grain boundaries. The changes in properties were thus related to strained material volume close to the grain boundaries exhibiting reduced domain wall dynamics.     

Low-temperature sintering of (K,Na)NbO3-based lead-free piezoceramics with addition of LiF

Dense Li/Ta-codoped KNN-based piezoceramics with d₃₃^* up to 375 pm/V were successfully fabricated by conventional sintering at a temperature as low as 900 °C by using LiF as a sintering additive. The reduction of densification temperature up to 200 °C was realized by a transient liquid phase sintering mechanism, consequently no grain boundary phase was observed in the sintered samples. It was found that the addition of LiF could further shift down the tetragonal–orthorhombic transition point (T_T-O), indicating that a small amount of Li⁺ could diffuse into the A-site of KNN matrix. The introduction of LiF enhanced the linearity of strain curves of the ceramics, which is unambiguously in favor for the actuator application. The present work reveals that low-temperature sintered LiF-doped KNN-based piezoceramics demonstrates promising potential in multilayer-structured actuator applications.     

Effects of pore size and orientation on dielectric and piezoelectric properties of 1-3 type porous PZT ceramics

Porous PZT ceramics have drawn an increasing amount of interest in recent years due to their superior properties compared with the dense material. However, researchers have usually dedicated effort to 0-3 and 3-3 type porous PZT ceramics and little attention has been focused on 1-3 type. The 1-3 type porous PZT ceramics with high porosity were fabricated in this study by freeze-casting process. All samples possessed high piezoelectric coefficient (d₃₃) with high porosity owing to the special one-dimensional ordered porous structure along the poling direction. The d₃₃ values increased by either improving the pore channel orientation level or decreasing pore size. The relative permittivity improved only with the enhancement of pore channel orientation level. The acoustic impedances ranged from 1.45 to 1.35 MRayls which could match well with those of biological tissue or water; therefore, this material would be beneficial in hydrophone applications.     

Monomorph piezoelectric wideband energy harvester integrated into LTCC

In this paper the first fully LTCC embedded piezoelectric vibration harvester is demonstrated and characterized. Using ordinary LTCC processes a 39 mm × 39 mm × 3 mm package containing 25 mm co-fired PZT discs was made. Three laser cut beams of different lengths provided a 5.4% frequency bandwidth for 3 dB attenuation and a power of 32 μW at 1 g acceleration delivered into a 33.9 kΩ resistive load. The packaged structure was compared to a bare monomorph reference sample and showed less crosstalk, better frequency control and more power generated. The experiments showed that integration of LTCC and PZT bulk materials by co-firing is a very feasible way to realise energy harvesters for wireless technologies, sensors and autonomous System-On-a-Package.     

Improved piezoelectric properties of Pb(Zr0·70Ti0.30)O3 ceramics doped with non-polar bismuth manganite

This report documents the electrical features of (1-x) Pb(Zr_0·70Ti_0.30)O₃–x BiMn₂O₅ ceramics with x = 0–0.05 (PZT–BM). A structural disorder was introduced by doping with non-polar bismuth manganite (BM) to increase the chemical disorder in PZT ceramics, which is one of the reasons for its marked piezoelectric properties. The chemical disorder was confirmed using scanning electron microscopy. The rhombohedral symmetry of a crystal lattice was determined using the XRD powder test. To assess the influence of BM dopant on the electric properties of PZT, dielectric spectroscopy was performed at a frequency f = 1 kHz–1 MHz and in a temperature range of 290–680 K. Several effects on the dielectric characteristics were induced by the addition of BM, including the shift and diffuseness of the transition from the ferroelectric to the paraelectric phase and the diffuseness of the transition between two ferroelectric phases. The electrical conductivity increased as the BM content increased. Piezoelectric studies have shown that 0.99 PZT–0.01 BM ceramics exhibit better piezoelectric properties and higher permittivity than pure PZT ceramics. The 0.99 PZT–0.01 BM piezoelectric coefficient d₃₃ increased by approximately 30% compared with pure PZT.     

Study of vibratory behavior of interconnected porous PZT by impulse method

Performances in ultrasonic active transducers of interconnected porous lead zirconate titanate (PZT) piezoelectric disks with a porosity ranging from 30 to 70%, and polarized along their axial axis, are investigated. The characterization method used is based on the measurement of the voltage, which appears between the two faces of the piezoelectric element when it is excited by a current impulse. The device used, allows the acquisition of axial and radial vibrations of the transducer, and from these data, electromechanical and acoustic parameters are deduced. One observes that interconnected porosity causes the disappearance of the radial vibrations, and for large porosities the disk vibrates exclusively according to the axial mode. k_t is increased, the acoustic impedance is reduced, and the axial propagation velocity reaches 2500 m s⁻¹ for 30% of porosity. These results show that interconnected porous PZT are suitable for making ultrasonic active transducer, such as biomedical imaging devices.     

Impact of ionizing radiation on structural,dielectric, and piezoelectric properties of Sr modified PZT

Ion irradiation effects on piezoceramic (Pb_0.94 Sr_0.04) (Zr_0.52 Ti_0.48)O₃ (PSZT) are investigated by using 4 MeV carbon (C), 9 MeV copper (Cu), and 20 MeV gold (Au) ions. The energies of incident ions are selected in order to target the same range of all incident ions in the material, while producing different amounts of vacancies. The ion irradiation is performed with fluences of 1×10¹³, 1×10¹⁴, and 1×10¹⁵ ions/cm² using Tandem Pelletron accelerator (5UDH-2). Post irradiation changes in PSZT are investigated via various structural, dielectric, and piezoelectric measurement techniques. Results divulge that the irradiation process disturbs the crystallinity along with reduction in X-ray diffraction (XRD) peak intensities owing to strain induced structural defects. A small decrease in dielectric constant is observed due to trapped charges, which screen the depolarization after irradiation. However, a significant decrease is detected in piezoelectric charge coefficients (d₃₃) and piezoelectric voltage coefficients (g₃₃) due to switching of micro domains of PSZT as a result of energy observed during irradiation process. These results indicate that ion irradiation has damaging effects on the properties of PSZT. The discussed information may be utilized to assess performance of PSZT based devices under radiation rich environments such as space.     

Effect of sintering aid and repeated sol infiltrations on the dielectric and piezoelectric properties of a PZT composite thick film

Thick PZT films have been produced using a combination of spin coating of a composite slurry and subsequent infiltration of PZT producing sol. The effect of adding a Cu₂O–PbO sintering aid and repeated sol infiltrations have been studied with the aim of producing dense PZT films. Relative permittivity has been shown to increase with the addition of sintering aid and increased levels of sol infiltration. Measurements of piezoelectric properties indicate that sol infiltrations have no effect on d₃₃ once a critical density has been exceeded. A sample with approximately 10% closed porosity was obtained following the incorporation of sintering aid and four infiltration steps per layer. This resulted in a mean relative permittivity of approximately 700 and a d₃₃ of 62 pC/N (poling conditions: 8 V/μm for 5 min at 200 °C).     

Microstructure and electric properties of Pr-doped Pb(Zr0.52Ti0.48)O3 ceramics

Improving the piezoelectric activity of lead zirconate titanate (PZT) ceramics is of great importance for practical applications. In this study, the influence of Pr³⁺ doping on the ferroelectric phase composition, microstructure, and electric properties on the A-site of (Pb_1-1.5xPr_x)(Zr_0.52Ti_0.48)O₃ is extensively investigated. A dense and fine microstructural sample is obtained with the introduction of Pr³⁺. The results show that the morphotropic phase boundary (MPB) moves to the rhombohedral phase region. The rhombohedral and tetragonal phases exhibit an ideal coexistence in the 4 mol.% Pr³⁺ doped (PPZT4) samples. Lead vacancy and the reduction of the potential energy barrier are considered to be the key mechanisms for donor doping, which is upheld by the Pr³⁺ doping. Combining the I-E hysteresis loops with the P-E hysteresis loops, it becomes apparent that both contribution maximums of the domain switching and residual polarisation are in PPZT4. Moreover, the thermal aging resistance of PZT is improved by doping, and the temperature stability is optimised from 83% in PZT to 96% in PPZT4. Hence, an appropriate amount of Pr³⁺ doping can effectively improve the piezoelectric activity of PZT ceramics in the MPB area and optimise the performance stability of the material under application temperatures.     

Effect of the slurry composition on the piezoelectric properties of PZT ceramics fabricated via materials extrusion 3D printing

Herein, the effect of the binder content in lead zirconate titanate (PZT) slurry has been systematically studied to improve the piezoelectric properties of PZT ceramics prepared via material extrusion 3D printing. For smooth printing, a slurry with a binder concentration ranging from 6 to 12 wt% was proposed. The porosity of the green body first decreased and then increased with an increase in the binder concentration, and the minimum porosity was obtained when the binder concentration reached 10 wt%. Samples with increased density were obtained after debinding and lead-rich atmosphere sintering. PZT piezoceramics fabricated using a binder content of 10 wt% exhibit the maximum relative density (96.9%), largest piezoelectric constant (342.6 pC/N) and dielectric constant (1621). Based on the above process, the wood pile structure and helical twentytetrahedral structural components were successfully fabricated using the material extrusion process. This research lays the foundation for the engineering application of 3D printing to fabricate high-performance piezoceramics with complex shapes.     

Progress and challenges of 3D-printing technologies in the manufacturing of piezoceramics

Piezoceramic materials provide the foundation for essential components of modern engineering applications in the fields of acoustics, sensorics, biomedical devices, and microelectronics. With device miniaturization, the industrial requirements for piezoceramics with complex geometries and improved efficiencies has grown tremendously. Traditionally manufactured piezoceramics demonstrate great piezoelectric properties but poor shape conformity. Additive manufacturing (AM) technologies, being a successful contender in the field of technical ceramics, makes its way into piezoceramics production. AM technology applied to traditional piezoelectric materials has many obstacles to overcome, since typical piezoceramic products require complex and intricate shapes, and often consist of composite materials. As a solution to these problems, AM technology can be transformed into a robust fabrication tool. This review intends to outline the current state of the art of AM technologies applied to the manufacture of piezoceramic materials. Modern piezoceramic materials are described in detail, including the effects of doping and texturing. The properties of piezoceramics and their composites are compared for traditionally and additively manufactured devices. The piezolectric properties of the materials produced using different manufacturing methods are summarized in comprehensive tables and figures, where the emerging trends in physical characteristics are revealed. The pros and cons of AM technologies are discussed, and the problems to be addressed in future work are highlighted.     

Effects of slurry composition on the properties of 3-1 type porous PZT ceramics prepared by ionotropic gelation

In this study, 3-1 type lead zirconate titanate (PZT) ceramics with one-dimensional pore channels were produced by ionotropic gelation process of alginate/PZT suspensions. By increasing the sodium alginate concentration from 1.0wt% to 3.0 wt%, the alginate/PZT suspensions turned from Newtonian to non-Newtonian behavior with substantial increase in apparent viscosity. Accordingly, 3-1 type PZT ceramics with porosity decreasing from 56.78% to 41.44% were obtained, while the pore size distribution became non-uniform gradually. Based on the structural features, the 3-1 type PZT ceramics possessed much higher relative permittivity (ε_r) than that of 3-0 or 3-3 type PZT ceramics with similar porosities. Increase in the porosity led to a moderate decline in the longitudinal piezoelectric strain coefficient (d₃₃), a reduction in the dielectric loss factor (tan δ), and a high value of hydrostatic strain coefficient (d_h). As a result, the 3-1 type PZT ceramics possessed a maximal hydrostatic figure of merit (HFOM) value of 5597×10^–15 Pa⁻¹ when the porosity was 56.78%, which may be of help for low frequency hydrophones applications.     

Degradation of α-linolenic acid during heating

Degummed bleached rapeseed oil was heated at 210, 220, and 230°C for up to 86 h under reduced pressure with nitrogen stripping. No significant change of total linoleic acid content was found, but a decrease of the total linolenic acid content was observed under extreme conditions. The degradation rate of linolenic acid is described as a function of heating time and operating temperature. Linolenic acid degradation can be predicted for any set of conditions by the established model. No significant degradation of linolenic acid can occur under standard deodorization conditions. Lesieur and Cereol are divisions of Eridania Béghin-Say Group.     

Phase transition and piezoelectric properties of lead-free (Bi1/2Na1/2)TiO3–BaTiO3 ceramics

(1−x)(Bi_0.5Na_0.5)TiO₃–xBaTiO₃ ceramics (x=0.03, 0.06, 0.08, 0.12, 0.15, 0.20, 0.30, 0.40, 0.50, 0.60, 0.70, 0.80, and 0.90) were fabricated by a conventional solid-state reaction and their phase transitions and piezoelectric properties were investigated using XRD analyses, Curie temperature, the frequency dependance of dielectric constant, and P–E curves. A complete solid solution with a perovskite structure was formed in the whole composition range of BNT–BT and more than two phase transitions arising from a compositional change were found. With increasing BaTiO₃ content, the sequence of phase transitions from a rhombohedral structure to unknown tetragonal structures and finally a tetragonal structure with the space group P4mm has been established. While the rhombohedral–tetragonal phase transition led to superior piezoelectric properties in BNT–BT ceramics, other phase transitions between tetragonal structures had a little effect on piezoelectric properties. The d₃₃, ε_r, k_p, k_t, and Q_m and values lied in ranges of 40–130 pC/N, 400–900, 10–30%, 15–30%, and 50–250, respectively.