Porous Piezoelectric Ceramics Research Articles

Piezoelectric ceramics with hierarchical macro- and micro-pore channels for sensing applications

Piezoelectric sensors have attracted increasing attention due to their high sensitivity to forces, pressures and acceleration. The use of porous piezoelectric ceramics with aligned pores formed by freeze casting for sensing application also exhibit advantages due to their combination of a high piezoelectric charge coefficient and low permittivity, which leads to an enhancement in sensor sensitivity compared to dense materials. To fabricate porous materials, the process of direct ink writing (DIW) exhibits superiority in terms of structural design as a result of its ability to provide layer-by-layer and mold-free rapid prototyping. This work provides the first demonstration of the fabrication of lead zirconate titanate (PZT) piezoelectric ceramic scaffolds with sophisticated hierarchical porous structures by simultaneous DIW and freeze casting. The morphology of the porous cells and individual layers of the hierarchical porous PZT ceramic scaffolds were designed by adjusting the rheological properties and optimizing the printing path. The effect of cell structure and number of layers on sensing performance was investigated in detail. Manufactured scaffolds with a sandwich structure exhibited a high output voltage (191 V) under the application of 1 N external force, with a sensitivity of 8.98 V·kPa−1. This work provides a new approach to structural design of piezoelectric sensors to inform future efforts in the fabrication of high-performance piezoelectric ceramics with hierarchical porosity with complex and bespoke geometries.

Effect of solid content on the piezoelectric properties of porous (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 ceramics

The influence of the solid content of porous (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 (BCZT) ceramics on the pore morphology and mechanical and piezoelectric properties was systematically investigated. The results show that with an increase in solid content, porosity and pore size decreased, and ceramic connectivity increased, leading to an increase in compressive strength. The best ferroelectric performance was achieved with an Ec of 2.40 kV/cm2 and a Pr of 2.01 μC/cm2 at a solid content of 30 vol%. When the solid content increased, the relative dielectric constant and the piezoelectric constant increased, which affected the piezoelectric energy harvesting performance. At a solid content of 20 vol%, g33 and FOM33 reached maxima of 43 × 10−3 Vm/N and 6.7 p.m.2/N, which were 2.40 times and 1.8 times those of the other solid contents, respectively. This work provides new ideas for the design of porous piezoelectric ceramics and the improvement of their piezoelectric properties for future piezoelectric energy harvesting applications.

Kirigami-Origami-Inspired Lead-Free Piezoelectric Ceramics.

Kirigami- and oirigami-inspired techniques have emerged as effective strategies for material structure design; however, the use of these techniques is usually limited to soft and deformable materials. Piezoelectric ceramics, which are typical functional ceramics, are widely used in electronic and energy devices; however, the processing options for piezoelectric ceramics are limited by their brittleness and feedstock viscosity. Here, a design strategy is proposed for the preparation of lead-free piezoelectric ceramics inspired by kirigami/origami. This strategy involves direct writing printing and control over the external gravity during the calcination process for the preparation of curved and porous piezoelectric ceramics with specific shapes. The sintered BaTiO3 ceramics with curved geometries produced using this strategy exhibit a high piezoelectric constant (d33 = 275 pCN-1 ), which is 45% higher than that of conventionally sintered sheet ceramics. The curved structure of the ceramics is well-suited for use in the human body and itwasdetermined that these curved ceramics can detect pulse signals. This strategy can be applied in the large-scale and low-cost production of other piezoelectric ceramics with various curved shapes and provides a new approach for the preparation of complex-shaped ceramics.

Enhanced energy harvesting performance in lead-free multi-layer piezoelectric composites with a highly aligned pore structure

The harvesting of mechanical energy from our living environment via piezoelectric energy harvesters to provide power for next generation wearable electronic devices and sensors has attracted significant interest in recent years. Among the range of available piezoelectric materials, porous piezoelectric ceramics exhibit potential for both sensing and energy harvesting applications due to their reduced relative permittivity and enhanced piezoelectric sensing and energy harvesting figures of merit. Despite these developments, the low output power density and the lack of optimized structural design continues to restrict their application. Here, to overcome these challenges, a lead-free multi-layer porous piezoelectric composite energy harvester with a highly aligned pore structure and three-dimensional intercalation electrodes is proposed, fabricated and characterized. The effect of material structure and multi-layer configuration of the porous piezoelectric ceramic on the dielectric properties, piezoelectric response and energy harvesting performance was investigated in detail. Since the relative permittivity is significantly reduced due to the introduction of aligned porosity within the multi-layer structure, the piezoelectric voltage coefficient, energy harvesting figure of merit and output power are greatly enhanced. The multi-layer porous piezoelectric composite energy harvester is shown to generate a maximum output current of 80 μA, with a peak power density of 209 μW cm−2, which is significantly higher than other porous piezoelectric materials reported to date. Moreover, the generated power can charge a 10 μF capacitor from 0 V to 4.0 V in 150 s. This work therefore provides a new strategy for the design and manufacture of porous piezoelectric materials for piezoelectric sensing and energy harvesting applications.

Perspective on Porous Piezoelectric Ceramics to Control Internal Stress

Due to the unique electromechanical energy conversion capability of ferroelectric materials, they have been at the forefront of materials science for a variety of applications such as sensors, actuators and energy harvesting. Researchers have focused on exploring approaches to achieve improved ferroelectric performance, and to ensure that the available material systems are more environmentally friendly. This comprehensive review summarizes recent research progress on porous ceramics and highlights the variety of factors that are often ignored, namely the influence of porosity on the Curie temperature, and applications of porous ferroelectric materials with adjustable Curie temperature. Finally, the development trends and challenges of porous ferroelectric materials are discussed, aiming to provide new insights for the design and construction of ferroelectric materials.

Microstructural features and complex electromechanical parameters of Pb0.95Sr0.05Ti0.47Zr0.53O3 + 1% Nb2O5 porous piezoceramics

In this article, a correlation between microstructure and properties for porous piezoceramics of the composition Pb0.95Sr0.05Ti0.47Zr0.53O3 + 1% Nb2O5 was studied in detail. Experimental samples of porous piezoceramics were obtained using a modified method of burning-out a pore former. Porosity dependences of dielectric, elastic, piezoelectric, and electromechanical coefficients of the porous ceramics in the relative porosity range 0–50% were measured and analyzed. It was revealed that the microstructural features of porous piezoceramics defined the character of the porosity dependences of the dielectric, piezoelectric, and electromechanical properties of porous piezoelectric ceramics.

Ultrasonic Transducers Made From Freeze-Cast Porous Piezoceramics.

Porous and composite piezoelectric ceramics are of interest for underwater ultrasonic transducers due to their improved voltage sensitivity and acoustic matching with water, compared with their dense counterparts. Commonly, these materials are fabricated by dice-and-fill of sintered blocks of polycrystalline piezoceramic, which results in a high volume of waste. The freeze-casting technique offers a low waste and scalable alternative to the dice-and-fill method to produce porous piezoceramics with highly orientated, anisometric pores. In this article, we have fabricated underwater ultrasonic transducers from freeze-cast lead zirconate titanate (PZT) with a range of porosities. The porous PZT samples were characterized in terms of their piezoelectric and dielectric properties before being encapsulated for acoustic performance testing in water. Off resonance, the on- axis receive sensitivity of the manufactured devices was approximately [Formula: see text]; the transmit voltage response (TVR) was in the range of approximately [Formula: see text] at 60 kHz to [Formula: see text] at 180 kHz. The most porous transducer devices (0.51, 0.43, and 0.33 pore fraction) exhibited primarily a thickness mode resonance, whereas the least porous transducers (0.29 pore fraction and dense benchmark) exhibited an undesired radial mode, which was observed as an additional resonant peak in the electrical impedance measurements and lateral off-axis lobes in the acoustic beampatterns. Our results show that the acoustic sensitivities and TVRs of the porous freeze-cast transducers are comparable to those of a dense pressed transducer. However, the freeze-cast transducers with porosity exceeding 0.30 pore fraction were shown to achieve an effective structure with aligned porosity that suppressed undesired radial mode resonances.

Evaluation of the pore morphologies for piezoelectric energy harvesting application

Piezoelectric energy harvesting has attracted significant attention in recent years due to their high-power density and potential applications for self-powered sensor networks. In comparison to dense piezoelectric ceramics, porous piezoelectric ceramics exhibit superiority due to an enhancement of piezoelectric energy harvesting figure of merit. This paper provides a detailed examination of the effect of pore morphology on the piezoelectric energy harvesting performance of porous barium calcium zirconate titanate 0.5Ba(Zr 0.2 Ti 0.8 )O 3 -0.5(Ba 0.7 Ca 0.3 )TiO 3 (BCZT) ceramics. Three different pore morphologies of spherical, elliptical, and aligned lamellar pores were created via the burnt-out polymer spheres method and freeze casting. The relative permittivity decreased with increasing porosity volume fraction for all porous BCZT ceramics. Both experimental and simulation results demonstrate that porous BCZT ceramics with aligned lamellar pores exhibit a higher remanent polarization. The longitudinal d 33 piezoelectric charge coefficient decreased with increasing porosity volume fraction for the porous ceramics with three different pore morphologies; however, the rate of decrease in d 33 with porosity is slower for aligned lamellar pores, leading to the highest piezoelectric energy harvesting figure of merit. Moreover, the peak power density of porous BCZT ceramics with aligned lamellar pores is shown to reach up to 38 μW cm -2 when used as an energy harvester, which is significantly higher than that of porous BCZT ceramics with spherical or elliptical pores. This work is beneficial for the design and manufacture of porous ferroelectric materials in devices for piezoelectric energy harvesting applications.

3D printing of porous scaffolds BaTiO3 piezoelectric ceramics and regulation of their mechanical and electrical properties

A series of porous scaffolds of piezoelectric ceramic barium titanate (BaTiO3) were successfully fabricated by Digital Light Processing (DLP) 3D printing technology in this work. To obtain a high-precision and high-purity sample, the debinding sintering profile was explored and the optimal parameters were determined as 1425 °C for 2h. With the increase of scaffolds porosity from 10% to 90%, the compressive strength and piezoelectric coefficient (d33) decreased gradually. The empirical formulas about the mechanical and piezoelectric properties were obtained by adjusting BaTiO3 ceramics with different porosity. In addition, the distribution of potential and stress under 100 MPa pressure were studied by the finite element method (FEM).

Effect of different pore formers on the performance of lead free piezoelectric ceramics

Ceramics based piezoelectric materials with unique porous microstructure and chemical compositions are regarded suitable for advanced applications due to their distinct properties. In this work, NKN-ST [(1-x) (Na0.5 K0.5 NbO3)—x (SrTiO3)] specimens were prepared by conventional solid-state method. Using different pore forming agents such as ammonium oxalate monohydrate and graphite, porous piezoelectric ceramics were processed to obtain different porous configuration by sacrificial foaming method. Scanning electron microscopy showed a continuous structure with interconnectivity. The phase structure, dielectric and piezoelectric properties of the samples were systematically investigated on the effects upon addition of SrTiO3 content and different porogens.

Ferroelectric domain formation and photocatalytic activity on porous alkali niobate piezoelectric ceramics

Present study showed synthesis of novel type of porous alkali niobate piezoelectric ceramics, and the formation of domains and photocatalytic activity for the porous piezoelectric ceramics were investigated while comparing with dense ceramics to confirm enhancement of domain orientation and photocatalytic activity around pores. Porous Li0.06Na0.47K0.47NbO3 piezoelectric ceramics were synthesized by a template method using polymethylmethacrylate as a pore former agent. Uniform pores with 6 µm in diameter were dispersed in the porous ceramics. Porous ceramics synthesized with 10 vol % of the pore former agent showed piezoelectric voltage coefficient, 29 mVm/N, which is same as that of the dense ceramics. Smaller striped domains formed at an edge of pores on the porous ceramics, indicating that orientation of domains was promoted by electric field concentration around the pores. Through photoreduction reaction of Ag+ ion, local precipitation of Ag was shown around the pores on the poled porous ceramics, whereas Ag was located over an entire surface of unpoled porous ceramics. Highest photocatalytic activity was shown for the poled porous ceramics in photodecomposition test of methylene blue. These results clearly indicated photocatalytic activity was enhanced on ferroelectric domains around pores of porous piezoelectric ceramics.

Microstructure characterization and properties of porous piezoceramics

In this paper, a comprehensive study of microstructure/properties interrelations for porous piezoceramics based on PZT composition was performed. Experimental samples of porous piezoceramics were fabricated using a modified method of burning-out a pore former. Porosity dependencies of elastic, dielectric, piezoelectric and electromechanical coefficients of the porous ceramics in the relative porosity range 0-50% were obtained and analyzed. As a result of microstructure analysis, it was found that at any connectivity type (3–0, 3–3) and porosity up to 50% the real structures of porous piezoceramics were close to the matrix medium structure with continuous piezoceramic skeleton. It was also revealed that the microstructural features of porous piezoceramics define the character of the dependences of the dielectric, piezoelectric and electromechanical properties of porous piezoelectric ceramics on porosity. In conclusion, microstructure/properties interrelations, as well as new applications of porous piezoceramics were discussed.

Dispersion characteristics of complex electromechanical parameters of porous piezoceramics

In this paper, the results of experimental study of dispersion characteristics of complex electromechanical parameters of ferroelectrically “hard” porous piezoceramics based on PZT composition were presented. Experimental samples of porous piezoceramics were fabricated using a modified method of burning-out a pore former. The complex constants of porous piezoceramics with relative porosity 16% and their frequency dependences were measured using the piezoelectric resonance analysis method. As a result of experimental studies, regions of elastic, piezoelectric and electromechanical dispersion, characterized by anomalies in the frequency dependences of the imaginary and real parts of the complex constants of porous piezoelectric ceramics were found. It was revealed also that the microstructural features of porous piezoceramics determine the character of frequency dependences of complex electromechanical parameters of porous piezoelectric ceramics. In conclusion, the microstructural and physical mechanisms of electromechanical losses and dispersion in porous piezoceramics were discussed.

Electromechanical properties of ultra‐low porous auxetic piezocomposite: from the perspective of Poisson’s ratio

AbstractIn this study, the ultra‐low porous auxetic piezoelectric composite made of lead zirconate titanate (PZT) and hollow polyvinylidine difluoride (PVDF) is first proposed by combining “additive” and “subtractive” approaches. The electromechanical properties of the auxetic piezoelectric composite are investigated by finite element analysis. It is found that the ultra‐low porosity in the composite may lead to great extensibility along with the excellent figures of merit obtained in conventional highly porous piezoelectric ceramics. The small amount of additional PVDF can greatly tune the electromechanical properties of composite and effectively reduce the maximum stress of PZT. To elucidate the role of Poisson’s ratio on the electromechanical properties of piezoelectric materials, the relationship expressions among some electromechanical coefficients are derived. Moreover, the semi‐empirical expression of “longitudinal” compliance coefficients and a simple strategy for predicting some electromechanical coefficients are presented to instruct design and application of the ultra‐low porous auxetic piezoelectric materials.

Numerical analysis of the effective properties of inhomogeneously polarized porous piezoelectric ceramics with ni-doped pore walls taking into account the influence of volume fractions of metal and pores

The paper considers a porous piezoelectric composite with metal layers deposited on the interface between the piezoelectric and vacuum phases. Such metal layers can be added technologically to improve the mechanical and electromechanical properties of the composite. To find the effective moduli, we designed a simple representative cubic volume of a unit cell consisting of a piezoelectric matrix with a compound spherical pore in its center. In turn, the compound pore includes the pore itself and a hollow metal sphere on its surface. The composite's three phases were all modeled as piezoelectric materials. The conducting interface layer was modeled as a piezoelectric material with very high dielectric constants, small piezoelectric moduli, and elastic properties of the employed metal, while the vacuum pore was modeled as a piezoelectric material with marginal moduli. The mathematical formulation of boundary value homogenization problems with full contact conditions on the interface boundaries, based on the Hill energy criterion, was described. By solving nine boundary value problems of electroelasticity with different boundary conditions for displacements and electric potential by the finite element method, a complete set of effective moduli of the piezoelectric composite is determined. The importance of considering the inhomogeneous polarization due to the presence of pores and metallic inclusions was discussed. An approximate method was proposed for determining the inhomogeneous polarization field in a piezoceramic matrix, based on a preliminary solution of the electrostatic problem for dielectrics and locating the element coordinate systems rotated along the polarization vector. The paper describes the results of computational experiments for a piezocomposite consisting of PZT-5H piezoceramic matrix, pores, and nickel layers on the pore surfaces. Comparisons between the effective properties of this composite with different volume fractions of metal and the conventional porous piezocomposite were provided, depending on the porosity and taking into account the inhomogeneous polarization. Significant differences were observed for some piezomoduli and dielectric constants, which are promising for various practical applications of the considered composites in piezoactuators using the phenomenon of the transverse piezoelectric effect.

Highly tailorable electromechanical properties of auxetic piezoelectric ceramics with ultra‐low porosity

AbstractConventional porous piezoelectric ceramics can possess superior figures of merit only at very high values of porosity, leading to bad fragileness, small stiffness, low toughness, and the difficulty of polarization. To this end, this study for the first time shows that it is possible that the piezoelectric ceramic with ultra‐low porosity is capable of superior figures of merit based on the concept of auxetic piezoelectric ceramics. Owing to the ultra‐low porosity and auxetic effect, the auxetic piezoelectric ceramic shall also possess larger stiffness, higher toughness, and is more easily polarized. First, the auxetic piezoelectric ceramic with ultra‐low porosity is proposed to achieve highly tunable electromechanical properties on the basis of the rotating square mechanism. Then, using a multiscale finite element method, the effects of geometric architecture and polarization directions on the electromechanical properties including Poisson's ratios, elastic coefficients, piezoelectric stress coefficients, dielectric coefficients, and figures of merit in the auxetic piezoelectric ceramics are investigated in detail. Furthermore, the stress fields in conventional and proposed porous piezoelectric ceramics subjected to mechanical and electrical loads are compared and discussed. Finally, it can be concluded that the auxetic piezoelectric ceramic exhibits (a) giant negative Poisson's ratios (smaller than ), (b) negative elastic coefficients, (c) more extensible, higher piezoelectric sensitivity, lower acoustic impedance, stronger crack resistance than conventional porous piezoelectric ceramics with the same porosity, and (d) larger stiffness than conventional porous piezoelectric ceramics with similar figures of merit.

Relaxation processes in sodium–lithium niobate porous ceramics

In our work, we obtained and studied the samples of porous piezoelectric ceramics based on lithium – sodium niobate (LNN) with a pore content of 10, 20, 30, and 40 volume percent. An analysis of the structure, temperature and frequency dependences of the permittivity of the samples was carried out. It was shown that in all samples there are two main relaxation processes: in the regions of high (1 − 7 MHz) and low (10 Hz − 1 MHz) frequencies. The frequency at which a change in the type of dispersion occurs depends on the pores concentration in the sample.

Influence of porous configuration on dielectric and piezoelectric properties of KNN–BKT lead-free ceramic

Porous piezoelectric ceramics are the far and wide known graded functional materials. Of late, lead-free porous piezoelectric systems have increased enormous consideration, because of the factors inclusive of environmental friendly, light weight, low acoustic impedance and versatility. Porous lead-free (1-x) (K, Na) NbO3. x (Bi, K) TiO3 (KNN–BKT) solid solution, was synthesized by solid state method. The porogen utilized as part of this work was ammonium oxalate monohydrate in 10, 20, 30 and 40 wt% to get diverse porosity levels in the lead-free specimen. Primary evaluation of the porous specimen has been done with respect to its phase by XRD and surface microstructure using SEM. The specimens were poled and their piezoelectric coefficients were assessed at varied temperatures. Dielectric properties as a function of temperature and frequency are also reported for the specimens.

A Concise Review Encircling Lead Free Porous Piezoelectric Ceramics

A Concise Review Encircling Lead Free Porous Piezoelectric Ceramics

Experimental study of high intensity focused ultrasonic fields generated by piezocomposite transducers

In this paper, acoustic fields of HIFU transducers were studied experimentally. HIFU transducers based on focusing elements made from porous piezoelectric ceramics were fabricated and studied. The influence of HIFU transducers design features on acoustic fields generated in water were measured using 3D ultrasonic measurement systems UMS3 and calibrated hydrophones (Precision Acoustics Ltd.). Experimental results were compared with the FEM modeling of the forms of natural oscillations of the porous piezoelements on electric resonant and antiresonant frequencies. It was shown, that any kind of irregularities in the shape and size of focused piezoceramic element, working frequency, as well as transducers design peculiarities (housing, membrane etc.) strongly influence acoustic field distribution (acoustic pressure, side lobs level etc.). Ex vivo experiments on tissues and acoustic phantoms confirmed the results of measurements and calculations.