Porous Piezoceramics Research Articles

Influence of Pore Shape and Initial Stress State on the Electroelastic Properties of Porous Piezoceramics PZT-4

Influence of Pore Shape and Initial Stress State on the Electroelastic Properties of Porous Piezoceramics PZT-4

Switching Processes and Ferroelectric Hysteresis in Dense and Porous Piezoceramics in the Lead Zirconate Titanate System

Switching Processes and Ferroelectric Hysteresis in Dense and Porous Piezoceramics in the Lead Zirconate Titanate System

Complex Electromechanical Parameters and Features of the Microstructure of Porous Piezoceramics of the Lead Zirconate Titanate System

Complex Electromechanical Parameters and Features of the Microstructure of Porous Piezoceramics of the Lead Zirconate Titanate System

Complex electromechanical parameters and microstructure peculiarities of PZT-type porous piezoceramics

In this work, we studied the microstructure peculiarities and complex electromechanical parameters of porous piezoelectric ceramics based on the PZT system with different relative porosity and pore sizes. The complex elastic, dielectric, and electromechanical parameters of the porous piezoceramics were measured on the radial vibrational mode of standard samples and analyzed using piezoelectric resonance analysis (PRAP) software. It was revealed that the microstructural features of porous piezoceramics defined the character of the porosity dependences of real and imaginary parts of dielectric, piezoelectric, and electromechanical properties of porous piezoelectric ceramics.

Electromechanical and ferroelectric hysteresis in dense and porous PZT-type piezoceramics

In the present study, particular aspects of the large-signal switching properties and electromechanical hysteresis of the lead zirconate titanate (PZT)-type porous piezoceramics were studied in comparison with the dense piezoceramics of the same composition. Large-signal ferroelectric polarization and strain hysteresis loops were recorded at the bipolar electric fields in the range of 0 ÷ 5 kV/mm and in the frequency range of 0.01 ÷ 5 Hz. Measurements and analysis were performed by means of the electromechanical measurement system (STEPHV) and electromechanical response characterization program (STEP), combining large-signal modeling of the mechanical and electrical behavior of ferroelectric materials.

Influence of Pore Shape and Initial Stress State on the Electroelastic Properties of Porous Piezoceramics PZT-4

Influence of Pore Shape and Initial Stress State on the Electroelastic Properties of Porous Piezoceramics PZT-4

MODELING OF VIBRATIONS OF A STACKED PIEZO ELEMENT MADE OF POROUS PIEZOCERAMICS

The work is devoted to a numerical study of the effectiveness of using porous piezoceramics in a stacked piezoelectric element, which can be used as a power drive element, a piezoelectric generator, or an ultrasonic emitter. The use of porous piezoceramics in stacked piezoelements has not received enough attention in the literature. The use of porous piezoceramics in stacked piezo elements has not received enough attention in the literature. The paper considers a stacked piezo element consisting of eight solid cylinders counter-polarized in the axial direction. The material of the cylinders is PZT-4 piezoceramic, the porosity of which varies from 0% to 80%. The problem of axial steady-state oscillations in the vicinity of the first resonance frequency and below it is solved. The lower end of the cylinder is fixed along the normal, excitation of oscillations is carried out by mechanical action under uniformly distributed pressure at the upper face or by the action of electric potential difference at the electrodes. The problems are solved in the framework of linear axisymmetric theory of electroelasticity. With mechanical action, the output characteristic of the device is the electrical potential of the free electrodes; with electrical action, it is the amplitude of the axial vibrations of the upper end or the reaction force if it is fixed. The finite element method implemented in the ACELAN package is used as the solution method. As a result of the numerical solution, the dependence of the percentage of porosity on the output characteristics of the piezo element is investigated: the frequencies of resonance and antiresonance, the electromechanical coupling coefficient, the output potential under mechanical loading, the amplitude of oscillations of the free upper end and the coupling reaction at its fixing when the oscillations are excited by the potential difference and the energy of the elastic element attached to this end. The analysis of the dependence of these characteristics allows us to conclude that it is reasonable to use such an element with porous ceramics as a piezoelectric generator and transmitter. It is noted that the choice of the percentage of porosity depends directly on the intensity of loads and the strength of porous piezoceramics.

Exploring the Mpemba effect: a universal ice pressing enables porous ceramics.

Piezoceramics with global porosity and local compaction are highly desired to exploit the combination of mechanical and electrical properties. However, achieving such a functional combination is challenging because of the lack of techniques for applying uniform pressure inside porous ceramic green parts. Nature provides many examples of generating strong forces inside the macro and micro channels via the state transformation of water. Inspired by these phenomena, we present a technique of "ice and fire", that is, water freezing (ice pressing) and high-temperature sintering (fire), to produce ideal porous piezoceramics. We introduce a new compaction method called the "ice pressing method", which manipulates liquid phase transition for compaction. This method has several advantages, including uniform pressure distribution, a wide pressure range, high effectiveness, and selective freezing. It can generate an ultrahigh pressure of up to 180 MPa on the piezoceramic green skeletons in minutes while retaining their functional pore structures. By exploiting the Mpemba phenomenon, we further accelerate the compaction procedure by 11%. The first ice-pressed and second fire-consolidated lead zirconate titanate (PZT) ceramics are highly densified and exhibit an outstanding piezoelectric response (d33 = 531 pC N-1), comparable to conventional pressed bulk counterparts and 10-20 times higher than those of unpressed materials. The novel ice pressing method breaks the limitation of lacking a compaction technique for porous ceramics. The versatile and effective ice pressing method is a green and low-cost route promoting applications in sensors, acoustics, water filtration, catalyst substrates, and energy harvesting.

Computer homogenization of porous piezoceramics of different ferrohardness with random porous structure and inhomogeneous polarization field

The article is concerned with the homogenization problems, in which the effective moduli of porous piezoceramic composites are determined taking into account the inhomogeneity of the polarization field. The homogenization problems are solved by the finite element method in the framework of the theory of effective moduli and the Hill energy principle using the ANSYS package. To this end, in static problems of electroelasticity, the displacements and electric potential, which are linear in spatial variables, are specified on the boundary of a representative volume to provide constant stress and electric induction fields for a homogeneous reference medium. After solving a set of boundary value problems under different boundary conditions and determining the volume-averaged stress components and the electric induction vector, a complete set of effective moduli for the piezoelectric composite is calculated. A representative volume of the piezocomposite is created in the form of a regular finite element mesh consisting of cubic elements. Pores in the representative volume are assumed to be filled with a piezoelectric material with extremely small moduli. Finite elements with pore properties are selected according to a simple random algorithm. The inhomogeneous polarization field is found by solving an electrostatic problem, in which the polarization process in the representative volume is modeled based on a simplified linear formulation. The local coordinate systems for individual finite elements of the composite matrix are specified by the directions of the polarization vectors. In the following, when solving the problems of electroelasticity, these local coordinate systems associated with the elements of the piezoelectric matrix allow recalculating the material properties according to the formulas of transformation of the tensor components as the coordinate systems rotate. In addition, consideration is given to different models describing the change in the moduli of the material from an unpolarized state to a polarized one as a function of the polarization vector. Computational experiments were carried out for three types of piezoceramics: soft ferroelectric piezoceramics PZT-5H, piezoceramics PZT-4 of medium ferrohardness, and piezoceramics PZT-8 with higher degree of ferrohardness. The dependences of the effective moduli on porosity are compared for different laws of polarization inhomogeneity and different kinds of piezoceramic material of the composite matrix.

Multilayer digital materials based on porous piezoceramics and polymer matrix with the inclusion of conductive components

A digital material in the form of a composite consisting of particles of porous ferroelectric ceramics and a polymer matrix with the inclusion of metal particles was obtained. The properties of this material, as well as the properties of the polymer-metal matrix, were investigated. It is shown that this matrix has a high local conductivity. This provides electrical contact between the particles of porous piezoceramics, which is the main factor that ensures the presence of piezoelectric properties in this composite.

Construction of Flexible Piezoceramic Array with Ultrahigh Piezoelectricity via a Hierarchical Design Strategy

AbstractThe µW‐level power density of flexible piezoelectric energy harvesters (FPEHs) restricts their potential in applications related to high‐power multifunctional wearable devices. To overcome this challenge, a hierarchical design strategy is proposed by forming porous piezoceramics with an optimum microstructure into an ordered macroscopic array structure to enable the construction of high performance FPEHs. The porous piezoceramic elements allows optimization of the sensing and harvesting Figure of merit, and the array structure causes a high level of effective strain under a mechanical load. The introduction of a network of polymer channels between the piezoceramic array also provides increased device flexibility, thereby allowing the device to attach and conform to the curved contours of the human body. The unique hierarchical piezoceramic array architecture exhibits superior flexibility, a high open circuit voltage (618 V), high short circuit current (188 µA), and ultrahigh power density (19.1 mW cm−2). This energy density value surpasses previously reported high‐performance FPEHs. The ultrahigh power flexible harvesting can charge a 0.1 F supercapacitor at 2.5 Hz to power high‐power electronic devices. Finally, the FPEH is employed in two novel applications related to fracture healing monitoring and self‐powered wireless position tracking in extreme environments.

ЭЛЕКТРОУПРУГИЕ СВОЙСТВА НАЧАЛЬНО-НАПРЯЖЕННОЙ ПЬЕЗОКЕРАМИКИ PZT-4 С ОДНОНАПРАВЛЕННЫМИ ТУННЕЛЬНЫМИ ПОРАМИ

Prediction results and numerical analysis of effect on effective transversal-isotropic electroelastic properties of porous piezoceramics of PZT-4 with unidirectional cylindrical (tunnel) pores of values of its initial axisymmetric stress state are presented. Effective constants have been identified: Young's and shear modules, Poisson's ratio in the transversal plane of isotropy and the "longitudinally/transverse" piezomodule of porous ceramics, which are most significantly influenced by the nature and values of its initial deformation in comparison with other practically "invariant" constants. It has been found that the "transversal" hydrostatic initial deformation of the porous ceramic has a greater effect on the effective constants of the porous ceramic than the same values of the "longitudinal" axial initial deformation.

FINITE ELEMENT CALCULATION OF DISK TRANSDUCER WITH CYMBAL-SHAPED END-CAPS AND ACTIVE ELEMENT FROM POROUS PIEZOCERAMICS WITH EXTREME CONDUCTIVITY OF PORE SURFACES

The paper presents a finite element analysis of a disk-shaped piezoelectric transducer with end-cap patches, which is usually called as Cymbal transducer. The efficiency of such a transducer is determined both by its geometric dimensions and by the values of the longitudinal and transverse piezoelectric moduli (piezoelectric charge coefficients) of the piezoceramic disc material. As was recently found, for porous piezoceramics with completely metallized pore surfaces, the effective transverse piezoelectric modulus does not decrease in absolute value with increasing porosity, as in conventional porous piezoceramics, but, on the contrary, increases, as does the longitudinal piezoelectric modulus. These unusual properties of porous piezoceramics with pore surface metallization are determined by the extreme properties of the phases that make up the piezocomposite material, and, in particular, the extremely high conductivity of the pore surface material inside the dielectric composite medium. In this regard, the main task was to study the efficiency of the Cymbal transducer depending on the type of porous piezoelectric disc material. Comparisons were made for solid piezoceramics, for ordinary porous piezoceramics, for porous piezoceramics with a very thin metal coating of the pores, and for porous piezoceramics with a relatively thick metallization layer on the surface of the pores with different porosities. In the ANSYS finite element package, steady-state oscillations of the cymbal transducer were calculated under nonresonant operating modes and near the first electrically active frequencies, which corresponds to the use of the transducer as a device for energy harvester and as a piezoelectric emitter of acoustic waves. In both cases, the results of computational experiments showed the promise of using new types of porous piezoceramic materials for the considered configurations of a disk piezoelectric transducer with end-cap cymbal patches. In this case, the best results were obtained for a porous piezoceramic material with a very thin metal coating of the pores.

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.

Structural features and electrophysical properties of the “piezoceramic-polymer” composites

Composites of a mixed type, consisting of porous piezoceramics particles in a polymer matrix, were produced and studied. A fabrication technique of such composites with 0–3 and 1–3 connectivities suitable for 3D printing method was presented. Their dielectric, electromechanical, and piezoelectric characteristics were measured. Dependences of dielectric permittivity on the number of layers of piezoceramic particles in the composite sample and on the ratio between the particle size and piezoelement thickness were presented. Single layer composites with appropriate ratio of the sample thickness and piezoelectric particles diameter demonstrated piezoelectric and electromechanical properties close to those of the initial piezomaterials.

Additive manufacturing of lead-free KNN by binder jetting

Additive manufacturing of lead-free piezoceramics is of great interest, given the large request of application-oriented designs with optimal performances and reduced material consumption. Binder Jetting (BJ) is an additive manufacturing technique potentially suited to the production of ceramic components, however the number of feasibility studies on BJ of piezoceramics is extremely limited and totally lacking in the case of sodium-potassium niobate (KNN). In this work, as-synthesised powders are employed in the BJ 3D printing process. Microstructural properties, such as porosity, grain size distributions, and phase composition are studied by SEM, XRD and MIP (Mercury Intrusion Porosimetry) and compared to die-pressed pellets. Analyses reveal considerable residual porosity (~40%) regardless of the printing parameters, with a weak preferential orientation parallel to the printing plane. The piezoelectric characterization demonstrates an outstanding d33 value of 80–90 pC N−1. Finally, Figures of Merits for the employment as porous piezoceramics in the direct mode are presented.

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.

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.

Elastic losses and dispersion in porous piezoceramics

In this work, complex studies of the elastic dispersion and losses in porous piezoceramics based on solid solutions of the PZT system were carried out. Full set of complex constants of porous ceramics with different porosity and their frequency dependences were measured using the piezoelectric resonance analysis method.The microstructural and physical mechanisms of elastic losses and dispersion in porous piezoceramics were considered.