Porous Ferroelectric Ceramics Research Articles

Retrievable Hierarchically Porous Ferroelectric Ceramics for “Greening” the Piezo‐Catalysis Process

AbstractPowder‐based piezo‐catalysis, as an effective approach to degrade wastewater and produce hydrogen from water splitting, has been widely used in the field of energy conservation and pollution reduction. However, these hard‐to‐recycle powders pose a challenge of secondary pollution in the environment. As a result, this paper provides an alternative strategy based on the manufacture of porous ceramics as a green chemistry approach to replace ferroelectric powders currently used in traditional piezo‐catalysis. The piezo‐catalytic properties of Ba0.75Sr0.25TiO3 (BST) ceramics prepared using freeze casting and direct ink writing techniques are investigated in detail. The positive effect of introducing micro‐ and macro‐pores is explored and discovered, where a BST ceramic with hierarchical pore channels is prepared by a combination of direct ink writing and freeze casting and exhibts the highest first‐order kinetic rate constant per mass of catalysts, k, of up to 2.91 min−1 kg−1 compared to bulk BST ceramics. This study therefore provides the first report for the benefits of hierarchical porous ferroelectric ceramics used in water splitting, with an average H2 production rate reaching 848.88 nmol g−1 h−1.

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.

How to Make Porous Piezoelectrics? Review on Processing Strategies.

Ferroelectric ceramics are a technologically important class of materials that are currently exploited in actuators, sensors, transducers, and memory devices. The introduction of porosity into these materials has been proved to be an effective tool for tuning functional properties for specific applications, such as piezoelectric and pyroelectric devices and energy harvesters. In this review, a comprehensive description of the most widely used processing techniques able to produce porous ferroelectric ceramics is reported. In particular, the state-of-the-art production strategies including replica technique, direct foaming, sacrificial template method, and additive manufacturing used up to now for the realization of porous piezoelectric lead zirconate titanate (PZT)-based structures are critically reviewed and rationalized. Moreover, this work aims to give concrete indications on the more effective and actual production strategies that should be exploited for the development of porous PZT-based materials for the specific applications. Finally, two case studies are reported to remark the critical importance of material-processing-microstructure correlations on the functional properties of the designed devices.

High piezoelectric sensitivity and hydrostatic figures of merit in unidirectional porous ferroelectric ceramics fabricated by freeze casting

High performance lead zirconate titanate (PZT) ceramics with aligned porosity for sensing applications were fabricated by an ice-templating method. To demonstrate the enhanced properties of these materials and their potential for sensor and hydrophone applications, the piezoelectric voltage constants (g33 and g31), hydrostatic parameters (dh, gh, −d33/d31, dh·gh and dh·gh/tanδ) and AC conductivity as a function of the porosity in directions both parallel and perpendicular to the freezing temperature gradient were studied. As the porosity level was increased, PZT poled parallel to the freezing direction exhibited the highest dh, −d33/d31 and figures of merit dh·gh, dh·gh/tanδ compared to the dense and PZT poled perpendicular to the freezing direction. The gh, g33 and g31 coefficients were highest for the PZT poled perpendicular to the freezing direction; the gh was 150%–850% times higher than dense PZT, and was attributed to the high piezoelectric activity and reduced permittivity in this orientation. This work demonstrates that piezoelectric ceramics produced with aligned pores by freeze casting are a promising candidate for a range of sensor applications and the polarisation orientation relative to the freezing direction can be used to tailor the microstructure and optimise sensitivity for sensor and hydrostatic transducer applications.

Polarization-switching dynamics in bulk ferroelectrics with isometric and oriented anisometric pores

Highly porous ferroelectric ceramics possess remarkably less polarizability than dense ceramics; instead they display high tunability of various physical properties. Particularly, the shape and orientation of pores as well as the total porosity exhibit a great effect on the polarization-switching dynamics. In the present work, finite-element simulations of the electric-field distributions and related statistical distributions of local switching times are analysed and compared with the switching characteristics of porous lead zirconate titanate ceramics, extracted from the experiment by means of the inhomogeneous field mechanism model of polarization switching. Surprisingly, the simulated statistical field-distributions turn out to be virtually independent of the pore-size distribution; however, they are sensitive to the anisometric shape and orientation of the pores. Additionally, they exhibit notable broadening with increasing porosity; an effect confirmed by experimental observations.

Porous ferroelectrics for energy harvesting applications

This paper provides an overview of energy harvesting using ferroelectric materials, with a particular focus on the energy harvesting capabilities of porous ferroelectric ceramics for both piezo- and pyroelectric harvesting. The benefits of introducing porosity into ferro- electrics such as lead zirconate titanate (PZT) has been known for over 30 years, but the potential advantages for energy harvesting from both ambient vibrations and temperature fluctuations have not been studied in depth. The article briefly discusses piezoelectric and pyro- electric energy harvesting, before evaluating the potential benefits of porous materials for increasing energy harvesting figures of merits and electromechanical/electrothermal coupling factors. Established processing routes are evaluated in terms of the final porous structure and the resulting effects on the electrical, thermal and mechanical properties.

Phase Transition Experimental and Theoretical Study of Micro Power Generator Supplying Source for CMOS Chip Based on Ferroelectric Ceramic Nano-Porous Material.

We demonstrated both experimentally and in theory analysis and calculation that the tin-modified lead zirconate titanate nanoporous ferroelectric generator system can perform as a micro-power supplying source for CMOS chip. The ferroelectric ceramic phase transition under transverse shock wave compression can charge external storage capacitor. The nanoporous microstructure ferro-electric ceramic micro-pulsed-power system is capable of generating low output voltage pulses and supplying CMOS chip with micro power sources. We developed the methodology for theory analysis and experimental operation of the ferroelectric generator. Analysis of the porous ferroelectric ceramic material was carried out by X-ray diffractometry and X-ray photoelectron spectroscopy. Microstructures and surface morphology of porous ferroelectric ceramics samples were examined by using scanning electron microscopy. The planar shock wave experiments were conducted on a compressed-gas gun. The experimental results were in good agreement with the theory analysis. Keywords: PSZT Ferroelectric Ceramic, Shock Wave, Phase Transition, Depolarization, Micro-Power-Generator.

Piezoelectric Response from Porous Ferroelectric Ceramics at Low Drive Voltage

The piezoelectric response (PR) images of unpolarized piezoceramics PCR-1 were obtained under weak effect of the probe on the surface. The frequency dependence of PR amplitude in the range of 4–50 kHz was measured. PR creates stripes, which amplitude and size vary smoothly with frequency. The main maximum of PR amplitude (12-15 kHz) differs for crystallite and grain boundary. The decoupled approximation in the PR theory of ferroelectric-semiconductor and wave processes in a piezoelectric plate under applied alternating electric field were used to discuss a possible origin of the stripes in PR images and PR amplitude change with frequency.

Breakdown and critical field evaluation for porous PZT 95/5 ferroelectric ceramics under shock wave compression

Bounded charges of PZT 95/5 ferroelectric ceramics with polarization can be rapidly released by shock wave loadings to form a high-power electrical energy output, which motivates pulsed power applications of ferroelectric materials. In the present paper, we first investigated experimentally the depoling current and output electric field, as well as the critical electric fields of breakdown for porous PZT 95/5 ceramics in the normal shock-wave-loaded mode by means of a gas-gun facility. By combining the output electric-field profile by shock loading with the breakdown of the quasi-static electric field, we were able to theoretically evaluate the range of the breakdown field for porous ferroelectric ceramics with different porosities under shock wave compression. Although it is a rough bound-field evaluation on breakdown of shocked porous PZT 95/5 ferroelectric ceramics suggested in the present work, it sounds reasonable and the predictions of critical field-bounds on the breakdown show good agreement with the magnitude of the experimental results. The influences of load resistance, porosity and velocity of shock wave on the lower and upper bounds of critical electric field for poled porous PZT 95/5 ceramics during the discharge process were also discussed.

Porous Ferroelectric Ceramic as Gas Sensor Based on BaTiO3/SiO2

The present work aims to develop a gas sensor based on porous ferroelectric ceramics prepared with BaTiO3 and SiO2 which pore size and percentage of porosity were controlled. The sensors were prepared by the mixed oxide route. The characterization showed that an increment on SiO2 in the mixture produces an increment in pore size and percentage of porosity. The permittivity-temperature curve was also analyzed. When a gas flows across the pores, the air caught in the pores, is displaced. This process produces measurable permittivity changes. The relationship between sensitivity of sensor and its percentage of porosity were registered. The fabricated ceramics exhibited different sensitivities (permittivity changes) to: helium flow, oxygen flow, carbon dioxide and cigarette smoke.

Structural Evolving Sequence and Porous Ba6Zr2Nb8O30 Ferroelectric Ceramics with Ultrahigh Breakdown Field and Zero Strain

Microstructural evolving sequence of relaxor ferroelectric Ba6Zr2Nb8O30 (BZN) ceramics has been investigated and discussed. Porous BZN, which has an irregular grain network with pores, can be obtained within a narrow sintering window (sintering temperature of ~1250°C and dwelling time of ~5 h in our experiments). X‐ray diffraction‐based structure refinements determine the atomic positions and confirm that the porous ceramics has tetragonal tungsten bronze structure with P4bm space group symmetry. It is found that the most porous ceramic has the lowest dielectric constant, highest electric field breakdown strength, and nearly zero macroscopic electric field‐induced strain. These features can be related to the porous microstructures by comparing with the denser counterparts and can be well understood by using brick‐wall model. Our results may provide useful information for the understanding of microstructure evolving sequence of BZN during sintering and the structural effects on electric properties of ceramics. Our work may also provide a reliable way for developing porous ferroelectric ceramics with special properties.

Measurements of the thermal, dielectric, piezoelectric, pyroelectric and elastic properties of porous PZT samples

The introduction of porosity into ferroelectric ceramics has been of great interest in recent years. In particular, studies of porous lead-zirconate-titanate ceramic (PZT) have been made. In the research reported, samples of Ferroperm Pz27 with porosities of 20, 25 and 30% were studied. Very complete measurements were made of all of the physical properties relevant for ferroelectric applications including thermal conductivity and diffusivity, heat capacity, dielectric, pyroelectric, piezoelectric and elastic properties. Scanning electron micrographs indicated a change from 3-0 to 3-3 connectivity with increasing porosity. Although most of the physical properties are degraded by the presence of porosity, both piezoelectric and pyroelectric flgures-of-merit are improved because of the markedly reduced relative permittivity. Porous ferroelectric ceramics are very promising materials for a number of applications.

Microstructural modelling of the polarization and properties of porous ferroelectrics

Micromechanical models of porous ferroelectric ceramics have often assumed that thematerial is fully polarized in a particular direction and/or consists of a single isolated pore.In this work the polarization state in three-dimensional porous polycrystalline ferroelectricnetworks has been modelled to eradicate the oversimplification of these idealized unit cells.This work reveals that microstructural network models more closely represent a porousferroelectric microstructure since they are able to take into account the complexpolarization distribution in the material due to the presence of high and low permittivityregions. The modelling approach enables the prediction of the distribution ofpoled and unpoled material within the structure. The hydrostatic figures of meritand permittivity were determined for a variety of porous lead zirconate titanatemicrostructures and found to be in good agreement with experimental data. The decreasein piezoelectric activity with porosity was observed to be associated with thecomplex polarization state within the material. Model results were shown to bemuch improved when compared to a model assuming a fully polarized model.

Permeability Behavior of Porous Piezoelectric Ceramics Prepared in Layers in Response at AC Voltage on Electrode Implanted

Porous ferroelectric layered ceramics were prepared by the use of quartz and barium titanate and implanted during their fabrication with a nickel chrome wire which served as an internal electrode. The permeability coefficient was determined by the method of fine land, the law of Darcy and supplying an alternating current stimulus with different frequencies to the wire implant. Permeability tests present a direct relationship between the frequency applied and the permeability coefficient responses.

Analysis of switching properties of porous ferroelectric ceramics by means of first-order reversal curve diagrams

Particular aspects of the switching properties of the Nb-PZT ceramics with anisotropic porosity (40% relative porosity) were investigated by comparison with the dense ceramics (5% relative porosity) of the same composition by means of the first-order reversal curve (FORC) analysis. The reversible/irreversible components give different contributions to the total polarization: A sharp FORC distribution with an almost negligible reversible component is characteristic to the dense material, while a broad distribution with an important reversible component is characteristic for the porous one. The coercivity corresponding to the maximum of the irreversible component is the same irrespective to the sample density and pore's configuration with respect to the electrodes: ${E}_{c,M}=1.5\phantom{\rule{0.3em}{0ex}}\mathrm{kV}∕\mathrm{mm}$, while the bias fields are zero for the dense ceramic, small and positive; ${E}_{\text{bias},M}=50\phantom{\rule{0.3em}{0ex}}\mathrm{V}∕\mathrm{mm}$, when the major axis of the elongated pores is parallel with the electrodes and negative; ${E}_{\text{bias},M}=\ensuremath{-}100\phantom{\rule{0.3em}{0ex}}\mathrm{V}∕\mathrm{mm}$, when this axis is perpendicular to the electrodes. The influence of the dipolar coupling leading to such bias fields is explained by considering that the particular microstructure is causing a symmetry breaking, decoupling the dipolar interaction (forward or laterally). A dipolar (discrete) model with random orientations of the dipoles' directions was used to simulate this confinement effect. The calculated FORC diagrams lead to the same type of bias as the experimental ones, proving that the lateral confinement gives an intrinsic contribution to the biased $P(E)$ loops observed for the porous ceramics. In addition with other possible extrinsic contributions, this dipolar coupling can be a source of the built-in field in confined ferroelectric structures. The experimental FORC distribution was used as input in a Preisach-type model to recompose the major and symmetric minor hysteresis loops and a remarkable agreement with the experimental data was obtained. The FORC method proves to be an excellent tool in describing the ferroelectric systems, simulating polarization experiments, and predicting outputs of the circuits with ferroelectric capacitors. In the particular case of the porous anisotropic ceramics, the combined experimental and analytical FORC analysis allowed us to probe and to describe qualitatively the presence of the bias field as a result of the geometrical confinement.

Prediction of the properties of two-phase composites with a piezoactive component

The effective dielectric, piezoelectric, and elastic constants of two-phase macroscopically piezoactive 3-0 and 3-3 composites are calculated. It is assumed that one of the components is a polarized ferroelectric ceramic material and the other is an inactive material with variable elastic properties. The limiting case when the elastic compliances of the inactive material tend to infinity (porous ferroelectric ceramics) is considered. The adequacy of this model to production technologies of piezoelectric composites is discussed. Computational results are compared with experimental data.

Lead Titanate and Lead Metaniobate Porous Ferroelectric Ceramics

A manufacturing technology of porous ferroelectric ceramics on the base of pure and modified lead titanate and lead metaniobate compositions were developed. Special attention was given to the microstructure studying of porous ceramics with different porosity types. The porosity dependencies of elastic, dielectric and piezoelectric properties of the specified compositions were measured in 0–40% relative porosity range. It was shown that, the porous ceramics technology allows to produce stable in time piezoelements of such “technologically difficult” ceramics as lead titanate and lead metaniobate with excellent and reproducible properties.

BTS: A new ferroelectric for multifunctional sensors

Abstract A new series of multifunctional sensitive ferroelectric ceramics, BaTiO3-BaSnO3 have been studied. They can rapidly detect temperature, humidity and gas presence by means of a single sensor. This is the first time that such multifunctional sensors have been reported. The crystalline phase, porous structure, pore system, semiconduction and temperature-humidity-gas sensing characteristics of BTS porous ferroelectric ceramics were investigated.