Porous Porous Lead Zirconate Titanate Ceramics Research Articles

Tailoring the Microstructure and Porosity of Porous Piezoelectric Ceramics for Ultrasonic Transducer Application.

Porous piezoelectric ceramics and composites are advantageous for ultrasonic transducers due to their capability to decouple longitudinal and transverse modes, their improved voltage sensitivity, and their enhanced acoustic matching. However, the design and fabrication of porous piezoelectric ultrasonic transducers with excellent electromechanical properties are still challenging. In this work, porous lead zirconate titanate (PZT) ceramics with an aligned pore structure were prepared using the freeze-cast technique, and the effect of porous structure and porosity on the electromechanical parameters was investigated. The introduction of an aligned pore structure is beneficial to enhance the electromechanical properties and reduce the acoustic impedance. A high d33 (∼530 pC/N), a higher kt (∼0.676), and a lower acoustic impedance (∼10.4 MRalys) were achieved in the porous PZT ceramic with the porosity of 44 vol %. The effect of porosity and pore structure on the decoupling degree of vibration modes and ferroelectric polarization was considered to correct the homogeneous medium model, which can quantify the relationship between the kt and porosity of the porous structure. A demonstration of a piezoelectric ultrasonic transducer based on freeze-cast porous PZT ceramics was presented, which exhibits a -6 dB bandwidth of 52% and a theoretical axial resolution of 520 μm. This work therefore provides a potential alternative of piezoelectric ultrasonic transducers for nondestructive testing and imaging applications.

Fabrication and properties of 3-3 type PZT-ordinary Portland cement composites

In this study, porous lead zirconate titanate (PZT) ceramics with porosity ranging from 46.4% to 82.3% were produced by the gel casting technology of particle-stabilized ceramic foams with the solid loading of 5–25 vol%, then the Portland cement paste was cast in porous PZT ceramics with continuous vibration to fabricate 3-3 type cement-based piezoelectric composites. The microstructure, dielectric, piezoelectric, and electromechanical coupling properties of the composites were characterized. With the increase in initial solid loading of PZT slurry, both the porosity, open porosity and pore size of porous PZT ceramics decreased correspondingly, which have prevented the filling of cement paste into the porous ceramics and led to the increment of PZT content in the composites. Increase in the PZT content contributed to the relative permittivity (εr) and longitudinal piezoelectric strain coefficient (d33), and a resultant reduction in piezoelectric voltage coefficient (g33). The prepared composites possessed a maximal thickness electromechanical coupling coefficient (Kt) value of 41.22%, higher than that of planar electromechanical coupling coefficient (Kp), indicating enhanced thickness mode oscillations of the composite. With the increase in PZT volume fraction, the PZT-cement composites turned from typical 3-3 structure to appoximate sandwich structure gradually, leading to more energy loss during electromechanical process and obvious decrease of the mechanical quality factor (Qm). The acoustic impedance (Z) of specimens ranged from 6.69 to 8.27 MRayls, close to that of cement materials (∼10 MRayls), making them promising candidate for application in civil engineering.

Fabrication of porous PZT ceramics using micro-stereolithography technology

Based on micro-stereolithography (μSL) additive manufacturing (AM) followed by the use of the burnable plastic sphere (BURPS) technique, we present the fabrication of porous lead zirconate titanate (PZT) ceramics. A printing slurry was prepared by mixing photocurable ceramic suspensions with various contents of polymethylmethacrylate (PMMA) as a pore-forming agent (PFA). We found that the cure depth increased gradually with increasing PMMA content. The sintered PZT ceramics exhibited a porous microstructure of predominantly spherical pores formed by PMMA, with sizes ranging from ~15 to 35 μm. The porosity of the PZT ceramics increased from 11.3% to 21.9%, corresponding to a decrease in the density from 6.92 to 6.09 g/cm3 due to the increasing PMMA content. As the porosity increased, the acoustic impedance decreased from 24.4 to 12.6 MRayls (106 kg/m2 s). The porous PZT ceramic with 5 wt% PMMA exhibited superior dielectric and piezoelectric properties (d33 = 525 pC/N, εr = 2417, tanδ = 0.04) that were comparable to those of ceramics fabricated by conventional methods. These results suggest that μSL technology is a viable alternative for fabricating porous PZT ceramic components, especially pieces with complex geometric structures.

Piezoelectric and mechanical properties of CaO reinforced porous PZT ceramics with one-dimensional pore channels

The formation of capillaries in sodium alginate gels is a dissipative process driven by unidirectional diffusion of divalent cations into sodium alginate sols. In the present work, we have prepared 3-1 type porous lead zirconate titanate (PZT) ceramics with oxides (CaO) being doped on a molecular level from the dissipative process by incorporating PZT particles into the sodium alginate gel matrix. By varying the concentration of cation solutions (CaCl2) from 0.5mol/L to 2.5mol/L, both the microstructure, doping amount of oxides (CaO) and crystalline phase of the porous PZT ceramics were tailored. Accordingly, increase in the concentration of Ca2+ has led to a reduction in the relative permittivity (εr) first, and then an increase, while the piezoelectric coefficient (d33 and d31) demonstrated an opposite variation tendency. The prepared samples possessed a maximal HFOM value of 4755×10–15Pa−1 when the concentration of Ca2+ was 1.0mol/L. Addition of CaO was found to improve the compressive strength of porous PZT ceramics, which was preferential to promoting the stability and reliability for application.

Control of pore size and wall thickness of 3-1 type porous PZT ceramics during freeze-casting process

3-1 type porous lead zirconate titanate (PZT) ceramics with unidirectionally aligned pore channels were prepared by freeze-casting process of which the freezing temperature was varied at −10~−100°C, and the solid content of slurries was changed at 15~40vol%. Characterization of pore size distributions and wall thickness distributions demonstrated the freezing temperature significantly influenced the pore size and wall thickness, while the solid content had strong influence on the porosity. When the solid content was stationary, the pore size decreased with decreasing freezing temperature and the wall thickness also tended to decrease. When the freezing temperature was constant, the porosity decreased as the initial solid content increased, meaning decreased ratio of pore size and wall thickness. The fabricated samples exhibited high piezoelectric coefficient and there was a trend that it increased with the simultaneous decrease of pore size and wall thickness.

Effects of sintering behavior on piezoelectric properties of porous PZT ceramics

Porous lead zirconate titanate (PZT) ceramics were fabricated by the gel-casting process of particle-stabilized wet foams and sintered at different temperatures. The bulk density and grain size of porous PZT ceramics increased with the increase of sintering temperature from 1150 to 1250 °C, which exerted remarkable influence on the value of relative permittivity (εr) and piezoelectric strain coefficient (d31 and d33). The relationship between microstructure and electric properties was explained by the space-charge theory reasonably. Under the joint effects of bulk density and grain size, the value of dh and gh decreased with the increase of sintering temperature, resulting in the decrease of hydrostatic figure of merit (HFOM) values from 12633 to 3427×10–15 Pa−1.

Effects of foam composition on the microstructure and piezoelectric properties of macroporous PZT ceramics from ultrastable particle-stabilized foams

Abstract Porous lead zirconate titanate (PZT) ceramics could be produced by combining the particle-stabilized foams and the gelcasting technique. In this study, the foaming capacity of particle-stabilized wet foams was tailored by changing the concentration of valeric acid and pH values of suspension. Accordingly, porous PZT ceramics with different porosity, microstructure, dielectric and piezoelectric properties were prepared with the respective wet foam. Increase in the porosity led to a reduction in the relative permittivity ( e r ), a moderate decline in the longitudinal piezoelectric strain coefficient ( d 33 ) and a rapid decline in the transverse piezoelectric strain coefficient ( d 31 ), which endowed porous PZT ceramics with a high value of hydrostatic strain coefficient ( d h ) and hydrostatic figure of merit (HFOM). As a result, the prepared samples possessed a maximal HFOM value of 19,520×10 −15 Pa −1 with the porosity of 76.3%. The acoustic impedance ( Z ) of specimens had the lowest value of 1.35 Mrayl, which could match well with those of water or biological tissue; accordingly, the material would be beneficial in underwater sonar detectors or medical ultrasonic imaging.

Piezoelectric Properties of the 1-3 Type Porous Lead Zirconate Titanate Ceramics

Porous lead zirconate titanate (PZT) ceramics are of great interest for hydrophones and medical imaging applications. The 0–3 type and 3–3 type porous PZT ceramics have been extensively discussed these years but the 1–3 type PZT ceramics have seldom been reported. This paper describes the fabrication process to obtain such 1–3 type porous PZT ceramics with one-dimensional pore channels by using tert-butyl alcohol-based directional freeze-casting method, and presents analysis of both microstructure and functional properties. The 1–3 type porous PZT ceramics with porosity ranging from 28.1% to 68.7% were fabricated by adjusting initial solid loading. With the increase of porosity, relative permittivity (ɛr) decreased slightly and longitude piezoelectric coefficient (d33) exhibited only a small decline, which could be attributed to the special 1–3 type porous structure. The resultant samples with 61.3% porosity possessed a high value of hydrostatic figure of merit, >100 times higher than that of dense materials. The acoustic impedance (Z) showed a linear dependence on porosity with the lowest magnitude reaching 1.3 MRayls (106 kg·(m2·s)−1), matching very well with biological tissue or water.

Porous PZT Ceramics with High Hydrostatic Figure of Merit and Low Acoustic Impedance by TBA‐Based Gel‐Casting Process

Porous lead zirconate titanate (PZT) ceramics with three‐dimensionally interconnected pores were prepared using a novel tert‐butyl alcohol‐based gel‐casting process, an unconventional technique in acquiring high‐porosity ceramics. In the present work, PZT ceramics with porosity ranging from 31.3% to 58.6% were fabricated by adjusting the initial solid loading and sintering temperature. The fabricated samples were characterized in terms of both porous structure and functional properties to clarify the underlying correlation. With the increase of porosity, relative permittivity (ɛr) decreased to a significantly low value compared with dense PZT ceramics while the longitude piezoelectric coefficient (d33) exhibited a moderate decline, which could be attributed to the unique structure with homogeneous pore distribution. As a result, the resultant samples possessed a high value of hydrostatic figure of merit, >100 times higher than that of dense materials. The acoustic impedance (Z) showed a linear dependence on porosity with the lowest magnitude reaching 3.0 MRayls (106 kg·(m2·s)–1), hopefully leading to enhanced coupling with biological tissue or water.

Effects of sintering behavior on microstructure and piezoelectric properties of porous PZT ceramics

Porous lead zirconate titanate (PZT) ceramics with interconnected pores were fabricated by using a novel tert-butyl alcohol (TBA)-based gel-casting method. The resultant samples were sintered at different temperatures and subsequently characterized in terms of both microstructure and piezoelectric properties to study effects of sintering behavior. Both microstructure and piezoelectric properties exhibited obvious dependence on sintering temperature. It was noted that porosity and grain size played dominant roles in determining the magnitudes of dielectric constant ( ɛ) and piezoelectric constant d 33, respectively. With the increase of sintering temperature, the porosity declined and the grain size increased which exerted opposite influences on piezoelectric properties mainly via ɛ and d 33. Since anti-interference ability of the ceramic correlates linearly with ɛ, it is possible to adjust sintering temperature to tailor porosity and pore morphology in order to achieve optimum piezoelectric properties as well as relatively high anti-interference ability.

Microstructure and electrical properties of porous PZT ceramics derived from different pore-forming agents

Porous piezoceramics have promising applications in underwater sonar detectors or medical ultrasonic imaging. We report the electrical and acoustic properties based on different pore microstructures of porous lead zirconate titanate (PZT) ceramics, fabricated using stearic acid (SA) and polymethylmethacrylate (PMMA) as pore-forming agents. The corresponding ferroelectric and piezoelectric properties decreased with increasing porosity due to the decrease in volume fraction of PZT phase, and were in good agreement with a modified cubes model in the case of isolated porosity. The corresponding acoustic impedance decreased from 16 to 8 MRayls (10 6 kg/m 2 s), with increasing porosity from 3% to 43%, due to low acoustic impedance of pore phase. The electrical properties of porous PZT ceramics were closely associated with porosity and the interconnection of pores, but only slightly associated with the shape of pores. However, the acoustic impedance was only connected to porosity, not to either shape or interconnection of pores.

The effects of sintering behavior on piezoelectric properties of porous PZT ceramics for hydrophone application

Porous lead zirconate titanate (PZT) ceramics were fabricated by adding polymethyl methacrylate (PMMA) and the effects of sintering behavior on their microstructure and piezoelectric properties were investigated. The porosity of PZT ceramics decreased with an increase in the sintering temperature at a fixed PMMA addition. The dielectric constant ( ɛ), longitudinal piezoelectric coefficient ( d 33) and hydrostatic figures of merit ( d h g h) of 34% porous PZT ceramics increased with an increase in sintering temperature from 1050 to 1300 °C. When sintered at 1300 °C, longitudinal piezoelectric coefficient of 34% porous PZT ceramic was very close to that of 95% dense PZT ceramics, while the hydrostatic figures of merit of 34% porous PZT ceramics is about fifteen times more than that of 95% dense PZT ceramics. Compared with PZT–polymer composites, the dielectric constant of 34% porous PZT sintered at 1300 °C is much higher, which can be more efficient to resist the interference in receiving sensitivities caused by loading effect of the cable.

Processing and piezoelectric properties of porous PZT ceramics

5–45% porous lead zirconate titanate (PZT) ceramics were fabricated by adding pore formers such as polymethyl methacrylate (PMMA) and dextrin and sintering at 1200 °C for 2 h. The optimum heating procedure was decided according to the thermogravimetric analysis of pore formers. The effects of different pore formers and their content on the microstructure and piezoelectric properties were investigated. With an increase in the content of pore formers, the porosity of sintered ceramics increased, which led to reduced dielectric constant ( ɛ 33) and longitudinal piezoelectric coefficient ( d 33) as well as enhanced hydrostatic piezoelectric voltage coefficient ( g h) and hydrostatic figures of merit ( d h g h). The hydrostatic figures of merit ( d h g h) of 41% porous PZT were 10 times more than that of 95% dense PZT.

Effects of porosity and grain sizes on the dielectric and piezoelectric properties of porous PZT ceramics and their mechanism

Porous lead zirconate titanate (PZT) ceramics were prepared by adding pore formers, and the effects of pore structure and grain sizes on the dielectric and piezoelectric properties of samples were investigated. The research showed that an increase in the porosity led to reduced dielectric constant as well as enhanced hydrostatic figures of merit (dh·gh). The effect of porosity on dielectric constant can be predicted by the Okazaki experiential formula and Banno model under certain conditions. An increase in grain size increases the dielectric constant, piezoelectric coefficient and hydrostatic figures of merit, which can be explained by the Okazaki space-charge theory. For the sample with 10 wt% PMMA additions sintered at 1300℃, the porosity is 34% and the longitudinal piezoelectric coefficient (d33) is very close to that of dense PZT ceramics, while the hydrostatic figures of merit (dh·gh) is about fifteen times greater than that of dense PZT ceramics. Compared with PZT-polymer composites, the dielectric constant and piezoelectric coefficient of 34% porous PZT sintered at 1300℃ is much higher and can be more efficient in resisting the interference from the ambient medium.

Effect of porosity on dielectric properties and microstructure of porous PZT ceramics

Porous piezoelectric materials are of great interest because of their high hydrostatic figure of merit and low sound velocity, which results in to low acoustic impedance and efficient coupling with medium. Porous lead zirconate titanate (PZT) ceramics with varying porosity was developed using polymethyl methacrylate by burnable plastic spheres (BURPS) process. The porous PZT ceramics were characterized for dielectric constant ( ɛ), dielectric loss factor (tan δ), hydrostatic charge ( d h) and voltage ( g h) coefficients and microstructure. The effect of the porous microstructure on the dielectric constant and loss factor at frequencies of 10–10 5 Hz are discussed in this paper.

Characterization and microstructure of porous lead zirconate titanate ceramics

Porous lead zirconate titanate (PZT) ceramics are widely used because of their low acoustic impedance, high figure of merit and high hydrostatic sensitivity. In the present work, porous PZT ceramics were fabricated by incorporating polyethylene oxide (PEO) as pore-forming agent. Both PZT powder and PEO were mixed with a binder at different ratios and compaction was carried out. The samples were slowly heated to remove the pore-forming agent and binder without cracks, followed by controlled sintering and electrode forming. Samples were poled using corona poling technique. The ferroelectric properties and microstructure of the prepared ceramics were characterized. The correlation of porosity with microstructure and ferroelectric properties were discussed.

Investigation on the microstructure and ferroelectric properties of porous PZT ceramics

In the present work, porous lead zirconate titanate (PZT) ceramics were fabricated by introducing pore-forming agent polymethyl methacrylate (PMMA) and sintering green compacts at low temperature. The phase, the microstructure, and the ferroelectric properties of the prepared ceramics were characterized. The correlation of microstructure with ferroelectric properties was discussed. The porosity increased with increase in the added PMMA content at a given sintering temperature or decreasing the sintering temperature at a fixed added PMMA content. The dielectric constant and the dielectric loss of the investigated samples decreased with increase in the frequency. The dielectric constant decreased and the dielectric loss increased with the increase in the addition content of PMMA at fixed frequency and sintering temperature. At same porosity, the sample with macropores showed lower dielectric constant and dielectric loss, compared to the sample with micropores.