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.     

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.     

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.     

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.     

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.     

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.     

The effect of nano-sized BNBT on microstructure and dielectric/piezoelectric properties

(Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ (abbreviated as BNBT6) ceramic of near MPB composition was synthesized by two different processes. The first one is the addition of pre-synthesized BaTiO₃ and pre-milled Bi₂O₃, Na₂CO₃, BaCO₃ powders and calcination powder milled with a high energy milling machine in order to obtain a nano-particle size. The second one is a conventional one to compare with the former process. The pre-milling and the pre-synthesis process of raw materials lowered the calcination temperature to the extent of 59 °C as compared with conventionally fabricated BNBT6. The particle size of the powder exposed to heavy high energy milling reduced to 50–70 nm, whereas that of the conventionally ball-milled powder without the pre-milling and the pre-synthesis process had a larger size of 280 nm. To investigate the effects of the modified process on the characteristic of BNBT6 ceramics, the dielectric and the piezoelectric properties of sintered specimens fabricated by the two different processes were evaluated. It was found that the properties of the nano-sized BNBT6 ceramic near the MPB composition were increased by the modified mixing and milling method, showing superior characteristics in terms of the piezoelectric/dielectric constant and sintering density compared with those of the conventional process. The modified mixing and milling method was considered to be a new and promising process for lead-free piezoelectric ceramics owing to their excellent piezoelectric/dielectric properties.     

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).     

Hard/soft effects of multivalence co-dopants in correlation with their location in PZT ceramics

Piezoelectric hard/soft effects of multivalence co-dopants (Sb and Mn) in correlation with their location in the lattice, were investigated in PZT ceramics, prepared by conventional ceramic technology, with the following compositions: Pb_0.98Sr_0.02 ((Ti_0.49Zr_0.51)_1-0.015-xMn_0.015Sb_x)O₃ with x = 0, 0.005, 0.01, 0.02, 0.03, where antimony was initially assumed to substitute for Ti/Zr ions. The antimony valence state was found to be +3 in all samples by X-ray Photoelectron Spectroscopy investigations. The Electron Paramagnetic Resonance spectra evidenced a steep enhancement of the Mn²⁺ concentration upon increasing antimony doping level, explained by a charge compensation mechanism, between the Sb³⁺ ions substituting Pb²⁺ at the A-sites and the Mn²⁺ ions, localized at the B-sites. The incorporation of Sb³⁺ at the A-site of the PZT lattice is also supported by the variation of the lattice parameters, determined by X-ray Diffraction, with the increasing Sb concentration. The investigation of the dielectric, electromechanical and ferroelectric properties evidenced a hard piezoelectric behavior, mainly attributed to the presence of large sized Mn²⁺ ions, localized at B-sites. Our results prove that the piezoelectric hard/soft response is decisively influenced by the interplay between multiple valence states and locations of the co-dopants, on one hand, and the charge compensation mechanisms, on the other hand. This provides indirect information about the location of some co-dopants which can substitute for both cationic sites in the PZT based ceramics.     

Effects of LiF addition on microstructure and dielectric properties of CaCu3Ti4O12 ceramics

The effects of small amounts of lithium fluoride sintering aid on the microstructure and dielectric properties of CaCu₃Ti₄O₁₂ (CCTO) ceramics were investigated. CCTO polycrystalline ceramics with 0.5 and 1.0 mol% LiF, and without additive were prepared by solid state synthesis. Good densification (>90% of the theoretical density) was obtained for all prepared materials. Specimens without the sintering aid and sintered at 1090 °C exhibit secondary phases as an outcome of the decomposition reaction. The mean grain size is controlled by the amount of LiF in specimens containing the additive. Impedance spectroscopy measurements on CaCu₃Ti₄O₁₂ ceramics evidence the electrically heterogeneous nature of this material consisting of semiconductor grains along with insulating grain boundaries. The activation energy for grain boundary conduction is lower for specimens prepared with the additive, and the electric permittivity reached 53,000 for 0.5 mol% LiF containing CCTO.     

Highly porous and hierarchical MgAl2O4 ceramics with improved pore connectivity prepared from gelled particle-stabilized foams

Ultralight ceramics with striking mechanical properties and improved pore connectivity could have wide applications in areas ranging from catalyst support to hot gas filtration. However, creating such materials has proven to be a challenging target. This work demonstrated a novel methodology to prepare porous MgAl₂O₄ ceramics by calcining gelled MgO–Al₂O₃–SiO₂ particle-stabilized foams. The striking green strength of dried foams can be achieved as a consequence of MgO hydration and subsequent formation of gelled Mg(OH)₂ and MgO–SiO₂–H₂O skeleton. The decomposition of colloidal substance at elevated temperature resulted in the formation of small pores on the cell wall, thus forming the hierarchical porous architecture and improving the pore connectivity. The highly porous MgAl₂O₄ ceramics fired at 1600°C possessed the integrated properties of ultrahigh porosity (87.0%), improved pore connectivity and satisfactory compressive strength (7.93 MPa), showing great potential to be used in multiple industrial fields.     

Effects of addition of Pb(Y1/2Nb1/2)O3 (PYN) on microstructure and piezoelectric properties of Pb(Zr0.53Ti0.47)O3

Pure and Pb(Y_1/2Nb_1/2)O₃ (PYN)-doped Pb(Zr_0.53Ti_0.47)O₃ have been characterized. The samples were prepared by conventional mixed-oxide ceramic technology. PYN dopant was added to PZT at content levels ranging from 1 to 2.5 mol%. The microstructures of the samples were examined using SEM and TEM. The average grain size was observed to decrease as the dopant content increased. Herringbone-like and wedge-shaped domain patterns were observed in all the samples. The piezoelectric properties of PZT were greatly improved by the addition of PYN. The highest piezoelectric constant d₃₁ was nearly twice that of pure PZT.     

Effects of mechanical activation and two-step sintering on the structure and electrical properties of cordierite-based ceramics

The mechanical activation can help reduce production costs and modify cordierite-based materials. In this study, the structure and electrical properties of the mechanically activated MgO-Al₂O₃-SiO₂ system have been analyzed. The mixtures of MgO-Al₂O₃-SiO₂ powders were mechanically activated in a planetary ball mill for time periods ranging from 0 to 160 min. Structural investigations were performed on the obtained powders. The effects of activation and a two-step sintering process on the microstructure and crystal structure were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The thermal stability was analyzed using DTA. Electrical measurements showed variations of the dielectric constant (ε_r) and loss tangent (tan δ) as a function of the time of mechanical treatment.     

Temperature dependence of macroscopic and microscopic PZT properties studied by thermo-mechanical analysis,dielectric measurements and X-ray diffraction

The main objective of the paper is to point out the influence of composition and of poling state (poled and unpoled samples) on the evolution of various parameters (?_r, dilatation coefficients, lattice parameters) at different scales (lattice, bulk) using X-ray diffraction (XRD), thermo-mechanical analysis (TMA) and dielectric methods. The transition temperatures have been determined from the above measurements and compared. The composition has an influence on the transition temperature and not on the dilatation coefficient value. The poling state influences only the macroscopic dilatation evolution and not the value of the transition temperature. A scale effect is only observed on majoritary tetragonal compositions which show different values of transition temperatures from microscopic and macroscopic methods.     

SnO2 modified PNN-PZT ceramics with ultra-high piezoelectric and dielectric properties

In this work, a two-step solid-state reaction method is used to prepare the 0.55 Pb(Ni_1/3Nb_2/3)O₃-0.135PbZrO₃-0.315PbTiO₃/xSnO₂ (PNN-PZT/xSnO₂) ceramics. The influences of SnO₂ on the crystalline structure, electromechanical properties, and temperature stability of PNN-PZT ceramics were studied in detail. The results demonstrate that the Sn⁴⁺ ions are successfully introduced into the PNN-PZT crystalline lattice and substitute B-site Ni²⁺ and Zr⁴⁺. The x = 0.0025 ceramic with the coexistence of rhombohedral, tetragonal, and pseudocubic phases exhibits the optimized comprehensive properties: the quasi-static piezoelectric constant d₃₃, large-signal d₃₃*, electromechanical coupling coefficients k_p and k_t, free dielectric constant ε_r, and mechanical quality factor Q_m are 1123 pC/N, 1250 p.m./V, 0.63, 0.54, 9529, and 57, respectively. Meanwhile, the Curie temperature for this composition is 103 °C, almost maintaining the same level as the PNN-PZT matrix. After annealing at 75 °C, the retained d₃₃ of x = 0.0025 ceramic is as high as 975 pC/N, superior to the PNN-PZT matrix (retained d₃₃ ≈ 873 pC/N). Our results provide a promising piezoelectric material for board bandwidth, high sensitivity, and miniaturized medical ultrasonic transducers applications.     

Effects of compressive stress on the dielectric properties of PIN–PT ceramics

Lead indium niobate, Pb(In_1/2Nb_1/2)O₃ (PIN), is an interesting ferroelectric due to a transition from a disordered to an ordered state by long-time thermal annealing. However, the temperature related to the maximum dielectric constant (T_max) of PIN in relaxor phase is low (at 1 kHz, T_max = 66 °C). In this study, lead titanate PbTiO₃ (PT) was added to PIN with compositions (1 − x)PIN–xPT (for x = 0.1–0.5) to increase their T_max. The influence of stress on dielectric properties of (1 − x)PIN–PT ceramics was then investigated. The dielectric properties were measured under various uniaxial compressive stresses up to 400 MPa. The results showed the reduction of dielectric constant in 0.9PIN–0.1PT with superimposed compression load. For other compositions, dielectric constants first increased with compressive stress, then decreased when the stress was further increased up to 400 MPa. The loss tangent of all composition was found to decrease with increasing compressive stress.     

Direct observation of domain switching and crack nucleation in a piezoelectric material

The effect of an electric field on domain switching and fatigue induced crack nucleation and growth in a piezoelectric material of nominal composition Pb(Zr_0.5, Ti_0.5)O₃ has been investigated. The ceramic was subjected to localised static and cyclic electric fields, which were applied via pairs of closely spaced surface-mounted electrodes, while simultaneously imaging the microstructure in the SEM. Electric field–polarisation hysteresis loops were also collected from the local region using the same electrodes.Domain wall mobility was observed above a threshold electric field strength, as was microcracking. Cracks were seen to nucleate at grain boundaries, and were sometimes associated with microstructural features, such as pores. Crack propagation was mainly intergranular, and occurred preferentially in a direction parallel to the local field direction. Transgranular fracture was also observed, with the crack path being influenced by interaction with domain boundaries. Factors affecting domain switching and crack propagation are discussed in the context of the locally applied electric field.     

Phase transition,microstructure and electrical properties of Fe doped Ba0.70Ca0.30TiO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics of Ba_0.70Ca_0.30Ti_1?xFe_xO₃ (x=0–0.03) have been synthesized by a conventional solid state reaction method. The influence of Fe content on the microstructure, phase transition, dielectric, ferroelectric, and piezoelectric properties is investigated systematically. The ceramics with x≤0.02 are diphasic composites of tetragonal Ba_0.80Ca_0.20TiO₃:Fe and orthorhombic Ba_0.07Ca_0.93TiO₃:Fe solid solutions. The tetragonal phase is gradually suppressed as x increases, the ceramic with x=0.03 is found to have diphasic pseudocubic and orthorhombic phases. And the grain size is dependent on Fe content significantly. Introduction of Fe at B-sites improves the densification and decreases the sintering temperature. As x increases from 0 to 0.03, the room temperature relative dielectric permittivity enhances, dielectric loss decreases, and the Curie temperature decreases monotonically from 128 °C to 58 °C. However, the ferroelectricity enhances slightly and reaches the maximum near x=0.005, and then weakens with increasing x. On the other hand, the piezoelectric coefficient (d₃₃) and the electromechanical coupling coefficient (k_p) decrease simultaneously with increasing x, whereas the mechanical quality factor (Q_m) increases significantly. The structure–electrical properties relationship is discussed intensively to give more information on (Ba,Ca)TiO₃-based lead-free piezoelectric ceramics.