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

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 (ε_r), a moderate decline in the longitudinal piezoelectric strain coefficient (d₃₃) and a rapid decline in the transverse piezoelectric strain coefficient (d₃₁), 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.     

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.     

Effects of pore shape and porosity on the properties of porous PZT 95/5 ceramics

Porous lead zirconate titanate (PZT 95/5) ferroelectric ceramics were prepared by sintering compacts consisting of PZT and pore formers. The piezoelectric, dielectric and ferroelectric properties of porous PZT ceramics were investigated as a function of pore shape and porosity. Piezoelectric coefficient (d₃₃), dielectric constant (ɛ₃₃) and remnant polarization (P_r) decreased with an increase in porosity, and the porous PZT ceramics with spherical pores exhibited better properties than that with irregular pores. Furthermore, the electrical conductivities of PZT ceramics were investigated to explain the phenomena that porous PZT ceramics exhibited lower dielectric loss (tan δ) than dense PZT ceramics in the temperature range from 250 to 500 °C.     

Microstructure,electrical and mechanical properties of MgO nanoparticles-reinforced porous PZT 95/5 ferroelectric ceramics

Porous Pb (Zr_0.95Ti_0.05) O₃/xMgO (PZT/MgO, x=0, 0.1, 0.2, 0.5 and 1.0 wt%) ferroelectric ceramics were prepared with MgO nanoparticles as reinforcing phase. The effects of MgO nanoparticles on the phase, microstructure, electrical and mechanical properties of as-prepared ceramics were investigated. The results show that the grain size is reduced obviously when increasing the amount of MgO. Compared with pure porous PZT, T_C of MgO-added PZT ceramics shifts to higher temperature. Moreover, dielectric, ferroelectric and piezoelectric properties show no much degradation. Further, PZT/MgO ceramics possess enhanced mechanical properties compared to pure porous PZT ceramics, the largest increment of the fracture toughness and hardness being 31.3% and 19.8%, respectively. The optimal electrical and mechanical properties are obtained with the addition of less than 0.5 wt% MgO nanoparticles.     

Composition design,phase transitions and electrical properties of Sr2+-substituted xPZN–0.1PNN–(0.9−x)PZT piezoelectric ceramics

The influences of PZN content and Sr²⁺ substitution on the structure and electrical properties of Pb(Zn_1/3Nb_2/3)O₃–Pb(Ni_1/3Nb_2/3)O₃–Pb(Zr_0.52Ti_0.48)O₃ (abbreviated as PZN–PNN–PZT) piezoelectric ceramics were studied. All as-prepared PZN–PNN–PZT ceramics presented single phase of perovskite structure, while higher PZN contents favored rhombohedral symmetry and larger grain size. Meanwhile, with the increase in Sr²⁺ content, the phase structure changed from a mix of tetragonal and rhombohedral symmetries to a pure rhombohedral symmetry. Although the ferroelectric Curie temperature (T_C) was decreased with increasing the PZN and Sr²⁺ contents, the piezoelectric constant (d₃₃) exhibited the opposite trend. As a result, optimum comprehensive electrical properties were obtained in the 0.1PZN–0.1PNN–0.8PZT composition with 10 mol% Sr²⁺ substitution: d₃₃~800 pC/N, k_p ~0.65, ɛ_r~4081, T_C~176 °C, P_r~30.92 µC/cm². Thus, the 10 mol% Sr²⁺-substituted 0.1PZN–0.1PNN–0.8PZT ceramic is a promising candidate for high performance applications.     

Low temperature sintering and high piezoelectric properties of strontium doped PNZT–PNN ceramics processed via the columbite route

This study investigated the influence of strontium doping on both the sintering behavior and the piezoelectric properties of PNZT–PNN ceramics. The piezoelectric ceramics was produced by solid state reaction between metallic oxides, strontium carbonates (SrCO₃) and oxides precursors. NiNb₂O₆ precursors were mixed with the oxides to avoid the large-scale formation of pyrochlore phases during the sintering process and to favor the formation of the perovskite structure. Sintering experiments were accomplished between 900 °C and 1100 °C for PNZT–PNN with 0–4 mol% strontium. Dilatometer curves indicated that the densification of these samples occurs by 850 °C and the electromechanical characterization showed that strontium doping enhances the soft piezoelectric properties of the PZT–PNN ceramics.Consequently, a sintering temperature of 900 °C is sufficient to obtain doped PZT–PNN tablets with 99% of the theoretical density and excellent soft piezoelectric properties (ɛ_r > 4000; K_p > 60; d₃₃ > 1000 pm/V). This makes those ceramics suitable for the construction of high efficiency actuators with low sintering temperature. The low Curie temperature is the only drawback of this material for some applications such as engine fuel injection.     

Low temperature sintering and dielectric properties of (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3−xCu2+ ceramics obtained by the sol-gel technique

Lead-free Cu²⁺-modified (Ba_0.85Ca_0.15)(Ti_0.9Zr_0.1)O₃ (BCZT−xCu²⁺) piezoelectric ceramics was synthesized by sol-gel method. The effects of Cu²⁺ additions on sintering characteristics, the phase structure, microstructure, electrical properties and complex impedance characteristic were investigated systematically. The XRD patterns exhibited a pure perovskite structure without impurity phase in all samples. SEM micrographs, temperature dependence of dielectric constant and polarization-electric field (P-E) hysteresis loops indicated that a small amount of Cu²⁺ addition affected the properties obviously. The results revealed that the addition of Cu²⁺ significantly improved the sinterability of BCZT ceramics which resulted in a reduction of sintering temperature from 1440 °C to 1230 °C. The TG-DSC was analyzed to verify the reaction process of BCZT−Cu²⁺ materials. (Ba_0.85Ca_0.15)(Ti_0.9Zr_0.1)O₃ ceramics with x=0.020 Cu²⁺ exhibited good electrical properties: ε_m=12,112, T_c=360 K, ε_r=2614, tan δ=0.026, K_p=0.47 and d₃₃=382 pC/N. The results indicated that Cu²⁺-modified BCZT ceramics could be a promising candidate for commercial purposes.     

Effect of CaO addition on the structure and electrical conductivity of the pyrochlore-type GdSmZr2O7

Polycrystalline GdSm_1?xCa_xZr₂O_7?x/2 (0 ≤ x ≤ 0.20) ceramics have been prepared by the solid-state reaction method. The effects of CaO addition on the microstructure and electrical properties of the pyrochlore-type GdSmZr₂O₇ ceramic were investigated. GdSm_1?xCa_xZr₂O_7?x/2 (x ≤ 0.05) ceramics exhibit a pyrochlore-type structure; however, GdSm_1?xCa_xZr₂O_7?x/2 (0.10 ≤ x ≤ 0.20) ceramics consist of the pyrochlore-type structure and a small amount of CaZrO₃. The total conductivity of GdSm_1?xCa_xZr₂O_7?x/2 ceramics follows the Arrhenius relation, and gradually increases with increasing temperature from 723 to 1173 K. GdSm_1?xCa_xZr₂O_7?x/2 ceramics are oxide-ion conductors in the oxygen partial pressure range of 1.0 × 10^?4–1.0 atm at each test temperature. The highest total conductivity is about 1.20 × 10^?2 S cm^?1 at 1173 K for the GdSm_0.9Ca_0.1Zr₂O_6.95 ceramic.     

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 (ɛ₃₃) and longitudinal piezoelectric coefficient (d₃₃) 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.     

Reaction sintering of lead zinc niobate–lead zirconate titanate ceramics

Lead zinc niobate (PZN)–lead zirconate titanate (PZT) ceramics were produced by the reaction-sintering process. The specimens were prepared directly from a mixture of their constituent oxides without any calcination step. When 50% PZN was added to tetragonal Pb(Zr_0.47Ti_0.53)O₃ ceramics, the densities and electrical properties were found to be optimal (ρ = 7.91 g/cm³, K = 1947 at 1 kHz and room temperature, d₃₃ = 530 pC/N, k_p = 0.61). However, the specimen containing more than 50% PZN showed reduced density and decreased electrical properties, due to the formation of pyrochlore phases. The improved densification behavior of the reaction-sintering process was attributed to the enhanced diffusion of lattice defects, which were created by differences in the ionic valence of the B-sites ions of the perovskite structure.     

Phase,microstructure and ferroelectric properties of new complex-structured ferroelectric ceramics in the PZT–SBN system

This study aimed to fabricate and characterize new complex-structured ceramics with formula (1-x)Pb(Zr_0.52Ti_0.48)O₃–xSrBi₂Nb₂O₉ or (1-x)PZT–xSBN (where x=0, 0.1, 0.3 and 0.5 weight fraction). The ceramics were prepared by a solid-state mixed-oxide method and sintered at temperatures between 1000 and 1250 °C. Optimum sintering temperature for this system was found to be 1050 °C for 3 h dwell time. X-ray diffraction patterns of (1-x)PZT–xSBN powders showed peak intensities of two-phase mixture corresponding to the relative amount of each phase as a result of SBN addition. Microstructure of (1-x)PZT–xSBN ceramics showed a variation in grain shape and grain size. The small addition of SBN (x=0.1) was also found to improve ferroelectric properties of pure PZT ceramic.     

“Dark hole” cure in Ba4.2Nd9.2Ti18O54 microwave dielectric ceramics

Large size Ba_4.2Nd_9.2Ti₁₈O₅₄ (BNT) ceramics doped with MnCO₃, CuO and CoO were prepared by the conventional solid-state method. Only a single BaNd₂Ti₄O₁₂ phase was formed in all samples. No second phase was found in the XRD patterns. The bulk density increases slightly because of the dopants. The SEM results showed that the grain size of Mn²⁺and Cu²⁺-doped BNT ceramics became larger with the increasing amount of dopants. The permittivity of all samples stays the same. However, the Q×f value of BNT ceramics increases by doping, especially with Mn²⁺ ions. The conductivity of BNT ceramic doped with Mn²⁺(0.5 mol‰) under high temperature is lower than that without doping. There are fewer defects in Mn²⁺-doped BNT ceramics. The XPS results indicated that Ti reduction was suppressed in BNT ceramics doped with 0.5 mol‰ Mn²⁺. BNT ceramics doped with 0.5 mol‰ Mn²⁺ ions sintered at 1320 °C for 2 h exhibited good microwave dielectric properties, with ε_r=88.67, Q×f=7408 GHz and τf = 82.98 ppm/°C.     

Shift of morphotropic phase boundary in high-performance fine-grained PZN–PZT ceramics

The fine-grained xPb(Zn_1/3Nb_2/3)O₃–(1 − x)Pb(Zr_0.47Ti_0.53)O₃ system has been prepared from submicron precursor powders obtained by high-energy ball milling method. The addition of PZN induces a decrease of grain size from an initial micron scale to a submicron scale, accompanying with the phase transition from tetragonal to morphotropic phase boundary (MPB), and then rhombohedral side. Interestingly, compared to the former published data for coarse-grained ceramic, the MPB has shifted from 50% to 30% PZN content side due to the enhancement of the internal stress for fine-grained ceramic. The enhanced electrical and mechanical performances are closely associated with the phase structure and grain size. A high piezoelectric property (d₃₃ = 380 pC/N and k_p = 0.49) as well as mechanical performance (H_v = 5.0 GPa and K_IC = 1.33 MPa m^1/2) were obtained simultaneously for the MPB 0.3PZN–0.7PZT ceramics with an average grain size of 0.65 μm.     

Electrical and transparent properties induced by structural modulation in (Sr0.925Ca0.075)2.5–0.5xNa xNb5O15 ceramics

The effects of Na⁺ concentration on the microstructural, dielectric, ferroelectric and transparent properties of (Sr_0.925Ca_0.075)_2.5–0.5xNa _xNb₅O₁₅ (SCNN; 0.4 ≤ x ≤ 1.0) ceramics prepared using a conventional solid-state reaction method were investigated. X-ray diffraction results showed that the phase structure transitioned from tetragonal to orthorhombic tungsten bronze along with the structural type changing from ‘unfilled’ to ‘filled’ state. The NbO₆ octahedron became more distorted and had higher interaction strength when introducing Na⁺ in A-sites to decrease the structural vacancies, leading to the improvement of dielectric and ferroelectric properties. The dielectric spectra of all specimens showed two broad dielectric anomalies: a high-temperature anomaly (the ferroelectric phase transition) and a low-temperature anomaly caused by the subtle structural effects in ‘unfilled’ SCNN ceramics, which evolved into the ferroelastic phase transition in ‘filled’ SCNN ceramics.     

Effect of BaCu(B2O5) on the sintering and microwave dielectric properties of Ca0.4Li0.3Sm0.05Nd0.25TiO3 ceramics

The sintering behaviors and microwave dielectric properties of the Ca_0.4Li_0.3Sm_0.05Nd_0.25TiO₃ (abbreviated CLSNT) ceramics with different amounts of BaCu(B₂O₅) addition were investigated in this paper. Adding BaCu(B₂O₅) to CLSNT lowered its sintering temperature from 1300 °C to 925 °C. No secondary phase was observed in the CLSNT ceramics and complete solid solution of the complex perovskite phase was confirmed. The CLSNT ceramics with small amounts of BaCu(B₂O₅) addition could be well sintered at 925 °C without much degradation in the microwave dielectric properties. Especially, the 1.75 wt.% BaCu(B₂O₅)-doped CLSNT ceramic sample sintered at 925 °C for 3 h had optimum microwave dielectric properties of ε_r = 93.5 ± 3.2, Q × f = 6486 ± 434 GHz, and τ_f = 5 ± 1.5 ppm/°C (at 3–4 GHz), enabling it a promising candidate material for LTCC applications. Obviously, BaCu(B₂O₅) could be a suitable sintering aid to facilitate the densification and microwave dielectric properties of the CLSNT ceramics.     

Phase-formation,microstructure, and piezoelectric/dielectric properties of BiYO3-doped Pb(Zr0.53Ti0.47)O3 for piezoelectric energy harvesting devices

This paper proposes a method for the composition and synthesis of lead zirconate titanate (PZT) piezoelectric ceramic for use in energy harvesting systems. The proposed material consists of (1?x)Pb(Zr_0.53Ti_0.47)O₃–xBiYO₃ [PZT–BY(x)] (x=0, 0.01, 0.02, 0.03, 0.04, and 0.05 mol) ceramics near the morphotropic phase boundary (MPB) region, prepared by a solid-state mixed-oxide method. The optimum sintering temperature was found to be 1160 °C, which produced high relative density for all specimens (96% of the theoretical density). Second phases were found to precipitate in the composition containing x≥0.01 mol of BY. It is shown that the addition of BY inhibits grain growth, and exhibits a denser and finer microstructure than those in the un-doped state. Fracture surface observation revealed predominant intergranular fracture for x=0 and x=0.01, while a mixed mode of transgranular and intergranular fracture appeared for x≥0.02. The optimal doping level was found to be x=0.01, for which a dielectric constant (K₃₃^T) of 750, a Curie temperature (T_C) of 373 °C, a remnant polarization (P_r) of 50 µC/cm², a piezoelectric constant (d₃₃) of 350 pC/N, and an electro-mechanical coupling factor (k_p) of 65% were obtained. In addition, the piezoelectric voltage constant (g₃₃), and transduction coefficient (d₃₃×g₃₃) of PZT–BY(x) ceramics have been calculated. The ceramic PZT–BY(0.01) shows a considerably lower K₃₃^T value, but higher d₃₃ and k_p. Therefore, the maximum transduction coefficient (d₃₃×g₃₃) of 18,549×10^?15 m²/N was obtained for PZT–BY(0.01). The large (d₃₃×g₃₃) indicates that the PZT–BY(0.01) ceramic is a good candidate material for energy harvesting devices.     

The structure and properties of 0.95MgTiO3–0.05CaTiO3 ceramics co-doped with ZnO–ZrO2

The (Mg_0.93Ca_0.05Zn_0.02)(Ti_1?xZr_x)O₃ ceramics were prepared by conventional solid-state route. The dielectric properties and structure of (Mg_0.93Ca_0.05Zn_0.02)(Ti_1?xZr_x)O₃ ceramics were investigated. It has been found that MgTiO₃ and CaTiO₃ are the main phases and a second phase CaZrTi₂O₇ appeared in 95MCT ceramics co-doped with Zn–Zr. With Zn–Zr additive, the sintering temperature of 95MCT ceramics can be reduced to 1300 °C, and adjust the temperature coefficient of dielectric constant. With the increasing of Zr content, dielectric constant ?_r decrease from 22.6 to 19.91 and the temperature coefficient of dielectric constant α_c from 5.93 to 2.52 ppm/°C when x = 0.01, 0.02, 0.03 and 0.04 mol respectively. The 95MCT ceramics with x = 0.02 has a dielectric constant ?_r of 22.02, a dielectric loss of 2.78 × 10^?4 and a temperature coefficient of dielectric constant α_c value of 2.98 ppm/°C.     

Effect of high alumina cement on permeability and structure properties of ZrO2 composites

Porous ZrO₂ based ceramics are widely used for filtration/separation processes due to the good chemical and thermal stability. For these applications it is desirable that the material have a controlled porous structure in order to obtain good permeability. In this study Ca stabilized ZrO₂ composites were developed from a starting mixture of pure ZrO₂ containing different mole proportions of calcium aluminate cement. Ceramics disks were uniaxially pressed and subsequently sintered at 1300–1450 °C. The influence of process parameters such as chemical compositions and sintering temperature on textural characteristics (volume fraction of pores, pore size distribution) and permeability was followed by apparent density measurements, Hg porosimetry and N₂ permeation, respectively. Sintered microstructure was examined by scanning electron microscopy SEM. The XRD analysis showed that m-ZrO₂ transformed to tetragonal and/or cubic ZrO₂, these phases probably coexisted at relatively low CaO addition. For 30 mol% addition, amount of the cubic Ca_0.15Zr_0.85O_1.85 phase appreciably increased. At 50 mol% CaO, CA₂ was the major phase of the composite with minor CaZrO₃ formation whereas relative content c-ZrO₂ is slightly reduced.The composites had 30–40 vol% porosity with typical pore radius of 1–1.3 μm and the corresponding Darcian permeability k₁ values varied between 2 and 4 × 10^?14 m², such structure parameters slightly increased for high cement addition. The k₁ of ceramics produced from 50 mol% CaO composition remained nearly constant up to 1450 °C due to similar densification degree. The experimental permeability dependence on pore structure parameters as well as the comparison with the value estimated by Ergun's equation are showed.     

Effect of ZnO nano-particulate modification on properties of PZT–BLT ceramics

This research was conducted to study the effect of ZnO nano-particulate modification on properties of Pb(Zr_0.52Ti_0.48)O₃ (PZT)–(Bi_3.25La_0.75)Ti₃O₁₂ (BLT) ceramics prepared by a mixed-oxide solid-state sintering method. ZnO nano-particulate was added into PZT–BLT ceramics to obtain PZT–BLT/xZnO (x = 0, 0.1, 0.5 and 1.0 wt%). The PZT–BLT/xZnO ceramics were investigated in terms of phase, microstructure, physical, electrical, and mechanical properties. Tetragonality of PZT–BLT crystal structure tended to increase with increasing ZnO content. ZnO addition obviously increased the density of PZT–BLT ceramics while the grain size slightly decreased. Intergranular fracture mode was observed for pure PZT–BLT ceramic while the samples contained ZnO nano-particles showed a mixed-mode inter-/trans-granular fracture. Addition of ZnO also affected hardness and fracture toughness values. Addition of ZnO nano-particulate into PZT–BLT ceramics was found to improve room temperature dielectric constant but did not have a significant effect on ferroelectric properties. These observed results were expected to be caused by the behaviors similar to a donor-doped system.     

Ferroelectric properties of Pb(Zr0.52Ti0.48)O3–Bi3.25La0.75Ti3O12 ceramics

The ceramic samples of compound (1 ? x)Pb(Zr_0.52Ti_0.48)O₃–xBi_3.25La_0.75Ti₃O₁₂ (when x = 0, 0.03, 0.05, 0.07, 0.10, 0.15 and 0.20) were prepared by a solid-state mixed oxide method. X-ray diffraction analysis showed that complete solid solutions occurred for all compositions. Perovskite phase with tetragonal crystal structure and corresponding lattice distortion was observed. Scanning electron micrographs of sample surfaces showed equiaxed grains for all compositions. Ferroelectric measurements revealed that the addition of small amount of BLT (x = 0.03) showed high remanent polarization (～33.5 μC cm^?2) and low coercive field (～2.74 kV mm^?1). Further increasing BLT content could maintain ferroelectric properties of PZT–BLT ceramics. Based on this study, ferroelectric properties of this PZT–BLT ceramic system can be improved for being further used in ferroelectric memory applications.