Effects of an Electric Field on the Fracture Toughness of Poled Lead Zirconate Titanate Ceramics

Compact tension tests and indentation-fracture tests have been conducted to study the effects of an applied electric field on the fracture toughness ( K _{I C} ) of poled commercial lead zirconate titanate (PZT) ceramics. The experimental results show that an applied electric field, either parallel or antiparallel to the poling direction, considerably reduces the K _{I C} value of the PZT ceramics. The reduction in K _{I C} for a negative field is larger than that for a positive field of the same strength. The failure mode in the PZT ceramics is basically transgranular, insensitive to the applied electric field.     

Subcritical Crack Growth in Lead Zirconate Titanate

Subcritical crack growth in terms of velocity–stress intensity factor ( v – K ) curves in lead zirconate titanate (PZT) were experimentally characterized on poled and unpoled compact tension specimens. The poled specimens were tested under open- and short-circuit electrical boundary conditions, which resulted in an increase in fracture toughness by 0.2 MPa·m^1/2 for the accessible velocity range ( v = 10⁻⁹ to 10⁻⁴ m/s) in the open-circuit case. Subcritical crack growth of unpoled specimens was obtained under ambient (relative humidity = 35%) and dry (relative humidity ∼ 0.02%) conditions over a regime in stress intensity factor of 0.5 MPa·m^1/2.     

Crack-Growth-Velocity-Dependent R-Curve Behavior in Lead Zirconate Titanate

Crack-velocity ( v – K ) curves and crack-resistance ( R ) curves for unpoled ferroelectric and ferroelastic lead zirconate titanate (PZT) were determined for long cracks in compact-tension (CT) geometry using an in situ fracture device on the stage of an optical microscope. The steady-state crack length and the plateau value of R -curves measured at controlled constant velocities increased with increased velocity. The plateau value for 10⁻⁶ m/s was 1.2 MPa·m^1/2 after 1.3 mm of crack extension and for 10⁻⁴ m/s was 1.4 MPa·m^1/2 after 2.2 mm.     

Electrophoretic Deposition of Lead Zirconate Titanate Ceramics

Electrophoretic deposition (EPD) of submicrometer lead zirconate titanate (PZT) powders in ethanol was conducted to form thick green PZT films up to 160 μm thick. The PZT colloid stability, as a function of pH, was studied by zeta-potential measurement. The electrical condition of the suspension was quantified by conductivity measurement at various pH values. The effect of different applied current densities on the deposition mass was investigated. A kinetic model for the constant-current-density EPD process, taking into account the particle concentration variation, was also examined, based on the experimental results obtained in the present work. An empirical relationship between the kinetic constant and the applied current density has been proposed.     

Synthesis of Lead Nickel Niobate–Lead Zirconate Titanate Solid Solutions by a B-site Precursor Method

A modified processing method for lead nickel niobate–lead zirconate titanate (Pb(Ni_1/3Nb_2/3)O₃–Pb(Zr,Ti)O₃, PNN–PZT) solid solutions is presented. This method is based on the high-temperature synthesis of a precursor that contains all the B-site cations (Ti, Zr, Ni, and Nb). This synthesis yields a diphasic mixture that contains a ZrTiO₄-like phase and a rutile-like phase. Both phases exhibit a cationic valence of 4; thus, it is concluded that the mixing of Ni and Nb cations is adequate for the preparation of PNN–PZT solid solutions. Indeed, a pure perovskite phase has been obtained after calcination with lead oxide for compositions that contain 40 and 50 mol% PNN. Moreover, their electromechanical properties have been shown to be superior to values reported for standard columbite routes. This conclusion has been interpreted in terms of enhanced chemical homogeneity.     

Lead Zirconate Titanate Particle Dispersion in Thick-Film Ink Formulations

Diverse device applications for lead zirconate titanate (PZT) ceramics in thick-film form are currently in active development. In the present study, the particle dispersion properties of thick-film ink formulations containing PZT powder have been determined using rheological measurements. Although all of the eight commercially available dispersants tested are more effective than the terpineol solvent alone in decreasing attractive interparticle forces in suspensions, the best dispersant identified for hard and soft PZT powders is a phosphate ester oligomer. This dispersant is extremely efficient, and its use in thick-film ink formulations results in viscosity decreases of 50% at low shear rates (10 s⁻¹) and 30% at high shear rates (100 s⁻¹) compared with current ink formulations containing no dispersant. The effects upon rheology of the order of addition of components in the processing of inks have been studied, with the most effective processing route using a fugitive solvent that probably facilitates uniform coverage of the particle surfaces by the dispersant molecules. Modeling of the rheological profiles of inks indicates that the use of a dispersant decreases the depth of the primary minimum in the interparticle potential by a factor of 3. Demonstrated advantages of the use of a dispersant in PZT thick-film inks include improved microstructural homogeneity in the green body and the ability to formulate printable inks with higher solids loadings. No adverse effects of the dispersant upon the dielectric and piezoelectric properties of bulk PZT samples are found following burnout and sintering.     

Formation of Lead Zirconate Titanate Powders by Spray Pyrolysis

Twin-fluid atomization spray pyrolysis (SP) has been investigated for the production of lead zirconate titanate (PZT) powders, using aqueous solutions of lead acetate and zirconium and titanium alkoxide precursor reagents. The particle size distribution of the PZT powder showed a d ₅₀ value of 0.3 μm, but with a small fraction of relatively large particles, several micrometers in size. Most particles were spherical but many of the largest particles, in the size range ca. 1–5 μm, were irregular. It was demonstrated that the morphology of the final PZT powder was controlled by decomposition processes occurring during the initial drying stages, at ≤200°C. A pyrochlore or fluorite-type intermediate crystalline phase was present in the final powders, but when the maximum reactor temperature was raised, and/or when the levels of excess lead in the starting solutions were increased, the proportion of the desired perovskite phase increased. However, at the highest process temperatures studied, ∼900°C, small crystallites of another phase formed on the surface of the PZT particles; these were probably lead oxide carbonate particles. Overall, a starting solution composition containing around 5 mol% excess Pb, and a maximum reactor temperature of 800°C, were selected as offering the most suitable conditions for producing PZT (52/48) powder, with minimal secondary phases(s). Preliminary densification studies showed that the powders could be sintered at 1150°–1200°C to give pellets of 95%–96% theoretical density.     

Strong Electromechanical Response in Lead Zirconate Titanate Metamaterials

As a class of technically important functional materials, Pb(Zr,Ti)O₃ (PZT)‐based materials have been widely used in different types of piezoelectric devices. These materials are also ferroelectrics, and the materials lose their piezoelectric properties above the Curie temperature, a drawback limiting applications of the materials at high temperatures. Designing piezoelectric metamaterials by exploiting the flexoelectricity of the PZT‐based materials is a possible solution to this issue. In this work, PZT‐based piezoelectric metamaterials can be designed by applying an asymmetric chemical reduction to PZT ceramics to produce a curvature. The reduced PZT ceramic wafers exhibit a high apparent piezoelectric response (>2900 pC/N), which can be sustained after a heat treatment at 550°C for 5 h, which is more than 250°C above their Curie temperature. A substantial piezoelectric response can also be directly measured well above the Curie temperature. The mechanism underlying this very high apparent piezoelectric response with high‐temperature stability is investigated. The experimental results suggest that the electromechanical response mainly originates from the flexoelectric effect when the reduction‐induced curvature is bent under stress. The formation of the curvature also causes strain gradient‐induced poling of the reduced materials, resulting in a weak piezoelectric response from partly oriented polarization, which partly contributes to the observed response.     

Effect of Lead Zirconate Titanate Seeds on PtxPb Formation during the Pyrolysis of Lead Zirconate Titanate Thin Films

Lead zirconate titanate (PZT) thin films were prepared on platinized silicon substrates by dip-coating using a modified diol-based sol–gel route without and with up to 5 mol% PZT nanometric seeds dispersed in the precursor sol. A metastable intermetallic Pt _x Pb phase formed at the early stages of heat treatment. XRD, TEM, and RBS revealed that the thickness and stoichiometry of the Pt _x Pb layer varied with the concentration of seeds and heat treatment of the films. The relation of the Pt _x Pb layer to the final crystalline texture of the PZT thin films is reported and discussed.     

Effects of Octahedral Tilting on the Piezoelectric Properties of Strontium/Barium/Niobium-Doped Soft Lead Zirconate Titanate Ceramics

(Pb_1−x−ySr_xBa_y)(Zr_0.976−zTi_zNb_0.024)O₃ solid solutions have been investigated to understand the relationship between structural changes caused by isovalent strontium and barium substitution on the A-site and dielectric and piezoelectric properties. As strontium and barium were substituted for lead, the zirconium:titanium (Zr:Ti) ratio was modified so that all compositions had an optimized piezoelectric coefficient (d₃₃). The value of d₃₃ was at a maximum in the tetragonal phase near, but not at, the morphotropic-phase boundary (MPB). The real MPB was taken as the Zr:Ti ratio at which X-ray diffraction patterns appeared either pseudocubic or a mixture of rhombohedral and tetragonal. As strontium content increased, optimized d₃₃ also increased from 410 pC/N (x= 0) to 640 pC/N (x= 0.12), commensurate with a decrease in the paraelectric-to-ferroelectric phase transition temperature (T_C) from 350°C (x= 0) to 175°C (x= 0.12). However, for ceramics where x > 0.12, optimized d₃₃ decreased even though the phase-transition temperature was ∼150°C. Low strontium concentration ceramics (x= 0–0.08) contained 80 nm ferrroelectric domains typical of PZT, but high strontium concentration ceramics (x= 0.12–0.16) contained fine-scale domains (20 nm) in some regions of the microstructure. In addition, [110] pseudocubic electron diffraction patterns revealed superlattice reflections at 1/2{hkl} positions associated with rotations of the octahedra in antiphase. Co-doping ceramics with strontium (x= 0.06) and barium (y= 0.06) resulted in the disappearance of the 1/2{hkl} reflections. Optimized d₃₃ (∼520 pC/N, T_C∼ 205°C) for this composition was similar to that of ceramics where x= 0.08, y= 0, which had a T_C of ∼250°C.     

Properties of Lead Zirconate Titanate Thin Films Prepared Using a Triol Sol–Gel Route

Microstructure and phase development during the thermal decomposition of sol–gel precursor coatings of PbZr_0.53Ti_0.47O₃ on platinized silicon substrates have been investigated for a triol sol–gel route. The single-layer, 0.4 μm PZT films were heated from below the substrate, over the temperature range 350–600°C, using a calibrated hot plate. The first crystalline phase to appear was a PbPt₃ intermetallic phase at the Pt/PZT interface. Although perovskite PZT formed at ca. 500°C, heating at higher temperatures, for example 550°C for 30 min, was required to develop ferroelectric hysteresis loops. However, the rather low value of remanent polarization, P _r= 11 μC·cm⁻², was consistent with incomplete crystallization at 550°C. The values of remanent polarization increased with increasing processing temperatures, reaching 21 μC·cm⁻² for samples heated at 600°C, with a corresponding E _c value of 57 kV·cm⁻¹. Distinctive spherical precipitates up to ca. 50 nm in size have been identified by TEM in the lower portions of otherwise amorphous coatings, after heating at around 350–400°C. Although their precise composition could not be identified, they were mostly Pb-rich, and it is speculated that they form due to reduction of some of the lead(II) acetate starting reagent, to atomic Pb during the early stages of thermal decomposition of the organic components of the gel; it is possible that subsequent reactions occur to form lead oxides or carbonates. High levels of porosity were present in many of the fully crystallized films. The possible reasons for this are discussed.     

Fabrication of NiO Nanoparticle-Coated Lead Zirconate Titanate Powders by the Heterogeneous Precipitation Method

NiO nanoparticle-coated lead zirconate titanate (PZT) powders are successfully fabricated by the heterogeneous precipitation method using PZT, Ni(NO₃)₂·6H₂O, and NH₄HCO₃ as the starting materials. The amorphous NiCO₃·2Ni(OH)₂·2H₂O are uniformly coated on the surface of PZT particles. XRD analysis and the selected-area diffraction (SAD) pattern indicate that the amorphous coating layer is crystallized to NiO after being calcined at 400°C for 2 h. TEM images show that the NiO particles of ∼8 nm are spherical and weakly agglomerated. The thickness of the nanocrystalline NiO coating layer on the surface of PZT particle is ∼30 nm.     

Phase Stability and Ferroelectric Properties of Lead Strontium Zirconate Titanate Ceramics

The effect of compositional modifications on the field-induced phase-transition behavior and dielectric properties of strontium-doped lead zirconate titanate (PZT) ceramics was studied. PZT compositions with different strontium and titanium contents, within the general formula Pb_{1– x} Sr _x (Zr_{1– y} Ti _y )O₃ and located in the tetragonal antiferroelectric (AFE) and rhombohedral ferroelectric (FE) phase fields were prepared by tape casting and sintering. X-ray diffraction and polarization measurements were used to locate compositions suitable for investigation of the field-induced AFE–FE phase transition. The results indicated that a higher Sr²⁺ content decreased the polarization and hysteresis and increased the switching field; a lower Ti⁴⁺ content decreased the polarization and increased the switching field and hysteresis. A high room-temperature dielectric constant was obtained for compositions near the phase boundary. These results suggest that a combination of both A -site and B -site modifications can be used to tailor ferroelectric properties, such as the switching field and hysteresis, of these strontium-doped PZTs displaying a field-induced AFE–FE phase transition.     

R-Curve for a Lead Zirconate Titanate Ceramic Obtained from Tensile Strength Tests with Knoop-Damaged Specimens

A procedure was used that made it possible to determine the R -curve for piezoelectric ceramics from tensile strength tests conducted with Knoop-damaged specimens. The resulting crack-tip toughness K _I0 was 0.6 MPa·m^1/2, and the R -curve starting from this value increased to 1.4 MPa·m^1/2 within a 0.7 mm crack extension.     

Novel Synthesis Route to Make Nanocrystalline Lead Zirconate Titanate Powder

The present research describes synthesis of perovskite lead zirconate titanate (PZT) nanocrystalline mesoporous powders from the aqueous solutions of Pb²⁺, Zr⁴⁺, and Ti⁴⁺ metal ions using sucrose as a template material. Sucrose retains the metal ions in solution through complex formation. Dehydration and thermal decomposition of the metal ion–sucrose mass produces a large amount of gas, which helps to create porosity and high surface area in the final products. The particle size of the synthesized powder is between 50 and 60 nm, with a average specific surface area between 20 and 25 m²/g. The surface area increases as the amount of sucrose increases. Nanocrystalline PZT powder with high surface area can be useful for low-temperature sintering.     

Differences in Tensile and Bending Strength for Knoop-Cracked Lead Zirconate Titanate Specimens

The strength of piezoelectric ceramics differs greatly in tension and bending tests. This effect, which is known to occur for specimens with a natural flaw population, also occurs in tests that involve Knoop-cracked specimens. In such samples, the linear-elastically computed bending strength is ∼35% higher than the tensile strength. Computation of the actual stress distribution in the bending bars has shown that these differences are predominantly caused by the nonlinearity and nonsymmetry of the deformation behavior.     

Structural and Property Evolution of Aqueous-Based Lead Zirconate Titanate Tape-Cast Layers

We have developed aqueous suspensions of lead zirconate titanate (PZT) and an acrylic latex emulsion binder for tape casting. Rheological measurements were conducted to optimize their flow behavior at high solids volume fraction (φ_solids). Concentrated suspensions (φ_solids > 0.45) were tape cast onto a silicone-coated mylar carrier film, and the effect of cellulose (a viscosifier) and surfactant additions on wetting behavior was studied. Drying stress measurements were performed on tape-cast layers using a substrate deflection technique. The initial period of stress rise was analogous to that observed for binder-free ceramic films, whereas the stress decay was influenced by latex coalescence. Tape-cast layers exhibited a constant PZT volume fraction of 0.49 and uniform binder distribution independent of the PZT/latex volume ratio. The dielectric and piezoelectric properties of sintered multilayer samples were comparable to those obtained for bulk, isopressed samples. Our work provides guidelines for developing aqueous formulations for tape casting complex electroceramic oxide layers.     

Processing and Sol Chemistry of a Triol-Based Sol–Gel Route for Preparing Lead Zirconate Titanate Thin Films

A triol-based sol–gel system has been developed for the fabrication of thin films of lead zirconate titanate (PZT). Starting reagents were lead acetate, zirconium and titanium isopropoxides, acetylacetone, and 1,1,1-tris(hydroxymethyl)ethane (THOME), with 2-methoxyethanol (MOE) being used to dilute the sols for spin coating purposes. Preliminary characterization by NMR spectroscopy suggested that the gels consisted of the metal ions and bound THOME, acetylacetonate, and acetate residues, with some possible M–O–M bridges. Uncracked 0.4 μm single-layer PZT films of nominal composition PbZr_0.53Ti_0.47O₃ were prepared on platinized substrates. Dielectric and ferroelectric properties were determined for samples made from sols containing 10 and 15 mol% excess lead acetate. Improved values were obtained for samples made from sols containing the higher excess; these exhibited a remanent polarization of 34 μC·cm⁻¹, a coercive field of 54 kV·cm⁻¹, and a relative permittivity of 1000.     

Directed Colloidal Assembly of Linear and Annular Lead Zirconate Titanate Arrays

Lead zirconate titanate (PZT) arrays for ultrasonic sensing applications in the 2–30-MHz frequency range were fabricated by robocasting, a directed colloidal assembly technique. Both linear and annular arrays were produced by robotically depositing a concentrated PZT gel-based ink to create high-aspect-ratio PZT elements (thickness ∼ 130 μm and height ∼1–2 mm) of varying pitch (∼250–410 μm). The arrays were densified and infiltrated with an epoxy resin to fabricate PZT–polymer composites with 2–2 connectivity. Their dielectric and piezoelectric constants were measured and compared with values obtained for bulk PZT and those predicted theoretically.     

Lead Zirconate Titanate Thin Films by Aerosol Plasma Deposition: Microstructure Analysis

Lead zirconate titanate (Pb(Zr,Ti)O₃, PZT) thin films were grown on silicon 〈100〉 substrate by aerosol plasma deposition (APD) using solid-state-reacted powder containing donor oxide Nb₂O₅ when keeping the substrate at room temperature and 200°C. Crystalline phases of the deposited films have been analyzed via X-ray diffractometry (XRD), and microstructure via scanning and transmission electron microscopy (SEM and TEM). Cross-sectional TEM revealed that the microstructure comprised several layers including the deposited PZT film and the platinum-electrode-and-titanium-buffered layers on SiO₂–Si substrate. The Pt-electrode layer contained (111)_Pt twinned columnar grains with a slight misorientation and forming low-angle grain boundaries among them. The PZT layer contained randomly oriented grains embedded in an amorphous matrix. Some of the PZT grains, oriented with the zone axis Z = [[Twomacr]11]_PZT parallel to Z = [111]_Pt, were grown epitaxially on the Pt layer by sharing the (111)_PZT plane with the (111)_Pt twinned columnar Pt crystals. However, the existence of such an orientation relationship was confined to several nanosize grains at and near the PZT-Pt interface, and no gross film texture has been developed. An amorphous grain boundary phase, generated by pressure-induced amorphisation (PIA) in the solid state, was identified by high-resolution imaging. Its presence is taken to account for the densification of the PZT thin films via a sintering mechanism involving an amorphous phase on deposition at 25° and 200°C.