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.     

Piezoelectric Multilayer Ceramic/Polymer Composite Transducer with 2–2 Connectivity

A multilayer piezoelectric ceramic/polymer composite with 2–2 connectivity was fabricated by thermoplastic green machining after co-extrusion. The multilayer ceramic body was composed of piezoelectrically active lead zirconate titanate (PZN)–lead zinc niobate (PZN)-lead zirconate titanate (PZT) layers and electrically conducting PZN–PZT/Ag layers. After co-extruding the thermoplastic body, which consisted of five piezoelectric layers interspersed with four conducting layers, it was computer numeric-controlled machined to create periodic channels within it. Following binder burnout and sintering, an 18 vol% array of 190 μm thin PZT slabs with a channel size of 880 μm was fabricated. The channels were filled with epoxy in order to fabricate a PZN–PZT/epoxy composite with 2–2 connectivity. The piezoelectric coefficient (effective d ₃₃) and hydrostatic figure of merit ( d _h× g _h) of the PZN–PZT/epoxy composite were 1200 pC/N and 20 130 × 10⁻¹⁵ m²/N, respectively. These excellent piezoelectric characteristics as well as the relatively simple fabrication procedure will contribute in widening the application range of the piezoelectric transducers.     

Thermoplastic Green Machining for the Fabrication of a Piezoelectric Ceramic/Polymer Composite with 2-2 Connectivity

A piezoelectric ceramic/polymer composite with 2-2 connectivity was fabricated by thermoplastic green machining. A thermoplastic body, consisting of 60 vol% lead zirconate titanate ceramic particles (PZT) and 40 vol% thermoplastic binders, was computer numeric controlled-machined, creating periodic channels in the green PZT body. Following thermal treatment (binder burnout and sintering), a 25 vol% array of 147 μm thin PZT slabs with an aspect ratio of seven separated by 442 μm channels was fabricated. The channels were infiltrated with epoxy resin, in order to fabricate the PZT/epoxy composite with 2-2 connectivity. This novel process was evaluated in terms of the machinability and sinterability of the thermoplastic PZT compound. Also, the electromechanical properties of the PZT/epoxy composite were measured.     

Lead Zirconate Titanate Fiber/Polymer Composites Prepared by a Replication Process

The woven replication process was used to fabricate lead zirconate titanate (PZT)/polymer composites with 1–3, 2–3, and 3–3 connectivities by starting with novoloid-derived carbon fiber, woven fabric, and nonwoven felt templates, respectively. Activated carbon-fiber template material was impregnated with PZT by soaking it in a solution containing stoichiometric amounts of dissolved lead, zirconium, titanium, and niobium ions. Heat treatment burned out the carbon, leaving a PZT replica with the same form as the template material. Replicas were sintered in a controlled atmosphere and backfilled with an epoxy polymer to form final composites. This method, which is believed to be adaptable for mass production, is capable of producing composites with extremely fine microstructures. Woven composite samples have fiber tow diameters of 200 to 250 μm and spacings between tows of about 150 to 250 μm. Average d ₃₃= 90 pC/N, g ₃₃= 211 mV · m/N, and d_hg_h hydrophone figure of merit of 2100 × 10⁻¹⁵ m²/N values are reported for woven PZT/polymer composites.     

Sintering and Piezoelectric Properties of Co-Fired Lead Zirconate Titanate/Ag Composites

Lead zirconate titanate (PZT) ceramics were co-fired with pure Ag powders at 1200°C for 1 h, and the ferroelectric and piezoelectric properties of the resultant PZT/Ag composites were evaluated, aimed at potential applications in functionally graded piezoelectric actuators with enhanced mechanical reliabilities. In the range of 1–15 vol% Ag concentration, pure Ag powder remained as the second phase in the composites, and a small quantity of Ag entered into the crystal lattice of PZT and slightly increased the lattice constants of a and c . The Ag powders were found to aggregate together and grow to larger particles in the composites. The ceramic grains grew from an initial size of 1.5 μm for monolithic PZT to 2.5 μm for the PZT/Ag composites, and the grain size was almost the same for various Ag concentrations. It was found that the ferroelectric and piezoelectric properties decreased when Ag was added to PZT. In the range of 1–15 vol% Ag concentration, the remanent polarization P _r decreased from 38 to 27 μC/cm², the piezoelectric constant d ₃₃ decreased from 394 to 105 pC/N, and the planar electromechanical coupling factor k _p decreased from 0.69 to 0.15, respectively. These piezoelectric properties of the present PZT/Ag composites were compared with the results reported for PZT/Pt composites, and discussed in relation to microstructural features.     

Properties of 0–3 Lead Zirconate Titanate–Polymer Composites Prepared in a Centrifuge

The purpose of this work was to present the electrical and piezoelectric properties of the 0-3 piezoceramic–polymer composites prepared by spinning the lead zirconate titanate (PZT) powders with polyester resin in a centrifuge. PZT powders with average sizes of 55 and 160 μm were used and mixed in the resin with different volumetric percentages. The dielectric and piezoelectric properties such as permittivity, loss angle, electromechanical coupling factor, and piezoelectric coefficient were measured. The mechanical quality factor was calculated. The acoustic impedance was accessed by the echo-shift method. The results were analyzed and fit to mechanical models. Distribution of the ceramic particles in the polyester-resin phase was examined by scanning electron microscopy. Smaller-ceramic-particle composites seemed to form denser samples. Most of the properties showed linearly varying as the volumetric percentage of the ceramic phase. The fabrication using the centrifuging techniques resulted in more homogeneity of the ceramic and polymer phases, and the fabricated samples could be loaded up to 65% or more with the ceramic powders.     

Fatigue-Free Lead Zirconate Titanate (Pb(Zr,Ti)O3)-Based Capacitors Co-modified by Lanthanum and Lithium for Nonvolatile Memories

Pb_0.98(La_{1− x} Li _x )_0.02(Zr_0.55Ti_0.45)O₃(PLLZT with 0.1 ≤ x ≤ 0.7) thin films were sol-gel-grown on Pt(111)/Ti/SiO₂/Si substrates, employing a thin lead zirconate titanate (PZT) template layer. Films annealed at >550°C showed a highly (111)-oriented preferential growth. Typical values of the switchable remanent polarization (2 P _r) and the coercive field ( E _c) of the PLLZT/PZT/Pt film capacitor for x = 0.3 were 50 μC/cm² and 39 kV/cm, respectively, at 5 V. All the PLLZT/PZT/Pt capacitors (for 0.1 ≤ x ≤ 0.7) exhibited fatigue-free behavior up to 6.5 × 10¹⁰ switching cycles, a quite stable charge retention profile with time, and high 2 P _rvalues, all which assure their suitability for nonvolatile ferroelectric memories.     

Processing of 1-3 Piezoelectric Ceramic/Polymer Composites

Several methods of forming fine-scale 1–3 piezoelectric ceramic/polymer composites for possible transducer applications were demonstrated. These methods include tape casting, honeycomb dicing, and ceramic fiber weaving. In the tape casting technique, laminated structures were formed using thin PZT tapes. The tapes were stacked, with spacers separating the layers, and the stack embedded in polymer. Dicing the stack resulted in a composite with 1–3 connectivity. The thin tape technique can be used to develop composites with ceramic or polymer volume fraction gradients and multifunctional ceramics. Dicing of PZT honeycombs yields 1–3 composites with uniquely shaped rods. Shapes included +, T, and L. In the ceramic fiber weaving technique, green PZT fibers were woven through a PZT honeycomb support structure. The structure was fired to sinter the PZT fibers, and embedded with polymer to yield 1–3 composites. All 1–3 composites showed high and uniform piezoelectric coefficients across the electroded area.     

Fabrication of Perovskite-Based High-Value Integrated Capacitors by Chemical Solution Deposition

Projected trends for capacitors include increasing capacitance density and decreasing operating voltages, dielectric thickness and process cost. Advances in the fabrication and processing of barium strontium titanate (BST) and lead zirconate titanate (PZT)-based thin films are presented toward attaining these goals in next-generation high-value integrated capacitors. Increasing capacitance density has been demonstrated through the use of large-area electrodes, multilayer structures, and decreased dielectric layer thickness. Capacitance values as high as 10 μF were obtained in a single-layer, 10 cm² film, and layer thicknesses as small as 9 nm have been achieved using chemical solution deposition. Base metal integration results for BST and PZT films are discussed in terms of additional cost and volume reduction; such films have achieved capacitance densities as high as 1.5 μF/cm² and electric fields of 25 V/μm.     

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.     

Processing of Piezocomposites by Fused Deposition Technique

Piezoelectric ceramic/polymer composites were made by a fused deposition (FD) technique, which is a solid-freeform fabrication (or layered manufacturing) technique where three-dimensional (3-D) objects are built layer by layer from a computer-aided design (CAD) file on a computer-controlled fixtureless platform. Indirect and direct FD methods were used to fabricate lead zirconate titanate (PZT)/polymer composites. For the indirect method, a CAD file for the negative image of the final part was created. A polymer mold was made via FD using a thermoplastic filament, and composite formation was completed via a lost mold technique. In the direct FD method, a thermoplastic polymeric filament that was filled with 50–55 vol% of PZT powder was used to form a positive image of the desired structure. Three-dimensional honeycomb ("3-D honeycomb") composites and "ladder" composites with 3-3 connectivity, which were formed via the FD technique, showed excellent electromechanical properties for transducer applications. In addition, the FD technique showed the ability to form composites with controlled phase periodicity, various volume fractions, and a variety of microstructures and macrostructures that are not possible with traditional composite-forming techniques.     

Fine‐Scaled Piezoelectric Ceramic/Polymer 2‐2 Composites for High‐Frequency Transducer

A novel technique was utilized to fabricate fine‐scaled piezoelectric ceramic/polymer 2‐2 composites for high‐frequency ultrasonic transducers. Lead zirconate titanate (PZT) was used as raw material. Tape‐casted acetylene black tapes were used to define kerfs after sintering. A one‐directional supporter was utilized to avoid distortion of PZT elements. PZT elements with 20 ± 2 μm width exhibited good consistency in longitudinal direction. A resonant method was utilized to evaluate the piezoelectric and dielectric properties of the composites. A 72‐μm‐thick composite with an aspect ratio of ~3.6 exhibited a k_t of 0.61 with satisfied piezoelectric and dielectric properties. A prototype high‐frequency ultrasonic transducer was fabricated and evaluated by an underwater pulse‐echo test. The center frequency was found to be 23.75 MHz, with ?6 dB bandwidth of 5.5 MHz.     

Novel Processing of 1-3 Piezoelectric Ceramic/Polymer Composites for Transducer Applications

Piezoelectric ceramic/polymer composites with 1-3 connectivity were made by weaving sized lead zirconate titanate (PZT) fiber bundles through a honeycomb support. Bundles comprised of fine-scale, 20-50 μm green fibers, made using the viscous suspension spinning process, were sized to increase their manageability. The sizing step comprised of soaking the green PZT fiber bundles in an aqueous solution of poly(vinyl alcohol), then pulling the wet fibers through a steel sizing die. Sizing resulted in dense and flexible fiber bundles, which facilitated composite construction and led to composites with increased volume fractons. Sintering, polymer embedding, and machining produced a composite exhibiting 1-3 connectivity. Composites with 10 vol% PZT yilded d ₃₃ values of 230 pC/N and a dielectric constant of 130.     

Poling of Lead Zirconate Titanate Ceramics and Flexible Piezoelectric Composites by the Corona Discharge Technique

In the conventional poling method, piezoelectric ceramics and composites are poled by applying a large dc voltage. Poling of composites having a polymer matrix with 0–3 connectivity is especially difficult because the electric field within the high-dielectricconstant grains is far smaller than in the low-dielectric-constant polymer matrix. Therefore, very large electric fields are required to pole these types of composites. However, large electric fields often cause dielectric breakdown of the samples. In this study for improved poling, the corona discharge technique was used to pole piezoelectric ceramics, fired PZT composites, and 0.5PbTiO₃· 0.5BiFeO₃ 0–3 polymer composites. An experimental setup for corona poling is described. The dielectric and piezoelectric properties of materials poled by the corona discharge technique were comparable to those obtained with the conventional poling method.     

Development of Fine Scale PZT Ceramic Fiber/Polymer Shell Composite Transducers

The relic processing technique was used to fabricate fine-scale piezoelectric lead zirconate titanate (PZT) ceramic fiber/polymer shell composites. In this technique sacrificial activated carbon fabrics were soaked in a PZT precursor solution, dried, and heat treated to form piezoceramic relics. Relics were embedded with polymer, which was allowed to cure, and the resulting composites were polished, electroded, and poled. Different facets of the composite- forming process were examined: structural modifications, soaking, firing, and polymer impregnation. The physical and electromechanical properties of the unique resulting composite were evaluated. Optimized PZT shell composites with 39 vol% ceramic exhibited the following property values: K ε200, tan δε5.5%, d ₃₃ε290 pC/N, d _hε100 pC/N, d _h g _hε6000 ± 10^-15 m²N, k _pε0.19, and k _tε0.28.     

PO2 Dependence of the Diffuse-Phase Transition in Base Metal Capacitor Dielectrics

The diffuse-phase transition in BaTiO₃-based dielectrics for capacitor applications has been studied with respect to its dependence on oxygen partial pressure during sintering. Understanding the mobility of this transition is critical in developing next generation dielectrics for ultra thin (≤1 μm) applications while maintaining the appropriate temperature stability and insulation resistance. Historically, a heterogeneous core/shell microstructure was developed to maintain temperature stability. However, in fired grains of ≤250 nm (required for layers ≤1 μm) a well-defined core/shell structure is very difficult to establish. The results from this study demonstrate that careful control of the diffuse-phase transition addresses some of these problems.     

In-Plane Polarized 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 Thin Films

Ferroelectric 0.7Pb(Mg_1/3Nb_2/3)O₃–0.3PbTiO₃ (PMN-PT) thin films were deposited on ZrO₂/SiO₂/silicon substrates using a chemical-solution-deposition method. Using a thin PZT film as a seed layer for the PMN-PT films, phase-pure perovskite PMN-PT could be obtained via rapid thermal annealing at 750°C for 60 s. The electrical properties of in-plane polarized thin films were characterized using interdigitated electrode arrays on the film surface. Ferroelectric hysteresis loops are observed with much larger remanent polarizations (∼24 μC/cm²) than for through-the-thickness polarized PMN-PT thin films (10–12 μC/cm²) deposited on Pt/Ti/Si substrates. For a finger spacing of 20 μm, the piezoelectric voltage sensitivity of in–plane polarized PMN-PT thin films was ∼20 times higher than that of through-the-thickness polarized PMN-PT thin films.     

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.     

Silicon Carbide Platelet/Alumina Composites: II, Mechanical Properties

The mechanical properties, i.e., Young's modulus, fracture toughness, and flexural strength, of SiC-platelet/Al₂O₃ composites with two different platelet sizes were studied. Both Young's modulus and the fracture toughness of composites using small platelets (12 μm) increased with increasing SiC volume fraction. Maximum values for toughness and Young's modulus of 7.1 MPa·m^1/2 and 421 GPa were obtained for composites containing 30 vol% platelets. Composites fabricated using larger platelets (24 μm), however, showed spontaneous microcracking at SiC volume fractions of ≤0.15. The presence of microcracks decreased Young's modulus and the fracture toughness substantially. Two types of radial microcracks were identified by optical microscopy and found to be consistent with a residual stress analysis. Anisotropy in fracture toughness was identified with a crack length indentation technique. Cracks propagating in a plane parallel to platelet faces experienced the least resistance, which was the the lowest toughness plane in platelet composites with preferred orientation. Enhanced fracture toughness was found in the plane parallel to the hot-pressing direction, but no anisotropy in toughness was observed in this plane. The flexural strength of alumina showed a decrease from 610 to 480 MPa for a 30 vol% composite and was attributed to the presence of the platelets.     

Relic Processing of Fine-Scale, Large-Area Piezoelectric Ceramic Fiber/Polymer Composites

Fine-scale, large-area lead zirconate titanate (PZT) ceramic fiber/polymer composites were developed using the relic method. Carbon fabrics were used as a starting template material. These fabrics were soaked in PZT stock solution, stacked, and fired, removing the carbon and resulting in a relic structure identical to that of the original template. The relics were then sintered, backfilled with polymer, polished, and poled, resulting in a piezoelectric ceramic/polymer composite. The processing of the larger-area composites involved scaling up the procedure utilized in the fabrication of the smaller composites. The application of an optimum uniaxial pressure of 580 Pa to the stacks during firing was found to improve the piezoelectric properties and facilitate the increase in sample area. Scale-up to large area was achieved using two approaches: (1) the use of a larger template material, and (2) tiling smaller area relics together in an array configuration. The dielectric and piezoelectric properties of relic composites of 2.5 × 2.5 cm² area with ∼37 vol% PZT were K = 150 ± 8, d₃₃= 180 ± 11 pC/N, d_h= 85 ± 7 pC/N, and d _hg_h= 5525 × 10⁻¹⁵m²/N. The properties of large-area composites were comparable with those of small area.