Ferroelectric ceramics were born in the early 1940s with the discovery of the phenomenon of ferroelectricity as the source of the unusually high dielectric constant in ceramic barium titanate capacitors. Since that time, they have been the heart and soul of several multibillion dollar industries, ranging from high-dielectric-constant capacitors to later developments in piezoelectric transducers, positive temperature coefficient devices, and electrooptic light valves. Materials based on two compositional systems, barium titanate and lead zirconate titanate, have dominated the field throughout their history. The more recent developments in the field of ferroelectric ceramics, such as medical ultrasonic composites, high-displacement piezoelectric actuators (Moonies, RAINBOWS), photostrictors, and thin and thick films for piezoelectric and integrated-circuit applications have served to keep the industry young amidst its growing maturity. Various ceramic formulations, their form (bulk, films), fabrication, function (properties), and future are described in relation to their ferroelectric nature and specific areas of application.

/pdf/ferroelectric-ceramics-history-and-technology-40j9enkrwl.pdf

Ferroelectric ceramics : History and technology

We have examined the static and dynamic electromechanical responses of PZT‐brass (piezoelectric‐nonpiezoelectric) plate unimorphs of various brass/PZT thickness ratios. The study was performed both experimentally and theoretically. The static measurements showed that, given a PZT layer thickness, there exists a brass/PZT thickness ratio that gives the unimorph the highest static displacement under an applied field. The effects of geometric shape and external loading on the displacement of the unimorphs were also examined. The dynamic measurements showed that, given a PZT layer thickness, the bending-mode resonance frequencies increase with an increasing brass/PZT thickness ratio. These results were in good agreement with the theoretical predictions that were obtained with the plate geometry.

/pdf/electromechanical-behavior-of-pzt-brass-unimorphs-bvrovzy1lj.pdf

Electromechanical Behavior of PZT-Brass Unimorphs

Piezoelectric generators enable maintenance-free power supply for integrated electronics in smart system applications. The majority of publications consider the aspect of power transfer electronics; however, the influence of the transducer materials was rarely described. Recently, material characteristics received increased attention from the ceramics community. We set the focus of the present paper to commercially available piezoelectric ceramics. Different figures of merit are derived from system analysis using electromechanical modeling. They allow for the description of typical load scenarios and commercial piezoceramics. Derived rules are expected to be helpful for guiding ceramic engineers and system designers to succeed in improved generator solutions.

A Survey on Piezoelectric Ceramics for Generator Applications

A piezoelectric/electrostrictive RAINBOW actuator is a monolithic bending device consisting of an electromechanically active layer and a reduced passive layer formed in a high-temperature reduction treatment. When the piezoelectric or electrostrictive layer is driven under an electric field or when the environmental temperature changes, bending deflection is produced because of the constraint of the reduced inactive layer or because of the thermal expansion coefficient difference of the two layers. In this study, general analytical expressions relating tip deflection, blocking force, and equivalent moment with an applied electric field and temperature change are derived for a cantilevered RAINBOW actuator. It is shown that optimal actuator performance can be achieved in the RAINBOW actuator by choosing a suitable thickness ratio of the reduced layer to the PZT layer. A series of RAINBOW cantilever actuators have been experimentally prepared from high-density, soft, lead zirconate titanate (PZT) ceramics. Different reduction layer thickness is obtained by adjusting the processing parameters, such as reduction temperature and time. The measured results on tip deflection and blocking force agree well with theoretical prediction under a weak electric field. However, when a high driving electric field is used, deviation is observed, which can be attributed to a nonlinear piezoelectric response and a nonlinear elastic behavior associated with soft PZT materials under high driving electric fields.

Tip Deflection and Blocking Force of Soft PZT-Based Cantilever RAINBOW Actuators

Recent developments in the technology of ferroelectric, piezoelectric, electrostrictive and antiferroelectric ceramic actuators have clearly demonstrated that the materials required for future applications such as positioners, levelers, pumps, vibration-free structures and variable-focus elements will need to be more sophisticated (multifunctional and smart), more economical and possess a higher degree of performance than presently available. One recently developed method for producing considerably higher- than-normal displacement in these materials is known as the RAINBOW (Reduced and INternally Biased Oxide Wafer) technology. This acronym denotes the basic active structure of the Rainbow device which is produced by a special high temperature chemical reduction process. In its most basic sense, a Rainbow can be considered to be a pre-stressed, monolithic, axial-mode bender; however, because of its unique dome or saddle-shaped configuration, it is able to produce much higher displacements (up to several mm depending on size) and sustain moderate loads (up to 10 kg depending on thickness) than normal benders such as unimorphs and bimorphs. The technology of producing and characterizing such Rainbows as well as methods for increasing their utility by means of stacked actuators for increased linear displacement and matrix arrays for enhanced coverage in wide-area applications such as smart skins, autoleveling structures and deformable coatings are described.

Rainbow actuators and sensors: a new smart technology

Reduced and internally biased oxide wafer (RAINBOW) actuators are fabricated by a controlled reduction of Pb(Zr, Ti)O3-based piezoelectric material. The reduction process results in a conductive layer composed of an interconnected metallic lead phase and refractory oxides (ZrTiO4, ZrO2, La2O3, etc.). The nature of the reduction is discovered to be the result of a complex volume change leading to a nanoscale interconnected metallic structure. The distribution of phases within the cermet vary within the thickness of the wafer. Within the piezoelectric ceramic phase, the reduction process modifies the grain-boundary structure to give two distinct types of fracture: transgranular and intergranular. The complexed microstructures of the RAINBOW actuator materials are discussed in relation to their dielectric and piezoelectric properties.

Structural-property relations in a reduced and internally biased oxide wafer (RAINBOW) actuator material

The piezoelectric resonance behavior of end-clamped bimorph structures made from the rainbow monolithic ceramic have been evaluated. Thickness, width, width flexure, and length bending modes have been identified and measured. Using a very crude model in which the cermet component of the rainbow is assumed to have the same density × elasticity product as the bulk, surprisingly good agreement is obtained between observed and calculated frequency behavior. By appropriate processing it is possible to delaminate the bimorph, and work is now in progress to measure the properties of the two separate phases so that a proper composite resonator model may be developed.

Catherine Elissalde

Papers

Structural-property relations in a reduced and internally biased oxide wafer (RAINBOW) actuator material

Dynamic Characteristics of Rainbow Ceramics