Michael R. Winter

Barium titanate nanocomposite capacitor FY09 year end report.

This late start RTBF project started the development of barium titanate (BTO)/glass nanocomposite capacitors for future and emerging energy storage applications. The long term goal of this work is to decrease the size, weight, and cost of ceramic capacitors while increasing their reliability. Ceramic-based nanocomposites have the potential to yield materials with enhanced permittivity, breakdown strength (BDS), and reduced strain, which can increase the energy density of capacitors and increase their shot life. Composites of BTO in glass will limit grain growth during device fabrication (preserving nanoparticle grain size and enhanced properties), resulting in devices with improved density, permittivity, BDS, and shot life. BTO will eliminate the issues associated with Pb toxicity and volatility as well as the variation in energy storage vs. temperature of PZT based devices. During the last six months of FY09 this work focused on developing syntheses for BTO nanoparticles and firing profiles for sintering BTO/glass composite capacitors.

Ceramic processing of template-induced microstructure textured ceramics PI008

The target of this work is to develop an advanced manufacturing process that results in a bulk polycrystalline electroceramic component through a texture induced forming method. The technique produces a bulk ceramic component that exhibits enhanced macroscopic properties when compared to a traditional electroceramic material that has electrically induced ferroelectric texture or crystallographic texture. Templated texturing can involve the ¿laying down¿ of seed crystals with planar morphology to induce preferential grain growth within a pre-designed orientation of the bulk ceramic. Through well-controlled slurry processing of ceramic powders and the addition of templated crystals it is possible to induce this preferential grain orientation for sintered ceramics. This work will present the results of a comparison between three separate advanced ceramic forming techniques; tape casting, thick film screen printing, and extrusion, examining the degree of microstructure texture developed by these methods.

Textured processing, reactive templated grain growth, and electrical property relationships for sodium bismuth titanate PI015

The investigation of lead-free piezoelectric ceramic compositions has recently gained an increased level of interest due to the efforts to reduce lead based components. The most widely used piezoelectric/ferroelectric ceramic material today, including specialized ceramics for military applications (ex. sonar), consists of PbTiO3-PbZrO3 (i.e. PZT-system). It has become imperative to integrate a processing strategy with a lead-free ferroelectric material capable of competing with or surpassing the properties of lead-based compositions. This work examines the development of optimal processing parameters through texturing and reactive templated grain growth to selectively engineer a polycrystalline ceramic microstructure. It presents how these parameters can affect the electro-mechanical properties for a sodium bismuth titanate based composition. The final properties for all ceramic materials are highly influenced by the processing steps and forming techniques used to construct the bulk ceramic component. Texturally modified ceramic compositions have recently exhibited enhanced properties that, depending on the system, match and even surpass those of an optimum modified lead-based composition. In this work we report on the development and use of a texture induced forming process combined with reactive templated grain growth to produce grain-oriented polycrystalline bulk ceramics. Thermal analysis, x-ray diffraction characterization, microstructure stereology and the dielectric and electromechanical performance will be presented. A processing space has been characterized and mapped in order to drive towards achieving maximized electrical performance for this lead-free system.

Characterization of the electro-mechanical behavior of zirconia-rich PZT ceramics

Lead zirconate titanate (PZT) ceramics near the morphotropic phase boundary have been the backbone materials for piezoelectric applications for more than 50 years. The electro-mechanical responses for these materials have been well studied. In this study, we investigated the electro-mechanical behavior of two zirconia-rich PZT compositions, with and without tin (Sn) modification. These materials, close to the antiferroelectric phase region, have been used for power supply and actuator applications due to their unique ferroelectric(FE)-antiferroelectric(AFE) phase transformation behavior. However, limited information is available characterizing their electromechanical responses, especially outside of room temperature. In this work, we present the electromechanical properties of these compositions as a function of temperature. Special attention has been placed on the electromechanical responses near the FE-FE phase transformation.

PI017 - thick film texturing to enhance the properties of lead-free ferroelectric materials

Increasing concern surrounding the use of lead in consumer products has stimulated research to identify candidates to replace lead-based materials used in many commercial applications. To be integrated into commercial products; however, a lead-free replacement must be fabricated using common industrial techniques while maintaining dielectric properties equivalent to the current lead-based systems. Texturing has been shown to dramatically enhance the dielectric properties of lead-free materials such that several potential systems are now being considered as replacements for the current lead-based materials. In this work, a large degree of texturing has been introduced to bismuth titanium oxide bulk samples through the process of screen printing large, plate-like seeds in a matrix of equi-axial powder. The degree of texturing achieved gives rise to a high probability of excellent dielectric properties, making textured bismuth titanate a viable replacement for commercial lead-based dielectrics.