Matthew M. Seabaugh

Templated Grain Growth of Textured Piezoelectric Ceramics

ABSTRACT Crystallographic texturing of polycrystalline ferroelectric ceramics offers a means of achieving significant enhancements in the piezoelectric response. Templated grain growth (TGG) enables the fabrication of textured ceramics with single crystal-like properties, as well as single crystals. In TGG, nucleation and growth of the desired crystal on aligned single crystal template particles results in an increased fraction of oriented material with heating. To facilitate alignment during forming, template particles must be anisometric in shape. To serve as the preferred sites for epitaxy and subsequent oriented growth of the matrix, the template particles need to be single crystal and chemically stable up to the growth temperature. Besides templating the growth process, the template particles may also serve as seed sites for phase formation of a reactive matrix. This process, referred to as Reactive TGG (RTGG), has been used to obtain highly oriented Pb(Mg1/3Nb2/3)O3-PbTiO3, Sr0.53Ba0.47Nb2O6, and (Na1/2Bi1/2)TiO3-BaTiO3. Highly oriented Bi4Ti3O12, Sr2Nb2O7, CaBi4Ti4O15, Pb(Mg1/3Nb2/3)O3-PbTiO3, Sr0.53Ba0.47Nb2O6 and (Na1/2Bi1/2)TiO3-BaTiO3 ceramics have been produced by TGG. The resulting ceramics show texture levels up to 90%, and significant enhancements in the piezoelectric properties relative to randomly oriented ceramics with comparable densities. For example, piezoelectric coefficients of textured piezoelectrics are from 2 to 3 times higher than polycrystalline ceramics and as high as 90% of the single crystal values. In textured PMN-PT, a low field (< 5 kV/cm) piezoelectric coefficient (d 33) of ∼1600 pC/N was obtained with > 0.3% strain (at 50 kV/cm). The high field dielectric and electromechanical properties of textured perovskites are more hysteretic than those of single crystals, probably as a result of clamping by the residual template particles, residual random grains, the presence of non-ferroelectric second phases, and a wide orientation distribution. Lateral clamping of one grain by another may also be an important factor in fiber-textured samples. Means to further improve the quality of texture and thus properties of textured piezoelectric ceramics by TGG are presented.

Fuel processing catalysts based on nanoscale ceria

Abstract The water-gas shift (WGS) reactor is a key component in fuel processors, but existing WGS catalysts are unsuitable for transportation applications, since the iron-chrome catalysts used at high temperatures are relatively inactive, and the copper-based catalysts used at low temperature tend to degrade under the severe conditions encountered in an automotive system. NexTech Materials has developed hydrothermal synthesis methods for dispersed suspensions of nanoscale ceria and ceria-zirconia, to give more active WGS catalyst, as well as more efficient and rugged catalyst packaging. The resulting WGS reactors based on ceramic monoliths loaded with Pt/ceria catalysts provide a technically viable and cost-effective option for automotive fuel processors.

Development of a Templated Grain Growth System for Texturing Piezoelectric Ceramics

High strain actuation can be obtained from crystallographically textured piezoelectric ceramics. Single crystal piezoelectrics demonstrate high strain because crystal orientation can be controlled - the perfect lattice simplifies crystal orientation. Single crystals actuate better than typical ceramics, but are expensive. Highly textured ceramics offer an alternative path to easily aligned crystals. The crystallites in textured ceramics are crystallographically oriented. Textured ceramics are expected to provide improved properties, with lower processing costs. NexTech Materials is developing textured piezoelectrics via Templated Grain Growth. In this process, anisotropic template particles are oriented in a fine matrix. During heat treatment, the templates grow, resulting in a textured polycrystal.

Oxide Protective Coatings for Solid Oxide Fuel Cell Interconnects

The oxidation kinetics of manganese cobalt (Mn,Co)3O4 spinel (MCO) coated AL 441-HP components have been determined by isothermal cyclic oxidation experiments over a range of temperatures from 800 to 1000 °C. Acceleration factors based on calculated parabolic rate constants were used to relate the long-term stability performance of the MCO coating under accelerated electrical testing at 900 °C to effective lifetimes at lower operating temperatures. At 750 °C an effective lifetime for the MCO coating on AL 441-HP exceeding 40,000 hours was predicted.

SOFC cells and stacks for complex fuels

Reformed hydrocarbon and coal (syngas) fuels present an opportunity to integrate solid oxide fuel cells into the existing fuel infrastructure. However, these fuels often contain impurities or additives that may lead to cell degradation through sulfur poisoning or coking. Achieving high performance and sulfur tolerance in SOFCs operating on these fuels would simplify system balance of plant and sequestration of anode tail gas. NexTech Materials, Ltd., has developed a suite of materials and components (cells, seals, interconnects) designed for operation in sulfur-containing syngas fuels. These materials and component technologies have been integrated into an SOFC stack for testing on simulated propane, logistic fuel reformates and coal syngas. Details of the technical approach, cell and stack performance is reported.