Scott L. Swartz

Sol-gel processing of composite PbTiO3/PLZT thin films

Abstract A novel sol-gel fabrication approach was developed for the fabrication of composite PbTiO3/PLZT thin films. The approach involves the deposition of a perovskite (PbTiO3) interlayer prior to deposition of the PLZT film. Composite PbTiO3/PLZT sol-gel thin films were prepared on (110) sapphire, platinum-coated sapphire, and platinum-coated silicon substrates. These films were highly crystalline and exhibited preferred crystallographic orientation. This perovskite interlayer approach is applicable to a wide variety ferroelectric thin film and substrate materials.

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.

Carbon monoxide sensor for PEM fuel cell systems

Power generation systems based on Proton-exchange membrane (PEM) fuel cells require sensors to detect carbon monoxide to extremely low levels (� 1 ppm) in the presence of hydrogen and other gaseous components (nitrogen, carbon dioxide, methane and steam). The CO sensors capable of working in reducing environments are almost non-existent. Development of a new CO sensor stable in H2-rich environment is described. The novel sensing approach is based on the adsorption of CO onto a film of an inorganic material that allows CO detection by monitoring resistance changes of the film in a simulated reformed gas, rich in H2. When suitable materials were used for the thick film approach, the resistance of the device exhibited a rapid and reversible sensitivity to carbon monoxide in the range 0‐5000 ppm over a period of several days, in the presence of hydrogen and nitrogen. # 2002 Elsevier Science B.V. All rights reserved.

SrTiO3 glass ceramics

This is the first in a series of two papers describing the crystallization and dielectric properties of glass-ceramics derived from a particular strontium titanium aluminosilicate glass composition. This first paper concerns the development of crystalline phases and microstructure of glass-ceramics prepared under various crystallization conditions. In the following paper, the dielectric properties of these glass-ceramics are described and correlated with the characterization results.Perovskite strontium titanate (SrTiO3) was the primary crystalline phase in glass-ceramics crystallized over the temperature range of 800 to 1100° C. At crystallization temperatures below 950° C, SrTiO3 formed with a spherulitic or dendritic growth habit. X-ray diffraction suggested that the SrTiO3 crystallized in a perovskite-like “precursor” phase which transformed to perovskite SrTiO3 with further crystallization time. However, electron diffraction indicated that this “precursor” phase was cubic perovskite SrTiO3. At higher crystallization temperatures, perovskite SrTiO3 was present as individual crystallites without evidence of the spherulitic habit. The crystallization of SrTiO3 was followed by that of other phases, the hexacelsian and anorthite forms of SrAl3Si2O8, and the rutile and anatase forms of TiO2. The crystallization sequence and microstructure of the glass-ceramics were determined by the competition for strontium and titanium between the crystallizing phases, SrTiO3 and SrAl2Si2O8, and TiO2.

SrTiO3 glass ceramics - Part II Dielectric properties

The dielectric properties of the strontium titanate aluminosilicate glass-ceramics described in the previous paper have been investigated over the frequency range of 10 to 1000 kHz and temperature range of −170 to 200° C. The dielectric properties were strongly dependent on the crystallization conditions, which determined the amounts of SrTiO3 and secondary crystalline phases, and the microstructure of the glass-ceramics. Room temperature values of the dielectric constant and temperature coefficient varied from 13.5 and +125 p.p.m. ° C−1 in uncrystallized glass to 47 and −600 p.p.m. ° C−1, respectively, in glass-ceramics crystallized for 16 h at 1100° C.Relatively low dielectric losses (tanδ=0.002 at 1 MHz) were observed in uncrystallized glass, and the dielectric losses increased with both frequency and temperature. The dielectric loss at temperatures below −50° C increased upon crystallization of SrTiO3, while the dielectric loss at ambient temperatures (and above) decreased significantly with the crystallization of hexacelsian SrAl2Si2O3. The crystallization of titania in glass-ceramics with high crystallization temperatures resulted in large low frequency, high temperature losses, due to Maxwell-Wagner-Sillars effects. In most glass and glass-ceramic samples, a temperature-independent increase of dielectric loss was observed over the frequency range of 10 to 1000 kHz from −50 to 200° C; the cause of these increased losses was not determined.Maxima in both the dielectric constant and loss appeared at low temperatures (below −100° C), and their magnitudes increased, as the crystallization temperature or time was increased. In the early stages of crystallization, the dielectric constant maxima could be explained on the basis of dielectric mixing between perovskite SrTiO3 and the glassy matrix. However, with higher crystallization temperatures, peaks in the dielectric constant and loss were the result of ferroic effects within the SrTiO3.

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.

Novel methods of powder preparation and ceramic forming for improving reliability of multilayer ceramic actuators

Critical components of many smart systems employ multilayer piezoelectric actuators based on lead zirconate titanate (PZT) ceramics. Applications include active vibration systems, noise suppression, acoustic camouflage, actuated structures, reconfigurable surfaces, and structural health monitoring. Two strategies involving novel materials processing techniques are discussed for improving the performance and reliability of PZT ceramic components. The first is the use of an advanced powder synthesis, which was recently developed for a range of DoD specification materials. The second strategy involves two improved ceramic manufacturing routes designed to replace the current tape casting and co-firing method. One is the use of roll- compaction for tape forming. The other is the application of the infiltrated electrode approach. Both of these methods provide improved electrical and mechanical performances and superior reliability.

Dielectric properties of Lanxide™ Al2O3/Al composites

The dielectric properties of unreinforced Lanxide™ Al2O3/Al composites have been investigated over a wide range of temperatures and frequencies. These composites were formed by the directed oxidation of suitably doped aluminium-based alloy melts, with no filler or reinforcing material in the reaction path. As-grown composite materials were good electrical conductors in all directions owing to the presence of an interconnected metallic constituent. As the metallic phases were partially removed (in favour of porosity) by continuing the oxidation reaction to completion, the composites remained electrically conducting parallel to, and became insulating transverse to, the original growth direction of the composite. This anisotropy apparently was caused by different connectivity of the metal phase between the two directions. Thermal treatments at 1600°C in argon resulted in volatilization of the residual metal in the composite, thus further increasing the porosity. As the metal content was decreased, the composites changed from conducting to insulating along the growth direction. When the metallic phase was removed completely, the porous alumina ceramic maintained anisotropic dielectric properties, due to c-axis alignment of the alumina (corundum) phase along the growth direction. The dielectric constants were 8.0 and 6.4, respectively, parallel and perpendicular to the c-axis aligned directions of the porous alumina ceramic. A dielectric relaxation phenomenon was observed in some samples of both as-grown and thermally treated material, and was attributed to an unidentified impurity effect.

Amperometric NO x Sensor Based on Oxygen Reduction

A novel ceria-based amperometric NO_x and NH₃ sensor was investigated. The sensor consisted of gadolinium-doped ceria electrolyte membrane with (La_0.60Sr_0.40) (Co_0.20Fe_0.80)O_3-δ (LSCF) electrodes applied to opposite sides. The assembly operated in combustion exhaust streams with higher sensitivity to both NO_x and NH₃, less dependence on oxygen partial pressure, and faster response than previously reported. The sensor had an operational temperature range of 200 °C-550 °C and was resistant to common exhaust gas contaminants, such as steam, CO₂, and sulfur oxides. Electrochemical testing and in-situ DRIFTS studies showed NOx adsorption on the sensor causing accelerated kinetics for oxygen reduction reaction (ORR) whereby adsorbed NOx species acted as a catalyst for an alternative ORR pathway, thus enabling an amperometric sensing mechanism.

Final Report, Validation of Novel Planar Cell Design for MW-Scale SOFC Power Systems

This report describes the work completed by NexTech Materials, Ltd. during a three-year project to validate an electrolyte-supported planar solid oxide fuel cell design, termed the FlexCell, for coal-based, megawatt-scale power generation systems. This project was focused on the fabrication and testing of electrolyte-supported FlexCells with yttria-stabilized zirconia (YSZ) as the electrolyte material. YSZ based FlexCells were made with sizes ranging from 100 to 500 cm2. Single-cell testing was performed to confirm high electrochemical performance, both with diluted hydrogen and simulated coal gas as fuels. Finite element analysis modeling was performed at The Ohio State University was performed to establish FlexCell architectures with optimum mechanical robustness. A manufacturing cost analysis was completed, which confirmed that manufacturing costs of less than