Growth of Ceria-Zirconia Electrolyte Nanostructures with High Interface Density by Using Sol-gel/GLAD Combination
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K8.3.1
Growth of Ceria-Zirconia Electrolyte Nanostructures with High Interface Density by Using Sol-gel/GLAD Combination
Laxmikant Saraf, D. W. Matson, J. S. Young, C. M. Wang, and S. Thevuthasan Pacific Northwest National Laboratory, Richland WA 99352.
ABSTRACT We report a process for the successful incorporation of ceria in to yttria-stabilized zirconia (YSZ) columnar nanostructures grown by glancing angle deposition (GLAD) technique, resulting in high interface density columnar nanostructures. The incorporation of ceria into YSZ columns is confirmed by scanning electron microscopy (SEM) in a cross sectional geometry with in-situ analysis of elemental x-ray mapping technique and energy dispersive x-ray analysis (EDX). Controlled engineering of such nanostructures is potentially important in the future development of high efficiency solid oxide fuel cell electrolytes. The challenges and advantages of this process are discussed.
INTRODUCTION Fundamental understanding of oxygen transport behavior in solid oxide fuel cells (SOFCs) [1,2] has become increasingly important as the development of this efficient alternative energy technology progresses. Recent materials processing developments [3] have made it possible to investigate oxygen transport behavior in SOFCs in greater details. Glancing angle deposition (GLAD) [4,5] is one of those recently developed techniques that allows creation of oxide/ metallic films having high surface area vertical interfaces with respect to the substrate. The GLAD deposition process relies on a very low angle of adatom incidence, producing self shadowing and the production of open porous structures. Columnar structures can be produced by rotating the substrate during GLAD depositions. Such GLAD-deposited columnar features having a high degree of vertical porosity provide an ideal matrix for impregnation by a second oxide electrolyte, creating high density vertical oxide/oxide interfaces. The well established solgel method [6-8] provides an ideal and simple mechanism for incorporating a high purity second oxide into a GLAD structure. In this work, we use a combination of GLAD and sol-gel methods to grow high density vertical interface sandwich structures of YSZ and ceria. The choice of YSZ and ceria comes from the fact that they are known [1,2] to be excellent candidates for electrolyte materials in SOFCs due to their stabilities over a wide temperature range, similar (fluorite) structures, and their known ion conducting properties. Doped-ceria is especially suitable for high oxygen ion conduction at intermediate temperatures [9] (700-1000 K), a property needed to bring down the use cost associated with SOFCs. In this work, we use crosssectional SEM, elemental x-ray mapping with EDX to study the incorporation of ceria into a porous GLAD-deposited YSZ film. The top ceria layer is then chemically etched in such a way that columnar YSZ-ceria structure is exposed to the surface, allowing characterization of the composite structure.
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EXPERIMENTAL Growth of porous YSZ films was carr
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