Single-crystal and Nano-columnar Growth of Gadolinium-doped Ceria Thin Films on Oxide Substrates Studied Using Electron
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Single-crystal and Nano-columnar Growth of Gadolinium-doped Ceria Thin Films on Oxide Substrates Studied Using Electron Microscopy D. X. Huang, C. L. Chen and A. J. Jacobson Center of Materials Chemistry, University of Houston Houston, TX 77204-5003, USA. ABSTRACT Gadolinium-doped ceria (GDC) thin films were grown by pulsed laser ablation on various oxide single crystal substrates including MgO, YSZ, LAO, NGO, and STO with different film-substrate lattice mismatch ratios. The film microstructures were characterized mainly by using electron microscopy. A clear influence of the filmsubstrate lattice mismatch on the film crystallinity has been observed. The GDC films usually exhibit columnar grain growth for a large range of film-substrate lattice mismatch ratios. A cube-on-cube growth of GDC film on MgO has been observed with a surprisingly high lattice mismatch ratio of 28%. The highest film crystallinity is obtained on the LAO substrates under a small compressive strain. This single-crystalline GDC film shows no columnar grain growth but presents a novel directionally-aligned precipitated Gd-rich nanoparticle system, which plays a specific role in relaxing various kinds of strain fields induced during the thin film growth to ensure the film crystallinity.
INTRODUCTION Gadolinium-doped Ceria (GDC) is one of the most promising electrolyte materials for replacing the commonly used Yttrium Stabilized Zirconia (YSZ) in solid oxide fuel cell (SOFC) applications [1]. GDC has higher ionic conductivity than YSZ and can therefore be used to produce SOFC devices with high electric power. SOFCs with GDC electrolytes can be operated at lower temperature (900 K) compared with YSZ (1273 K), which greatly reduces the reactions among the electrode, electrolyte and interconnect, providing the SOFC devices with high efficiency and high stability. Using conventional ceramic synthesis and thin film deposition methods, various microcrystalline and nanocrystalline bulk and thin film GDC materials have been prepared. Recently, the ionic conductivity of GDC samples was found to increase with decreasing grain size [2]. Consequently, the synthesis of nanocrystalline GDC materials has been studied in order to determine the relationship between the nanoscale structure and the mechanism that gives rise to the enhanced conductivity. Limited information, however, is available on the preparation of single crystalline GDC that is also an important material for fundamental studies of the intrinsic transport properties of GDC. Recently, we have focused on the epitaxial growth of GDC thin films on various oxide single crystalline substrates [3, 4] including MgO, YSZ, LaAlO3 (LAO), NdGaO3 (NGO), and SrTiO3 (STO). Most of the films exhibit good epitaxial relationships with the substrates but show columnar grain growth. On LAO substrates, however, a high quality single-crystalline film was obtained [5]. In this paper, we report the microstructural characterization of these single crystalline
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and nano-scale columnar grain GDC thin films.
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