Metal-organic deposition of thin-film yttria-stabilized zirconia-titania
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Metal-organic deposition of thin-film yttria-stabilized zirconia-titania Karen E. Swider a) and Wayne L. Worrell Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104 (Received 26 June 1995; accepted 14 September 1995)
Mixed-conducting yttria-stabilized zirconia-titania (YZTi) has attractive applications in solid oxide fuel cells (SOFC’s) and electrocatalysis, particularly when used as a thin film to reduce its electrical resistance. Thin films of yttria (12 mol %) stabilized zirconia-titania (8 mol %) have been prepared using metal-organic deposition (MOD) whereby metal-organic solutions of Zr-, Y-, and Ti-2-ethylhexanoates are spun onto suitable substrates. Variables affecting the film surface-morphology, chemistry, and crystal structure are examined using scanning electron microscopy (SEM), auger electron spectroscopy (AES), and x-ray diffraction (XRD), respectively. Uniform, pore-free films having a low carbon content (,1 at. %) are made by sintering on a hot plate at 530 ±C. The effect of thermal cycling on the chemical compatibility and adherence is examined for YZTi films on yttria-stabilized zirconia substrates.
I. INTRODUCTION
Yttria-stabilized zirconia-titania (YZTi) exhibits oxygen-ion and n-type conductivity at low oxygen pressures and elevated temperatures (e.g., PO2 , 10215 atm at T 800 ±C).1–4 Oxygen-ion conduction in YZTi results from the high concentration of oxygenvacancies in the lattice which have significant mobilities at temperatures greater than ,600 ±C. This oxygen-ion conduction has been studied in detail in yttria-stabilized zirconia (YSZ), which is commonly used as an oxygen electrolyte.5 N-type conduction occurs in YZTi via electron hopping between the 31 and 41 oxidation states of the titanium cations.3,4 In the oxygen pressure and temperature environments in which it exhibits mixedconduction, YZTi may have attractive electrode and catalytic applications.6 A limitation of YSZ-based materials in electrochemical applications is their low conductivity (0.025 ohm21 cm21 ) at temperatures below 800 ±C.1,5 This problem is overcome when YSZ is used as the electrolyte in solid oxide fuel cells (SOFC’s) by employing thin films.7 Similarly, thin films of YZTi can be used to optimize its electrical conductance. Although several physical and chemical deposition methods have been developed for the preparation of YSZ thin films,7 no method has been reported for YZTi thin films. In this paper, we report our use of the metal-organic deposition (MOD) technique to prepare thin-film YZTi.
a)
Current address: Surface Chemistry Branch, Code 6170, Naval Research Laboratory, Washington, DC 20375. J. Mater. Res., Vol. 11, No. 2, Feb 1996
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MOD is a “non-vacuum, spin-on, liquid-based, thin film method,”8 which has been used successfully to prepare thin films of ferroelectrics,9,10 semiconductors,11 and high Tc superconductors.12 The deposition process
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