Processing of yttria stabilized zirconia thin films by liquid fuel combustion chemical vapor deposition
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Processing of yttria stabilized zirconia thin films by liquid fuel combustion chemical vapor deposition Zhigang Xu1, Q. Wei1,2, Jag Sankar1 1 NSF Center For Advanced Materials And Smart Structures, North Carolina A&T University, Greensboro, NC 27411 2 Department of Mechanical Engineering, The Johns Hopkins University, Baltimore, MD 21218 ABSTRACT Yttria fully stabilized zirconia (YSZ) thin films have been successfully synthesized with atmospheric combustion chemical vapor deposition (ACCVD) technique with liquid fuel. Key processing parameters, such as the ratio of oxygen to liquid fuel in the flame, the concentration of metal reagents in the solution, the temperature of the substrate and substrate material, have been investigated. The as-grown films are characterized with X-ray diffraction and scanning electron microscopy. Within the range of experimental parameters, the phase of the film is predominantly of cubic structure. The phase and crystallinity of the films are strongly dependent upon the experimental variables. INTRODUCTION Yttria stabilized zirconia has high oxygen-ion conductivity over a wide range of temperature and oxygen pressure. The oxygen vacancies in the material produced by doping enhance the mobility of the oxygen ions. It has been used as the electrolyte in solid oxide fuel cells (SOFCs), as well as oxygen sensors for combustion control, and so on [1]. Hightemperature SOFCs offer a clean, pollution-free technology to produce electrical power directly from chemical energies at high efficiencies. The materials concerns of the electrolyte are still an important issue in the SOFCs. From the point of view of ion conductivity, stabilized zirconia in fluorite structure is preferred to other phases. To minimize the current path and hence ohmic loss in the electrolyte, thin film of YSZ is favored. In the past years, thin film YSZ used to be processed with electrochemical vapor deposition [2-4] and low-pressure metalorganic chemical vapor deposition techniques [5-8]. In both of techniques, however, the size and shape of the parts to be fabricated are limited because they both need vacuum reactors. ACCVD has been used for deposition of thin films of oxides, such as Al2O3, SiO2, YBCO, etc [9-11]. ACCVD that works in open air has the advantage of high deposition rate and low operational cost. Moreover, it is a promising technique for conformal deposition on large and non-flat parts. In this report, parametric investigations for YSZ thin film synthesis with ACCVD technique are presented. EXPERIMENTAL DETAILS A liquid fuel ACCVD system is established for oxide film processing. The schematic illustration of the system is shown in Fig. 1. Basically this system consists of a quaternary high performance liquid chromatography (HPLC) pump, an atomizer, a pilot flame and the substrate heating/cooling support. Zirconium 2-ethylhexanoate (Zr-2EH) and Yttrium 2-ethylhexanoat (Y2EH) are chosen as reagents, which are dissolved in toluene separately. The solutions are delivered by the HPLC pump to the atomizer with a prec
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