AVS 59th Annual International Symposium and Exhibition
    Energy Frontiers Focus Topic Wednesday Sessions
       Session EN+TF-WeA

Paper EN+TF-WeA9
Synthesis of a Thin-Film Yttria-Stabilized-Zirconia (Y2O3-ZrO2) Thin Films by Radical Enhanced Atomic Layer Deposition for μ-Solid Oxide Fuel Cell Applications

Wednesday, October 31, 2012, 4:40 pm, Room 15

Session: Thin Films for Energy Applications
Presenter: J. Cho, University of California, Los Angeles
Authors: J. Cho, University of California, Los Angeles
D. Membreno, University of California, Los Angeles
B. Dunn, University of California, Los Angeles
J.P. Chang, University of California, Los Angeles
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Solid Oxide Fuel Cells (SOFCs) is one outstanding alternative energy devices, owing to its significantly higher fuel conversion efficiency than that of fossil fuel based ones while being more environmentally benign. Despite its tremendous advantages and potentials, however, the commercial applications of this technology have been restrained due to its intrinsic problems such as the use of expensive interconnectors and long start-up time, which are inevitably tied to its high operation temperatures (650-1000°C) to maintain high ionic conductivity of electrolytes. To fully utilize the revolutionary potentials of SOFCs in commercial applications, it is imperative to lower its operation temperatures to intermediate temperatures, below 700°C without sacrificing the efficiency of the cell.

Yttria-Stabilized-Zirconia (YSZ, (Y2O3)x-(ZrO2)(1-x)) has been implemented as the electrolyte material of choice in SOFCs because of their high structural, chemical stability with along with high ionic conductivity at the operation temperatures of the cell. While the temperature of the cell could not be lowered as it compromises its conductivity, recent pioneering studies of YSZ in nanoscales have reported significantly enhanced ionic conductivities which could not only lower the working temperature of the cell much below 700°C, but will also allow an expansion in their potential applications even to power portable electronics, resulting in strong scientific and technological interests in investigating the feasibility of developing YSZ in nanoscale for electrolyte applications in next-generation SOFCs, including µ-SOFCs for portable electronics. A thin-film YSZ has been synthesized by Radical Enhanced Atomic Layer Deposition (REALD), with thickness and composition controllability. The metal precursors, Tris(2,2,6,6-tetramethyl-3,5-heptanedionato)yttrium(III) [Y(tmhd)3] and Bis(cyclopentadienyl)dimethylzirconium [Cp2Zr(CH3)2] with Oxygen radicals as oxidant, were used to deposit Y2O3 and ZrO2 with the deposition rates of 0.47 Å/cycle and 0.62 Å/cycle, respectively at ~250°C. The composition of each metal cations in YSZ thin films synthesized as a solid solution of Y2O3-ZrO2 was found to correlate closely to the number of ALD cycles of each constituent oxide. The crystalline structures as well as the local environment of the deposited YSZ thin films were studied by X-ray diffraction (XRD) and Extended X-ray absorption fine structure (EXAFS). The conductivities of REALD YSZ films were found to be both a function of the thickness of YSZ film and the yttrium content in the film. The presence of conductivity enhancement effect on YSZ-SrTiO3 nanoparticles are investigated as well.