AVS 51st International Symposium
    Applied Surface Science Thursday Sessions
       Session AS-ThA

Paper AS-ThA2
Nanoscale Effects on Ion Conductance of Layer by Layer Structures of Gadolinia-doped Ceria and Zirconia

Thursday, November 18, 2004, 2:20 pm, Room 210A

Session: Fuel Cell, Catalytic, and Nanomaterials Characterization
Presenter: S.A. Azad, Pacific Northwest National Laboratory
Authors: S.A. Azad, Pacific Northwest National Laboratory
A.A. El-Azab, Pacific Northwest National Laboratory
L.S. Saraf, Pacific Northwest National Laboratory
O.M. Marina, Pacific Northwest National Laboratory
C.W. Wang, Pacific Northwest National Laboratory
D.E. McCready, Pacific Northwest National Laboratory
S.V. Shutthanandan, Pacific Northwest National Laboratory
S.T. Thevuthasan, Pacific Northwest National Laboratory
Correspondent: Click to Email
Development of electrolyte materials that possess high oxygen ion conductance at relatively low temperatures is essential to improve the performance of electrochemical devices. Ceria, doped with a divalent or trivalent cation, exhibits higher ion conductance compared with yittria-stabilized zirconia, the major component currently used in solid oxide fuel cells (SOFC). In this research, we have synthesized layer by layer structures of gadolinia doped ceria and zirconia in order to determine the nanoscale effects on the ion conductance of these films. Highly oriented multilayered nanostructures of gadolinia-doped ceria and zirconia were grown on sapphire substrates using molecular beam epitaxy and were characterized by in situ reflection high energy electron diffraction (RHEED) and ex situ x-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and Rutherford backscattering spectrometry (RBS). The oxygen ion conductance, measured by surface impedance spectroscopy at relatively low temperatures, was found to increase with increasing number of layers in these films. Theoretical calculations were also performed to understand the effects of space charge regions induced by the thermodynamic equilibrium and impurity segregation as well as the influence of the grain microstructures on the electric transport processes in solid oxide materials. The defect electrochemistry model developed in our study allows the extrinsic element (Gd) to transfer across the interfaces and space charge regions are created as a result, counterbalancing the purely blocking effect observed in polycrystalline structures of ceria or zirconia. The elastic interactions in ceria and zirconia lattice as well as the individual layer thickness largely influence the transfer of Gd across the interfaces.