Wu, J. and Li, L. P. and Espinosa, W. T. P. and Haile, S. M. (2004) Defect chemistry and transport properties of BaxCe0.85M0.15O3-d. Journal of Materials Research, 19 (8). pp. 2366-2376. ISSN 0884-2914. http://resolver.caltech.edu/CaltechAUTHORS:WUJjmr04
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The site-incorporation mechanism of M3+ dopants into A2+B4+O3 perovskites controls the overall defect chemistry and thus their transport properties. For charge-balance reasons, incorporation onto the A2+-site would require the creation of negatively charged point defects (such as cation vacancies), whereas incorporation onto the B4+-site is accompanied by the generation of positively charged defects, typically oxygen vacancies. Oxygen-vacancy content, in turn, is relevant to proton-conducting oxides in which protons are introduced via the dissolution of hydroxyl ions at vacant oxygen sites. We propose here, on the basis of x-ray powder diffraction studies, electron microscopy, chemical analysis, thermal gravimetric analysis, and alternating current impedance spectroscopy, that nominally B-site doped barium cerate can exhibit dopant partitioning as a consequence of barium evaporation at elevated temperatures. Such partitioning and the presence of significant dopant concentrations on the A-site negatively impact proton conductivity. Specific materials examined are BaxCe0.85M0.15O3-d (x = 0.85 - 1.20; M = Nd, Gd, Yb). The compositional limits for the maximum A-site incorporation are experimentally determined to be: (Ba0.919Nd0.081)(Ce0.919Nd0.081)O3, (Ba0.974Gd0.026)(Ce0.872Gd0.128)O2.875, and Ba(Ce0.85Yb0.15)O2.925. As a consequence of the greater ability of larger cations to exist on the Ba site, the H2O adsorption and proton conductivities of large-cation doped barium cerates are lower than those of small-cation doped analogs.
|Additional Information:||© 2004 Materials Research Society (Received 17 November 2003; accepted 30 April 2004) The authors thank Dr. Chi Ma (California Institute of Technology) for assistance with the scanning electron microscopy and microprobe analysis. Caltech analytical facilities are partially supported by the National Science Foundation through the Caltech Center for the Science and Engineering of Materials. Funding of this work has been provided by the U.S. Department of Energy through the Office for Energy Efficiency and Renewable Energy.|
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|Deposited On:||28 Jul 2006|
|Last Modified:||26 Dec 2012 08:57|
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