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Defect chemistry and transport properties of BaxCe0.85M0.15O3-δ

Published online by Cambridge University Press:  03 March 2011

J. Wu ,
L.P. Li ,
W.T.P. Espinosa  and
S.M. Haile
J. Wu*
Affiliation:
Material Science, California Institute of Technology, Pasadena, California 91125
L.P. Li
Affiliation:
Material Science, California Institute of Technology, Pasadena, California 91125
W.T.P. Espinosa
Affiliation:
Material Science, California Institute of Technology, Pasadena, California 91125
S.M. Haile
Affiliation:
Material Science, California Institute of Technology, Pasadena, California 91125
*
a)Address all correspondence to this author.e-mail: jwu@caltech.edu
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Abstract

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-δ (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.

Keywords

Ionic conductorDefectsCeramic
Type
Articles
Information
Journal of Materials Research , Volume 19 , Issue 8 , August 2004 , pp. 2366 - 2376
Copyright
Copyright © Materials Research Society 2004

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