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Rietveld X-ray Powder Profile Analysis and Electrical Conductivity of Fastion Conducting Gd2(Til-ySny)2O7 Solid Solutions

Published online by Cambridge University Press:  15 February 2011

Kevin Eberman ,
Per Önnerud ,
Tae-Hwan Yu ,
Harry L. Tuller  and
Bernhardt J. Wuensch
Kevin Eberman
Affiliation:
Department of Materials Science and Engineering, Crystal Physics and Electroceramics Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139.
Per Önnerud
Affiliation:
Department of Materials Science and Engineering, Crystal Physics and Electroceramics Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139.
Tae-Hwan Yu
Affiliation:
Department of Materials Science and Engineering, Crystal Physics and Electroceramics Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139.
Harry L. Tuller
Affiliation:
Department of Materials Science and Engineering, Crystal Physics and Electroceramics Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139.
Bernhardt J. Wuensch
Affiliation:
Department of Materials Science and Engineering, Crystal Physics and Electroceramics Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139.
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Abstract

The A3+2B4+2O7 pyrochlores have fast-ion conduction properties that make them attractive candidates for applications in fuel cells. Rietveld powder-profile analysis of x-ray diffraction data has been used to determine structural parameters for Gd2(Ti1-ySny)2O7 solid solutions (y = 0.20, 0.40, 0.60, and 0.80) for correlation with composition-dependence of the specimens' electrical conductivity. In accord with Vegard's law, the lattice constants increase linearly with y as the larger Sn ion replaces Ti4+. The structures in the system remain remarkably ordered in view of the fact that it had been suggested that increasing the average radius of the ions that occupy the B4+ site relative to A3+ drives the system toward a disordered defect-fluorite state. A small but significant increase in mixing of the occupancy of the cation sites was found with increasing y to a maximum of [GdB] = 0.05. We could detect no significant disorder in the anion array. The activation energy and pre-exponential term for oxygen ion conduction were found to increase linearly and exponentially with y, respectively, such that at a given temperature, the ionic conductivity changes by less than an order of magnitude across the system. The behavior is in marked contrast to other systems where the substitution of a larger cation in the B site increases conductivity by up to three orders of magnitude as a consequence of substantial disorder that is introduced in both the cation and anion arrays.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 453: Symposium R – Solid State Chemistry of Inorganic Materials , 1996 , 567
Copyright
Copyright © Materials Research Society 1997

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References

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