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Thermochemical study of trivalent-doped ceria systems: CeO2–MO1.5 (M = La, Gd, and Y)

Published online by Cambridge University Press:  03 March 2011

Weiqun Chen  and
Alexandra Navrotsky
Weiqun Chen
Affiliation:
NEAT ORU and Thermochemistry Facility, University of California at Davis, Davis, California, 95616-8779
Alexandra Navrotsky*
Affiliation:
NEAT ORU and Thermochemistry Facility, University of California at Davis, Davis, California, 95616-8779
*
a) Address all correspondence to this author. e-mail: anavrotsky@ucdavis.edu
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Abstract

The formation enthalpies from the oxide end-members (ΔHf,ox) of the CeO2–MO1.5 (M = La, Gd, and Y) systems were determined by high temperature oxide melt drop solution calorimetry. In each system, ΔHf,ox is slightly positive over the investigated composition range with a maximum at a certain doping level. Above that concentration, ΔHf,ox decreases rapidly and stays almost constant. Such behavior is strikingly different from the strongly negative ΔHf,ox of the ZrO2–YO1.5 and HfO2–YO1.5 systems. The absence of substantial energetic stabilization in the CeO2–MO1.5 systems may be attributed to the large size of Ce4+, which has no preference for 7-coordination like the smaller Zr4+ or Hf4+ ions. The primary defect associates in CeO2–MO1.5 are proposed to be neutral trimers with oxygen vacancies nearest neighbor to the dopant cations. It is also suggested that the maximum ΔHf,ox (destabilization) of CeO2–MO1.5 is determined by the local site distortion rather than the global lattice deformation. The relatively stable region after the maximum ΔHf,ox may be attributed to the somewhat stabilizing long-range defect–defect interactions, which become effective above a certain doping level.

Keywords

CalorimetryCeDefects
Type
Articles
Information
Journal of Materials Research , Volume 21 , Issue 12 , December 2006 , pp. 3242 - 3251
Copyright
Copyright © Materials Research Society 2006

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