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Thermochemistry of lanthanum zirconate pyrochlore

Published online by Cambridge University Press:  31 January 2011

A.V. Radha ,
Sergey V. Ushakov  and
Alexandra Navrotsky
A.V. Radha
Affiliation:
Peter A. Rock Thermochemistry Laboratory and NEAT ORU, University of California at Davis, Davis, California 95616
Sergey V. Ushakov
Affiliation:
Peter A. Rock Thermochemistry Laboratory and NEAT ORU, University of California at Davis, Davis, California 95616
Alexandra Navrotsky*
Affiliation:
Peter A. Rock Thermochemistry Laboratory and NEAT ORU, University of California at Davis, Davis, California 95616
*
a) Address all correspondence to this author. e-mail: anavrotsky@ucdavis.edu
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Abstract

A thermodynamic study was carried out to resolve discrepancies in the enthalpy of formation and related parameters for lanthanum zirconate pyrochlore. The homogeneity field for single phase pyrochlore formation was determined to be ∼33–35 mol% La2O3 at 1500 °C. High-temperature oxide melt drop solution calorimetry was performed in sodium molybdate and lead borate solvents on three compositions ranging from La1.98Zr2.01O7 to La2.07Zr1.95O7. The enthalpy of formation from oxides at 25 °C, ΔH0f,ox, for stoichiometric lanthanum zirconate pyrochlore is −107.3 ± 5.1 kJ/mol, and the standard enthalpy of formation from elements, ΔH0f,el, is −4102.2 ± 6.0 kJ/mol. La2Zr2O7 pyrochlore was found by differential thermal analysis to be stable up to its melting point. The melting point and the fusion enthalpy of La2Zr2O7 pyrochlore were measured as 2295 ± 10 °C and ∼350 kJ/mol, respectively.

Keywords

CalorimetryDifferential thermal analysis (DTA)

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Articles
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Journal of Materials Research , Volume 24 , Issue 11 , November 2009 , pp. 3350 - 3357
Copyright
Copyright © Materials Research Society 2009

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