Enthalpies of formation of Gd2(Ti2-xZrx)O7 pyrochlores

K. B. Helean, B. D. Begg, A. Navrotsky, B. Ebbinghaus, W. J. Weber, R. C. Ewing

Research output: Contribution to journalConference articlepeer-review

22 Scopus citations

Abstract

A calorimetric investigation of the enthalpies of formation of Gd2(Ti2-xZrx)O7, where 0≤ x ≤ 2 is underway. All samples exhibit pyrochlore (Fd3 m) peaks in their XRD patterns. However, where x=2 significant local disorder is observed in the Raman spectra. Preliminary data for the enthalpies of formation from the oxides in kJ/mol are: x=0, ΔHf = -113.4±2.7; x=0.5, ΔHf = -94.0±3.0; x=1.0, ΔHf = -74.2±4.9; x=1.5, ΔHf = -64.5±2.0; x=2, ΔHf = -52.2±4.8. Two additional samples, Gd1.80Zr2.15O7.00 (pyrochlore) and Gd2.15Zr1.87O7.00 (fluorite), were also studied. Their enthalpies of formation from the oxides in kJ/mole are -50.9±3.3 and -46.4±3.4 respectively. Replacing Ti with Zr, i.e. when x=2, destabilizes the pyrochlore in enthalpy by approximately 60 kJ/mol. The ΔHmix for the Gd2(Ti2-xZrx)O7 solid-solution series is positive and can be described by a regular solution formalism with an estimated interaction parameter, Ω = +20 kJ/mol. The results of this study suggest that the pyrochlore to fluorite transition enthalpy in Gd2Zr2O7 is small, of the order of the configurational entropy contribution due to cation disorder at the transition temperature, TΔSconf. ≈ 10 kJ/mol.

Original languageEnglish (US)
Pages (from-to)691-697
Number of pages7
JournalMaterials Research Society Symposium - Proceedings
Volume663
StatePublished - 2001
Externally publishedYes
EventScientific Basis for Nuclear Waste Management XXIV - Sydney, Australia
Duration: Aug 27 2000Aug 31 2000

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

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