Energetics of defect fluorite and pyrochlore phases in lanthanum and gadolinium hafnates

Sergey V. Ushakov, Alexandra Navrotsky, Jean A. Tangeman, Katheryn B. Helean

Research output: Contribution to journalArticlepeer-review

48 Scopus citations


Aerodynamic levitation combined with laser heating was used to prepare melts in the HfO2-La2O3 (-Gd2O 3) systems. All melts crystallized upon quenching in oxygen. Hf 2La2O7 pyrochlore and Gd0.5Hf 0.5O1.75 fluorite phases were identified. Gd 0.5Hf0.5 O1.75 fluorite was transformed into the pyrochlore structure by annealing at 1450°C. Pyrochlore that crystallized from HfO2-La2O3 melts contained 31.6-34.2 mol% La2O3. The unit cell parameter increased linearly with La content from 10.736 to 10.789 Å. Drop solution calorimetric experiments were performed in 3Na2O · 4MoO 3 melt at 702°C. The enthalpies of formation from the oxides for pyrochlore phases are -107.0 ± 5.0 kJ/mol for Hf2La 2O7 and -48.8 ± 4.7 kJ/mol for Hf 2Gd2O7. The enthalpy of the pyrochlore-fluorite phase transition in Hf2Gd2O7 is 23.6 ± 3.1 kJ/mol.

Original languageEnglish (US)
Pages (from-to)1171-1176
Number of pages6
JournalJournal of the American Ceramic Society
Issue number4
StatePublished - Apr 2007
Externally publishedYes

ASJC Scopus subject areas

  • Ceramics and Composites
  • Materials Chemistry


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