Formation enthalpies of rare earth titanate pyrochlores

K. B. Helean, S. V. Ushakov, C. E. Brown, A. Navrotsky, J. Lian, R. C. Ewing, J. M. Farmer, L. A. Boatner

Research output: Contribution to journalArticlepeer-review

125 Scopus citations

Abstract

High-temperature oxide melt solution calorimetry and Rietveld refinements of powder X-ray diffraction data were used to investigate the structure (Fd3m; Z=8) and energetics of a series of RE2Ti2O7 (RE=Sm-Lu) compounds with the pyrochlore structure as well as La 2Ti2O7 with a layered perovskite-type structure. All of the RE-titanates were found to be stable in enthalpy with respect to their oxides. In the pyrochlore series, Lu2Ti 2O7 was least stable in enthalpy (ΔHf-ox at 298K=-56.0±4.0kJ/mol); the most stable materials were Gd-, Eu-, and Sm2Ti2O7 with ΔHf-ox at 298K=-113.4±2.7, -106.1±4.2, -115.4±4.2kJ/mol, respectively. In general, as the radius ratio of the A- to B-site cations, RA/RB, decreases, the pyrochlore structure becomes less stable. The trend of ionic radius of the RE3+ cation vs. ΔHf-ox at 298K is non-linear and approximately parallels the increasing "resistance" to ion-beam-induced amorphization as RA/R B decreases.

Original languageEnglish (US)
Pages (from-to)1858-1866
Number of pages9
JournalJournal of Solid State Chemistry
Volume177
Issue number6
DOIs
StatePublished - Jun 2004
Externally publishedYes

Keywords

  • Enthalpy
  • Nuclear waste
  • Pyrochlore
  • Thermodynamics

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Ceramics and Composites
  • Condensed Matter Physics
  • Physical and Theoretical Chemistry
  • Inorganic Chemistry
  • Materials Chemistry

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