The energetics of lanthanum tantalate materials

Tori Z. Forbes, May Nyman, Mark A. Rodriguez, Alexandra Navrotsky

Research output: Contribution to journalArticlepeer-review

24 Scopus citations

Abstract

Lanthanum tantalates are important refractory materials with application in photocatalysis, solid oxide fuel cells, and phosphors. Soft-chemical synthesis utilizing the Lindqvist ion, [Ta6O19]8-, has yielded a new phase, La2Ta2O7(OH)2. Using the hydrated phase as a starting material, a new lanthanum orthotantalate polymorph was formed by heating to 850 °C, which converts to a previously reported LaTaO4 polymorph at 1200 °C. The stabilities of La 2Ta2O7(OH)2 (LaTa-OH), the intermediate LaTaO4 polymorph (LaTa-850), and the high temperature phase (LaTa-1200) were investigated using high-temperature oxide melt solution calorimetry. The enthalpy of formation from the oxides were calculated from the enthalpies of drop solution to be -87.1±9.6, -94.9±8.8, and -93.1±8.7 kJ/mol for LaTa-OH, LaTa-850, and LaTa-1200, respectively. These results indicate that the intermediate phase, LaTa-850, is the most stable. This pattern of energetics may be related to cationcation repulsion of the tantalate cations. We also investigated possible LnTaO4 and Ln2Ta2O7(OH)2 analogues of Ln=Pr, Nd to examine the relationship between cation size and the resulting phases.

Original languageEnglish (US)
Pages (from-to)2516-2521
Number of pages6
JournalJournal of Solid State Chemistry
Volume183
Issue number11
DOIs
StatePublished - Nov 2010
Externally publishedYes

Keywords

  • Calorimetry
  • Lanthanum
  • Rare earth
  • Tantalate

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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