Pyrochlore and Perovskite Potassium Tantalate: Enthalpies of Formation and Phase Transformation

Sebastian Zlotnik, Sulata K. Sahu, Alexandra Navrotsky, Paula M. Vilarinho

Research output: Contribution to journalArticlepeer-review

17 Scopus citations


Alkali niobates and tantalates are currently important lead-free functional oxides. The formation and decomposition energetics of potassium tantalum oxide compounds (K2O-Ta2O5) were measured by high-temperature oxide melt solution calorimetry. The enthalpies of formation from oxides of KTaO3 perovskite and defect pyrochlores with K/Ta ratio of less than 1 stoichiometry - K0.873Ta2.226O6, K1.128Ta2.175O6, and K1.291Ta2.142O6 - were experimentally determined, and the values are (-203.63±2.92) kJmol-1 for KTaO3 perovskite, and (-339.54±5.03) kJmol-1, (-369.71±4.84) kJmol-1, and (-364.78±4.24) kJmol-1, respectively, for non-stoichiometric pyrochlores. That of stoichiometric defect K2Ta2O6 pyrochlore, by extrapolation, is (-409.87±6.89) kJmol-1. Thus, the enthalpy of the stoichiometric pyrochlore and perovskite at K/Ta=1 stoichiometry are equal in energy within experimental error. By providing data on the thermodynamic stability of each phase, this work supplies knowledge on the phase-formation process and phase stability within the K2O-Ta2O5 system, thus assisting in the synthesis of materials with reproducible properties based on controlled processing. Additionally, the relation of stoichiometric and non-stoichiometric pyrochlore with perovskite structure in potassium tantalum oxide system is discussed.

Original languageEnglish (US)
Pages (from-to)5231-5237
Number of pages7
JournalChemistry - A European Journal
Issue number13
StatePublished - Mar 23 2015
Externally publishedYes


  • calorimetry
  • perovskite phases
  • potassium
  • tantalum
  • thermochemistry

ASJC Scopus subject areas

  • Catalysis
  • Organic Chemistry


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