Pyrochlore and Perovskite Potassium Tantalate: Enthalpies of Formation and Phase Transformation
authors Zlotnik, S; Sahu, SK; Navrotsky, A; Vilarinho, PM
nationality International
journal CHEMISTRY-A EUROPEAN JOURNAL
author keywords calorimetry; perovskite phases; potassium; tantalum; thermochemistry
keywords MICROWAVE DIELECTRIC-PROPERTIES; THIN-FILMS; HYDROTHERMAL SYNTHESIS; KTAO3; OXIDES; DEPOSITION; POWDERS; SYSTEM; SRTIO3
abstract 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.
publisher WILEY-V C H VERLAG GMBH
issn 0947-6539
year published 2015
volume 21
issue 13
beginning page 5231
ending page 5237
digital object identifier (doi) 10.1002/chem.201405666
web of science category Chemistry, Multidisciplinary
subject category Chemistry
unique article identifier WOS:000352140000041
  ciceco authors
  impact metrics
times cited (wos core): 8
journal impact factor (jcr 2016): 5.317
5 year journal impact factor (jcr 2016): 5.184
category normalized journal impact factor percentile (jcr 2016): 82.831
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