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Title: | Pyrochlore and Perovskite Potassium Tantalate: Enthalpies of Formation and Phase Transformation |
Author: | Zlotnik, Sebastian Sahu, Sulata K. Navrotsky, Alexandra Vilarinho, Paula M. |
Keywords: | MICROWAVE DIELECTRIC-PROPERTIES THIN-FILMS HYDROTHERMAL SYNTHESIS KTAO3 OXIDES DEPOSITION POWDERS SYSTEM SRTIO3 |
Issue Date: | 2015 |
Publisher: | WILEY-V C H VERLAG GMBH |
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. |
Peer review: | yes |
URI: | http://hdl.handle.net/10773/19990 |
DOI: | 10.1002/chem.201405666 |
ISSN: | 0947-6539 |
Publisher Version: | 10.1002/chem.201405666 |
Appears in Collections: | CICECO - Artigos |
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Pyrochlore and Perovskite Potassium Tantalate Enthalpies of Formation and Phase Transformation_10.1002chem.201405666.pdf | 849.64 kB | Adobe PDF |
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