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Title: Structures, phase transitions, hydration, and ionic conductivity of Ba4Nb2O9
Authors: Ling, CD
Avdeev, M
Kutteh, R
Kharton, VV
Yaremchenko, AA
Fialkova, S
Sharma, N
Macquart, RB
Hoelzel, M
Gutmann, MJ
Keywords: Hydration
Ionic conductivity
Phase transformations
Molecular structure
Issue Date: 25-Aug-2009
Publisher: American Chemical Society
Citation: Ling, C. D., Avdeev, M., Kutteh, R., Kharton, V. V., Yaremchenko, A. A., Fialkova, S., Sharma, N., Macquart, R. B., Hoelzel, M., & Gutmann, M. J.(2009). Structures, phase transitions, hydration, and ionic conductivity of Ba4Nb2O9. Chemistry of Materials, 21(16), 3853-3864. doi:10.1021/cm901644e
Abstract: Ba4Nb2O9 is shown to have two basic polymorphs: a high-temperature γ phase, which represents an entirely new structure typed and a low-temperature (x phase, which has the rare Sr4Ru2O9 structure type. The phases are separated by a reconstructive phase transition at similar to 1370 K, the kinetics of which are sufficiently slow that the γ phase can easily be quenched to room temperature. Below similar to 950 K, both (α and γ phases absorb significant amounts of water. In the case of the γ phase, protons from absorbed water occupy ordered positions in the structure, giving rise to a stoichiometric phase γ-III-Ba4Nb2O9.1/3H(2)O at room temperature. γ-III-Ba4Nb2O9-1/3H(2)O partially dehydrates, at similar to 760 K to give another stoichiometric phase γ-II-Ba4Nb2O9.1/3H(2)O, which completely dehydrates at similar to 950 K to γ-I- Ba4Nb2O9. The hydrated γ phases exhibit faster protonic and oxide ionic transport than the hydrated (x phases because of the presence in the γ phases of 2D layers containing Nb5+ cations with unusually low oxygen coordination numbers (4 or 5) separated by discrete OH groups. Hydration appears to play an important role in stabilizing the γ phases at low temperatures, with the γ -> α transition oil reheating a quenched sample occurring at higher temperatures in humid atmospheres. © 2009, American Chemical Society
Gov't Doc #: 1316
ISSN: 0897-4756
Appears in Collections:Journal Articles

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