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, M
nationality International
journal CHEMISTRY OF MATERIALS
keywords TEMPERATURE PROTON CONDUCTIVITY; BARIUM NIOBATE; CERAMICS; PEROVSKITES; ELECTROLYTE; CONDUCTORS; TRANSPORT; NUMBERS; OXIDES; CELLS
abstract Ba4Nb2O9 is shown to have two basic polymorphs: a high-temperature gamma 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 gamma phase can easily be quenched to room temperature. Below similar to 950 K, both (alpha and gamma phases absorb significant amounts of water. In the case of the gamma phase, protons from absorbed water occupy ordered positions in the Structure, giving rise to a stoichiometric phase gamma-III-Ba4Nb2O9.1/3H(2)O at room temperature. gamma-III-Ba4Nb2O9-1/3H(2)O partially dehydrates, at similar to 760 K to give another stoichiometric phase gamma-II-Ba4Nb2O9.1/3H(2)O, which completely dehydrates at similar to 950 K to gamma-I- Ba4Nb2O9. The hydrated gamma phases exhibit faster protonic and oxide ionic transport than the hydrated (x phases because of the presence in the gamma 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 gamma phases at low temperatures, with the gamma -> alpha transition oil reheating a quenched sample occurring at higher temperatures in humid atmospheres.
publisher AMER CHEMICAL SOC
issn 0897-4756
year published 2009
volume 21
issue 16
beginning page 3853
ending page 3864
digital object identifier (doi) 10.1021/cm901644e
web of science category Chemistry, Physical; Materials Science, Multidisciplinary
subject category Chemistry; Materials Science
unique article identifier WOS:000269043900016
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journal analysis (jcr 2017):
journal impact factor 9.890
5 year journal impact factor 9.842
category normalized journal impact factor percentile 91.472
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