Structures, Phase Transitions, Hydration, and Ionic Conductivity of Ba4Ta2O9
authors Ling, CD; Avdeev, M; Kharton, VV; Yaremchenko, AA; Macquart, RB; Hoelzel, M
nationality International
journal CHEMISTRY OF MATERIALS
keywords TEMPERATURE PROTON CONDUCTIVITY; BILBAO CRYSTALLOGRAPHIC SERVER; POWDER DIFFRACTION; BA4NB2O9; POLYMORPHISM; PEROVSKITES; TANTALATE; NIOBATE; SR; MG
abstract Low-temperature alpha-Ba4Ta2O9 is isostructured With alpha-Ba4Nb2O9 (Sr4Ru2O9 type), and it undergoes a reconstructive phase transition at approximately the same temperature (1400 K) to a gamma form that can easily be quenched to room temperature. However, the gamma forms of the two compounds are completely different. Whereas gamma-Ba4Nb2O9 represents a unique Structure type, gamma-Ba4TaO9 adopts a more conventional 6H-perovskite type. The alpha ->gamma transition is Virtually irreversible in the tantalate, unlike the niobate, which can be converted back to the a form by annealing slightly below the transition temperature. quenched gamma-Ba4Nb2O highly strained due to tile extreme size mismatch between Ba2+ (1.35 angstrom) and Ta5+, (0.64 angstrom) cations in perovskite B-sites, and undergoes a series of symmetry-lowering distortions from P6(3)/nunc -> P6(3)/m -> P2(1)/c; the second of these transitions has not previously been observed in a 6H perovskite. Below similar to 950 K. both alpha-Ba4Ta4O9 and gamma-Ba4Ta2O9 hydrate to a greater extent than the corresponding phases of Ba4Ta4O9 Both hydrated forms show significant mixed protonic and oxide ionic conductivity, and electronic conductivity upon dehydration,
publisher AMER CHEMICAL SOC
issn 0897-4756
year published 2010
volume 22
issue 2
beginning page 532
ending page 540
digital object identifier (doi) 10.1021/cm903170t
web of science category Chemistry, Physical; Materials Science, Multidisciplinary
subject category Chemistry; Materials Science
unique article identifier WOS:000273580700034
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journal impact factor 9.890
5 year journal impact factor 9.842
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