Please use this identifier to cite or link to this item: https://apo.ansto.gov.au/dspace/handle/10238/11873
Title: The structures, phase transitions and dynamics behind mixed ionic and electronic conduction in hydrated Ba4Nb2O9
Authors: Ling, CD
Avdeev, M
Johnson, MR
Keywords: Phase transformations
Hydration
Ionic conductivity
Perovskite
Tantalates
Oxygen
Neutron diffraction
Issue Date: 3-Feb-2010
Publisher: Australian Institute of Physics
Citation: Ling, C. D., Avdeev, M., & Johnson, M. R. (2010). The structures, phase transitions and dynamics behind mixed ionic and electronic conduction in hydrated Ba4Nb2O9. Paper presented to the 34th Annual Condensed Matter and Materials Meeting 2010, Waiheke Island Resort, Waiheke, Auckland, New Zealand 2 - 5 February 2010. Retrieved from: https://physics.org.au/wp-content/uploads/cmm/2010/
Abstract: Although Ba4Nb2O9 was first synthesised in 1965, [1] its structure remained unsolved until a recent study [2] in which we showed that Ba4Nb2O9 has two basic polymorphs: a high temperature γ phase, which represents an entirely new structure type; and a low-temperature α phase, which has the rare Sr4Ru2O9 structure type. The phases are separated by a reconstructive transition at ~1370 K, the kinetics of which are sufficiently slow that the γ phase can easily be quenched to room temperature. Below ~950 K, both α and γ absorb significant amounts of water. In the γ phase, protons occupy ordered positions, giving rise to a stoichiometric phase γ -III-Ba4Nb2O9.1/3H2O at room temperature. γ-III-Ba4Nb2O9.1/3H2O partially dehydrates at ~760 K to γ-II-Ba4Nb2O9.1/6H2O, then completely dehydrates at ~950 K to γ-I-Ba4Nb2O9. The hydrated γ phases exhibit faster protonic and oxide ionic transport than the hydrated " phases, due to 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. In this paper, we will discuss the structures and mechanisms of hydration – and, therefore, of ionic conduction – in the various phases of Ba4Nb2O9 on the basis of neutron diffraction experiments and ab initio (density functional theory) dynamics simulations.
URI: https://physics.org.au/wp-content/uploads/cmm/2010/
https://apo.ansto.gov.au/dspace/handle/10238/11873
ISBN: 978-0-646-53897-6
Appears in Collections:Conference Publications

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