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Title: Phase diagram, chemical stability and physical properties of the solid-solution Ba(4)Nb(2-x)Ta(x)O(9)
Authors: Dunstan, MT
Southon, PD
Kepert, CJ
Hester, JR
Kimpton, JA
Ling, CD
Keywords: Perovskite
Phase diagrams
Ionic conductivity
Barium oxides
Issue Date: 1-Oct-2011
Publisher: Academic Press INC Elsevier
Citation: Dunstan, M. T., Southon, P. D., Kepert, C. J., Hester, J., Kimpton, J. A., Ling, C. D. (2011). Phase diagram, chemical stability and physical properties of the solid-solution Ba(4)Nb(2-x)Ta(x)O(9). Journal of Solid State Chemistry, 184(10), 2648-2654. doi:10.1016/j.jssc.2011.07.036
Abstract: Through the construction of the Ba4Nb2−xTaxO9 phase diagram, it was discovered that the unique high-temperature γ phase is a thermodynamic intermediate between the low-temperature α phase (Sr4Ru2O9-type) and a 6H-perovskite. Refined site occupancies for the γ phase across the Ba4Nb2−xTaxO9 solid-solution indicate that Nb preferentially occupies the tetrahedral sites over the octahedral sites in the structure. When annealed in a CO2-rich atmosphere, all of the phases studied absorb large amounts of CO2 at high temperatures between ∼ 700 and 1300 K. In situ controlled-atmosphere diffraction studies show that this behaviour is linked to the formation of BaCO3 on the surface of the material, accompanied by a Ba5(Nb,Ta)4O15 impurity phase. In situ diffraction in humid atmospheres also confirms that these materials hydrate below ∼ 1273 K , and that this plays a critical role in the various reconstructive phase transitions as well as giving rise to proton conduction.(C) 2011 Elsevier Inc.
Gov't Doc #: 3806
ISSN: 0022-4596
Appears in Collections:Journal Articles

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