Pronounced impact of atmospheric conditions on Ba4Nb2O9 and Ba4Ta2O9
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Date
2012-10-04
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Elsvier Science BV
Abstract
Ba(4)Nb(2)O(9) and Ba(4)Ta(2)O(9) decompose upon heating in a CO(2)-rich atmosphere. Here, we report further in situ synchrotron X-ray diffraction studies under CO(2)-free atmospheres of variable humidity and under vacuum and show that this strongly influences the reconstructive phase transitions normally seen. Under normal atmospheric conditions, alpha-Ba(4)Nb(2)O(9) transforms to gamma-Ba(4)Nb(2)O(9) at 1493 K and alpha-Ba(4)Ta(2)O(9) transforms to 6H-Ba(4)Ta(2)O(9) at 1513 K. Under wet argon, these transitions shift to lower temperatures of 1453 K and 1443 K for Ba(4)Nb(2)O(9) and Ba(4)Ta(2)O(9) respectively. Upon heating both the alpha samples under vacuum, no phase transition is observed at all up to 1723 K. Heating 6H-Ba(4)Ta(2)O(9) under vacuum saw the monoclinic -> hexagonal symmetry-transition temperature increase from 1050 K under air to 1700K. The significance of these observations in terms of possible practical applications of their mixed oxide ionic, protonic and electronic conduction properties are discussed. © 2012, Elsevier Ltd.
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Keywords
Perovskite, Barium oxides, Atmospherics, Diffraction, Niobium, Oxides
Citation
Dunstan, M. T., Kimpton, J. A., Kharton, V. V., & Ling, C. D. (2013). Pronounced impact of atmospheric conditions on Ba4Nb2O9 and Ba4Ta2O9. Solid State Ionics, 225, 172-175. doi:10.1016/j.ssi.2012.03.021