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http://hdl.handle.net/10773/21985
Title: | Oxygen ionic conduction in brownmillerite CaAl0.5Fe0.5O2.5+δ |
Author: | Kharton, V.V. Marozau, I.P. Vyshatko, N.P. Shaula, A.L. Viskup, A.P. Naumovich, E.N. Marques, F.M.B. |
Keywords: | A. Oxides D. Crystal structure D. Electrical properties D. Ionic conductivity D. Thermal expansion Activation energy Crystal structure Diffusion Oxygen Stoichiometry Thermal expansion Tetrahedral layers Calcium compounds |
Issue Date: | Apr-2003 |
Publisher: | Elsevier |
Abstract: | The oxygen permeability of CaAl0.5Fe0.5O2.5+δ brownmillerite membranes at 1123-1273 K was found to be limited by the bulk ionic conduction, with an activation energy of 170 kJ/mol. The ion transference numbers in air are in the range 2 × 10-3 to 5 × 10-3. The analysis of structural parameters showed that the ionic transport in the CaAl0.5Fe0.5O2.5+δ lattice is essentially along the c axis. The largest ion-migration channels are found in the perovskite-type layers formed by iron-oxygen octahedra, though diffusion in tetrahedral layers of the brownmillerite structure is also possible. Heating up to 700-800 K in air leads to losses of hyperstoichiometric oxygen, accompanied with a drastic expansion and, probably, partial disordering of the CaAl0.5Fe0.5O2.5+δ lattice. The average thermal expansion coefficients of CaAl0.5Fe0.5O2.5+δ ceramics in air are 16.7 × 10-6 and 12.6 × 10-6 K-1 at 370-850 and 930-1300 K, respectively. |
Peer review: | yes |
URI: | http://hdl.handle.net/10773/21985 |
DOI: | 10.1016/S0025-5408(03)00069-2 |
ISSN: | 0025-5408 |
Appears in Collections: | CICECO - Artigos |
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MRB38_773.pdf | Article | 204.06 kB | Adobe PDF | View/Open |
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