Title
Transmission electron microscopy study of <tex>$BA_{0.5}Sr_{0.5}CO_{0.8}Fe_{0.2}O_{3-\delta}$</tex> Perovskite decomposition at intermediate temperaturesTransmission electron microscopy study of <tex>$BA_{0.5}Sr_{0.5}CO_{0.8}Fe_{0.2}O_{3-\delta}$</tex> Perovskite decomposition at intermediate temperatures
Author
Faculty/Department
Faculty of Sciences. Physics
Research group
Electron microscopy for materials research (EMAT)
Publication type
article
Publication
Washington, D.C.,
Subject
Physics
Chemistry
Source (journal)
Chemistry of materials / American Chemical Society. - Washington, D.C.
Volume/pages
22(2010):21, p. 5866-5875
ISSN
0897-4756
ISI
000283623700010
Carrier
E
Target language
English (eng)
Full text (Publishers DOI)
Affiliation
University of Antwerp
Abstract
The cubic perovskite Ba(0.5)Sr(0.5)Co(0.8)Fe(0.2)O(3-delta) (denoted BSCF) is the state-of-the-art ceramic membrane material used for oxygen separation technologies above 1150 K. BSCF is a mixed oxygen-ion and electron conductor (MIEC) and exhibits one of the highest oxygen permeabilities reported so far for dense oxides. Additionally, it has excellent phase stability above 1150 K. In the intermediate temperature range (750-1100 K), however, BSCF suffers from a slow decomposition of the cubic perovskite into variants with hexagonal stacking that are barriers to oxygen transport. To elucidate details of the decomposition process, both sintered BSCF ceramic and powder were annealed for 180-240 h in ambient air at temperatures below 1123 K and analyzed by different transmission electron microscopy techniques. Aside from hexagonal perovskite Ba(0.5)Sr(0.5)CoO(3-delta) , the formation of lamellar noncubic phases was observed in the quenched samples. The structure of the lamellae with the previously unknown composition Ba(1-x)Sr(x)Co(2-y)Fe(y)O(5-delta) was found to be related to the 15R hexagonal perovskite polytype. The valence and spin-state transition of cobalt leading to a considerable diminution of its ionic radius can be considered a reason for BSCF's inherent phase instability at intermediate temperatures.
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