abstract
Cubic perovskite-type Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCF) is one of the mixed ionic-electronic conductors with the highest oxygen permeability known to date. It serves as a parent material for the development of functional derivatives for electrochemical applications including oxygen separation membranes, solid electrolyte cell electrodes and electrocatalysts for the oxygen evolution reaction. The present study is focused on the determination of the precise stability boundaries of cubic perovskite BSCF employing a coulometric titration technique in combination with thermogravimetric analysis, X-ray and neutron diffraction, and molecular dynamics simulations. Both the low-p(O-2) and high-p(O-2) stability boundaries at 700-950 degrees C were found to correspond to a fixed value of oxygen content in the perovskite lattice of 3 - delta = similar to 2.13 and similar to 2.515, respectively. The stability limits in this temperature range are expressed by the following equations: high-p(O-2) boundary: log p(O-2) (atm) (+/- 0.1) = -10 150/T (K) + 8.055; low-p(O-2) boundary: log p(O-2) (atm) (+/- 0.03) = -20 750/T (K) + 4.681. The p(O-2)-T phase diagram of the BSCF system under oxidizing conditions is addressed in a wider temperature range and is shown to include a region of precipitation of a "low-temperature'' phase occurring at 400-500 degrees C. The fraction of the low-temperature precipitate, which co-exists with the cubic perovskite phase and is stable up to 790-820 degrees C, increases upon increasing p(O-2) in the range 0.21-1.0 atm.
keywords
OXIDE FUEL-CELLS; SECONDARY PHASE-FORMATION; OXYGEN PERMEATION; INTERMEDIATE TEMPERATURES; BSCF PEROVSKITE; DOPED BA0.5SR0.5CO0.8FE0.2O3-DELTA; ELECTRICAL-PROPERTIES; NEUTRON-DIFFRACTION; CHEMICAL-STABILITY; GRAIN-SIZE
subject category
Chemistry; Physics
authors
Yaremchenko, AA; Patrakeev, MV; Naumovich, EN; Khalyavin, DD
our authors
Aleksey Yaremchenko
Principal ResearcherProjects
acknowledgements
A. A. Y. would like to acknowledge the financial support from the FCT, Portugal (project IF/01072/2013/CP1162/CT0001 and project CICECO-Aveiro Institute of Materials POCI-01-0145-FEDER-007679 (FCT ref. UID/CTM/50011/2013), financed by the national funds through the FCT/MEC and when appropriate co-financed by FEDER under the PT2020 Partnership Agreement). M. V. P. is grateful for support by Russian Science Foundation (project 17-79-30071). E. N. N. would like to acknowledge financial support from NCBR, Poland (project POIR.01.02.00-00-0013/16 NewSOFC, co-funded from the European Regional Development Fund under the Operational Programme Smart Growth).