(La0.8Sr0.2)(0.95)MnO3-delta (LSM) and (Er0.2Bi0.8)(2)O-3 (ESB) composite has shown promise as a potential candidate for low temperature solid oxide fuel cell (LT-SOFC) cathodes. Here the stability of LSM-ESB composite cathode was tested under a range of temperature between 500 degrees C and 650 degrees C in symmetrical cell configuration, and the changes in cathode area specific resistance (ASR) was monitored in situ using electrochemical impedance spectroscopy (EIS). Two different mechanisms govern the LSM-ESB performance degradation in different temperature regions. At 600 degrees C and below the decrease in ESB conductivity due to the order-disorder transition of ESB significantly impacts the ohmic resistance of the cells. Moreover, the surface catalytic activity of LSM-ESB is directly affected by the order-disorder transition, possibly due to changes in the oxygen incorporation rate of ESB. At 650 degrees C, above the order-disorder transition, LSM and ESB react to form tertiary phases in as little as 180 h. Our results suggest that bismuth transports through vapor phase and deposits across the porous electrode surface. These results reveal the possible degradation mechanisms for bismuth-oxide based composite cathodes. These findings are important for the future development of SOFCs and the selection of potential cathode candidates that incorporate bismuth oxide. (C) 2017 Elsevier B.V. All rights reserved.