Anomalies in the thermomechanical behavior of Ba0.5Sr0.5Co0.8Fe0.2O3-δ ceramic oxygen conductive membranes at intermediate temperatures

The thermomechanical properties of Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCF) were measured using ring-on-ring tests and depth-sensitive microindentation. The cubic BSCF material exhibits an anomaly in mechanical properties between 200 and 400 degrees C. The observed anomaly is attributed to the transition of Co3+ spin states which is experimentally confirmed by susceptibility measurements. Furthermore, slip lines were observed around the impression when indentation tests were carried out above 260 degrees C.