High Temperature Mechanical Properties of La0.7Sr0.3Cr1-yCoyO3 in Reducing Environments

Abstract

La0.7Sr0.3Cr1-yCoyO3 (y=0-0.2) was synthesized so that it could be sintered at temperatures as low as 1500 degrees C, producing a highly dense system. The materials were fabricated into bars and mechanically tested using a four-point bend test, from room temperature to 1000 degrees C. High mechanical strength was obtained at 1000 degrees C; however, degradation of the mechanical properties was observed in the system at cobalt B-site dopant concentrations as low as 5 mol%, in reducing atmospheres at 1000 degrees C. La0.7Sr0.3Cr0.95Co0.05O3, for example, showed degradation after 55 min in H-2 and 75 min in H-2/3%H2O atmospheres, with total disintegration of the sample soon after. The degradation, and hence loss in mechanical strength, was postulated as being due to reduction of the perovskite, because CoO was observed as a second phase. La0.7Sr0.3CrO3 showed no such degradation in the mechanical strength even after 10 days in H-2 at 1000 degrees C. Hence, the increased sinterability of cobalt addition on the B-site of La(Sr)CrO3 is offset by the reduction of stability (and mechanical properties) under either H-2 or H-2/3%H2O environments.