Ferroelastic Behavior of LaCoO3-Based Ceramics

LaCoO3 and La0.8Ca0.2CoO3 ceramics show a nonelastic stress–strain behavior during four-point bending experiments where hysteresis loops are observed during loading–unloading cycles. Permanent strain is stored in the material after unload-ing, and a mechanism related to ferroelastic domain switching in the rhombohedral perovskite is proposed. Domain switching in the materials has been confirmed using X-ray diffractom-etry. Fracture toughnesses of La0.8Ca0.2CoO3 measured using single-edge notched beam and single-edge V-notched beam methods coincide and are equal to 2.2 MPam1/2 at room temperature and decrease to 1 MPam1/2 at temperatures>300°C. A decrease in fracture toughness is consistent with ferroelastic behavior, because the rhombohedral distortion decreases with increasing temperature. I