Ferroelastic Behavior of LaCoO 3 ‐Based Ceramics

LaCoO 3 and La 0.8 Ca 0.2 CoO 3 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 unloading, 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 diffractometry. Fracture toughnesses of La 0.8 Ca 0.2 CoO 3 measured using single‐edge notched beam and single‐edge V‐notched beam methods coincide and are equal to 2.2 MPa·m 1/2 at room temperature and decrease to ∼1 MPa·m 1/2 at temperatures >300°C. A decrease in fracture toughness is consistent with ferroelastic behavior, because the rhombohedral distortion decreases with increasing temperature.