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 MPa⅐m 1/2 at room temperature and decrease to ϳ1 MPa⅐m 1/2 at temperatures >300°C. A decrease in fracture toughness is consistent with ferroelastic behavior, because the rhombohedral distortion decreases with increasing temperature.
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