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 unloading, and a mechanism related to ferroelastic domain switching in the rhombohedral perovskite is proposed. Domain switching in the materia ls has been confirmed using X-ray diffractometry. Fracture toughnesses of L a0.8Ca0.2CoO3 measured using single-edge notched beam and single-edge V-not ched beam methods coincide and are equal to 2.2 MPa(.)m(1/2) at room temper ature and decrease to similar to 1 MPa(.)m(1/2) at temperatures > 300 degre esC. A decrease in fracture toughness is consistent with ferroelastic behav ior, because the rhombohedral distortion decreases with increasing temperat ure.