Mechanical properties of LaCoO3 based ceramics

Mechanical characteristics of LaCoO3 based ceramics have been measured over the temperature range from room temperature (RT) to 850 degrees C. The bending strength is in the range of 53 MPa for 83% dense LaCoO3, 76 MPa for 90% dense La0.8Sr0.2CoO3, and 150 MPa for 99% dense La0.8Ca0.2CoO3 ceramics at RT. The strength of LaCoO3 and La0.8Sr0.2CoO3 was relatively independent of temperature up to 850 degrees C. The strength of the dense La0.8Ca0.2CoO3 material decreased linearly to 850 degrees C, where the strength at 850 degrees C is only about 50% of the strength at RT. The fracture mode of this material is changed from fully transgranular at RT to mixed trans- and intergranular at 850 degrees C. Hardness in the range of 7-9 GPa for 90% dense La0.8Sr0.2CoO3 and 9-11 GPa for fully dense La0.8Ca0.2CoO3 ceramics have been observed. The fracture toughness is calculated to be 0.73 +/- 0.08 MPa m(1/2) for 90% dense La0.8Sr0.2CoO3, and 0.98 +/- 0.09 MPa m(1/2) for fully dense La0.8Ca0.2CoO3 ceramics. Young's modulus for dense La0.8Ca0.2CoO3 was measured to be 112+/-3 GPa. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.