Mechanical behavior and electrical conductivity of La 1− xCa xCoO 3 ( x = 0, 0.2, 0.4, 0.55) perovskites

Abstract

This paper compares the important mechanical properties and the electrical conductivities from room temperature to 800 °C of four LaCoO 3 based cobaltite compositions with 0, 20, 40 and 55% Ca 2+ ions substituted on the A site of the perovskite structure respectively. Ca 2+ doped lanthanum cobaltite materials are strong candidates for use as cathodes in lower temperature solid oxide fuel cells operating at or below 800 °C. Among these four cobaltite compositions, two (LaCoO 3 and La 0.8Ca 0.2CoO 3) were found to be phase pure materials, whereas the remaining two compositions (La 0.6Ca 0.4CoO 3 and La 0.45Ca 0.55CoO 3) contained precipitation of secondary phases such as CaO and Co 3O 4. The mechanical properties of the four compositions, in terms of Young's modulus, four-point bending strength and fracture toughness measurements, were measured at both room temperature and 800 °C. At room temperature, doping with Ca 2+ was found to substantially increase the mechanical properties of the cobaltites, whereas at 800 °C the pure LaCoO 3 composition exhibited higher modulus and strength values than La 0.8Ca 0.2CoO 3. All of the four compositions exhibited ferroelastic behavior, as shown by the hysteresis loops generated during uniaxial load–unload compression tests. Electrical conductivity measurements showed the La 0.8Ca 0.2CoO 3 composition to have the highest conductivity among the four compositions.