Mechanical behavior and electrical conductivity of La_1-xCa_xCoO₃ (x = 0, 0.2, 0.4, 0.55) perovskites

This paper compares the important mechanical properties and the electrical conductivities from room temperature to 800 °C of four LaCoO₃ based cobaltite compositions with 0, 20, 40 and 55% Ca²⁺ ions substituted on the A site of the perovskite structure respectively. Ca²⁺ 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 (LaCoO₃ and La_0.8Ca_0.2CoO₃) were found to be phase pure materials, whereas the remaining two compositions (La_0.6Ca_0.4CoO₃ and La_0.45Ca_0.55CoO₃) contained precipitation of secondary phases such as CaO and Co₃O₄. 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 Ca²⁺ was found to substantially increase the mechanical properties of the cobaltites, whereas at 800 °C the pure LaCoO₃ composition exhibited higher modulus and strength values than La_0.8Ca_0.2CoO₃. 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_0.2CoO₃ composition to have the highest conductivity among the four compositions.