Structure and properties of La_0.4Sr_0.4TiO₃ Ceramics for use as anode materials in solid oxide fuel cells

In this work, La_0.4Sr_0.4TiO₃-based ceramics intended for use as anode materials in solid oxide fuel cells were investigated. The material was found to preserve its cubic structure throughout testing across a range of conditions, although slight signs of phase segregation were also identified under extreme conditions. The thermal expansion coefficient measured on differently processed samples predicts a good thermomechanical compatibility with yttria-stabilized zirconia (YSZ). Conductivity measurements indicated that the material exhibits a fast surface reduction, unlike the bulk reduction, which progresses very slowly. An increase of the prereduction temperature was found to significantly increase the extent of the reduction and, therefore, the conductivity. Samples sintered under a 5% H₂/Ar flow, at 1400 °C, showed high conductivities of up to 96 S cm^-1 at 880 °C and oxygen partial pressures of pO₂ = 10^-20 atm. Correlations between the oxygen deficiency, conductivity, porosity, reduction temperature, and cell parameter are also presented. An equation that accounts for the expansion of the cell parameter on reduction has been adapted from the literature and is discussed.