Defect formation and mechanical stability of perovskites based on LaCrO3 for solid oxide fuel cells (SOFC)

Perovskites on the basis of LaCrO₃ are of interest as ceramic interconnect materials for the development of solid oxide fuel cells (SOFCs). The interconnects are exposed to oxidising and reducing atmospheres under operating conditions. Oxygen vacancy formation was determined as a function of oxygen partial pressure between 1 and 10^?22 bar at temperatures between 900 and 1100 °C. Different perovskite compositions made of (La,Ca/Sr)CrO_3?δ, La(Cr,Mg)O_3?δ, La(Cr,Mg/Cu/Co,Al)O_3?δ, and (La,Ca)(Cr,Al)O_3?δ were investigated. Defect models were evaluated to describe the oxygen vacancy formation and the respective thermodynamic data were determined. The results are used to explain existing literature data on the isothermal expansion of LaCrO₃ based perovskites under reducing conditions. Complementary mechanical measurements with selected perovskite compositions revealed that lower oxygen partial pressure causes higher stiffness, strength and fracture toughness. The change in properties is discussed in terms of the observed ferroelastic domains and the interaction of the domain wall motion with the oxygen vacancies.