Oxide-ion solid electrolytes made from strontium and magnesium doped LaGaO3 (LSGM) equipped with Ni-cermet anodes and La1‑xSrxCo1‑yFeyO3 perovskite cathodes are considered as promising materials selection for solid oxide fuel cells working at intermediate temperatures, 500 - 700 °C (IT-SOFC).
Knowledge of phase equilibria in the chemical systems, which represent cathode, solid electrolyte and anode as well as their possible combinations, is essential for the successful fabrication and exploitation of IT-SOFC. The thermodynamic stability of the electrolyte and electrodes themselves as well as the reactivity between the electrolyte and electrodes can be expressed numerically in the chemical potential diagrams. With regard to LSGM ceramics and Ni, thermodynamic database for the system La-Sr-Ga-Mg-Ni-O is required.
In this paper, we present the result of thermodynamic analysis for the systems La-Ga-O, La‑Mg-O, Ga-Mg-O, La-Ni-O, Ga-Ni-O, Sr-Ni-O, La-Ga-Mg-O, and La-Ga-Ni-O. Thermodynamic functions of the ternary LaGaO3, La4Ga2O9, La2NiO4, La3Ni2O7, La4Ni3O10, LaNiO3, Ga2NiO4, and Ga2MgO4 compounds have been evaluated. Calculations of the chemical potential diagrams for the La-Ga-Ni-O system show that LaGaO3 is always stable in contact with NiO, while it reacts with La2NiO4, La3Ni2O7, and La4Ni3O10 to form La4Ga2O9 and NiO. At the same time, LaNiO3 and LaGaO3 may coexist in a range of temperatures and oxygen partial pressures.
Complementary experimental studies have been undertaken to determine phase equilibria in the Sr-Ni-O system for the first time and to check the topology of the isothermal sections La2O3-Ga2O3-MgO and La2O3-Ga2O3-NiO against the results of thermodynamic calculations based on assessed systems La-Ga-O, La-Mg-O, Ga-Mg-O, La-Ni-O, and Ga-Ni-O.
E-mail: zinkevich@mf.mpg.de