Solubility limits and LaGaO 3 compatibility in the LaO 1.5 ‐GaO 1.5 ‐NiO ternary system

Phase compatibility and solubility limits in the LaO 1.5 ‐GaO 1.5 ‐NiO system at 1400°C were measured using phase analysis and disappearing phase methods, focusing on compatibility of LaGaO 3 with NiO and La n +1 Ni n O 3 n +1 Ruddlesden‐Popper phases. For the first time, it was observed that, similar to La 4 Ni 3 O 10 , the incorporation of gallium stabilized La 3 Ni 2 O 7 over a narrow composition range. The compositional limits of stability involving LaGaO 3 were determined in detail, and the full quasiternary diagram is presented as a best estimation that is consistent with the observations of this study. LaGaO 3 showed compatibility with NiO, with gallium and nickel substituting for each other in both phases. The lowest attainable amount of nickel in LaGaO 3 in equilibrium with gallium‐saturated NiO was measured to be around 7% nickel on gallium sites. Of the Ruddlesden‐Popper phases, only La 4 Ni 3 O 10 showed compatibility with LaGaO 3 , with the two‐phase region spanning between ~40%‐55% gallium on nickel sites in La 4 Ni 3 O 10 and ~20%‐50% nickel on gallium sites in LaGaO 3 . The electrical conductivity of La 4 (Ni 1− x Ga x ) 3 O 10 was also measured, and found to decrease monotonically with the addition of gallium. Implications relating to fabrication of solid oxide fuel cells with Sr‐ and Mg‐doped LaGaO 3 electrolytes are discussed.