Solubility limits and LaGaO₃ 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 LaGaO₃ with NiO and La_n+1Ni_nO_3n+1 Ruddlesden-Popper phases. For the first time, it was observed that, similar to La₄Ni₃O₁₀, the incorporation of gallium stabilized La₃Ni₂O₇ over a narrow composition range. The compositional limits of stability involving LaGaO₃ were determined in detail, and the full quasiternary diagram is presented as a best estimation that is consistent with the observations of this study. LaGaO₃ showed compatibility with NiO, with gallium and nickel substituting for each other in both phases. The lowest attainable amount of nickel in LaGaO₃ in equilibrium with gallium-saturated NiO was measured to be around 7% nickel on gallium sites. Of the Ruddlesden-Popper phases, only La₄Ni₃O₁₀ showed compatibility with LaGaO₃, with the two-phase region spanning between ~40%-55% gallium on nickel sites in La₄Ni₃O₁₀ and ~20%-50% nickel on gallium sites in LaGaO₃. The electrical conductivity of La₄(Ni_1−xGa_x)₃O₁₀ 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 LaGaO₃ electrolytes are discussed.