Solubility limits and LaGaO3 compatibility in the LaO1.5-GaO1.5-NiO ternary system

Phase compatibility and solubility limits in the LaO1.5-GaO1.5-NiO system at 1400 degrees C were measured using phase analysis and disappearing phase methods, focusing on compatibility of LaGaO3 with NiO and Lan+1NinO3n+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 similar to 40%-55% gallium on nickel sites in La4Ni3O10 and similar to 20%-50% nickel on gallium sites in LaGaO3. The electrical conductivity of La-4(Ni1-xGax)(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 LaGaO3 electrolytes are discussed.