THERMODYNAMIC ANALYSIS OF REACTION PROFILES BETWEEN LAMO3 (M=NI,CO,MN) AND ZRO2

Chemical reactions of LaMO3(M = Ni, Co, Mn) and ZrO2 have been analyzed using chemical potential diagrams for the La-Zr-M-O systems under a condition of P(O2) = 1 bar. A log{a(M)/a(Zr)} vs. log{a(La)/a(Zr)} plot is appropriate for representing diffusion paths, because the layered arrangement of the reaction zone corresponds well to the geometrical configuration of stability polygons of reactants (LaMO3 and ZrO2) and products (La2Zr2O7, MO, La2ZrMO6, etc.). A complicated arrangement including a ternary perovskite phase, La2ZrNiO6, observed in the La2NiO4/YSZ couple can be represented by a simple diffusion path having the same slope in the chemical potential diagram as in the LaCoO3/YSZ couple. The effect of lanthanum nonstoichiometry for La(y)MnO3 has been discussed in relation to La2Zr2O7 formation and manganese dissolution into YSZ cubic phases.