The La_0.95Ni_0.6Fe_0.4O₃CeO ₂ system: Phase equilibria, crystal structure of components and transport properties

Phase equilibria, crystal structure, and transport properties in the (100-x) La_0.95Ni_0.6Fe_0.4O₃xCeO ₂ (LNFCx) system (x=275 mol%) were studied in air. Evolution of phase compositions and crystal structure of components was observed. The LNFCx (2≤x≤10) are three-phase and comprise the perovskite phase with rhombohedral symmetry (R3c), the modified ceria with fluorite structure (Fm3m), and NiO as a secondary phase. These multiphase compositions exhibit metallic-like conductivity above 300 °C. Their conductivity gradually decreases from 395.6 to 260.6 S/cm, whereas the activation energy remains the same (E_a=0.040.05 eV), implying the decrease in the concentration of charge carriers. Phase compositions in the LNFCx (25≤x≤75) are more complicated. A change from semiconducting to metallic-like conductivity behavior was observed in LNFC25 at about 550 °C. The conductivity of LNFCx (25≤x≤75) could be explained in terms of a modified simple mixture model.