The La 0.95Ni 0.6Fe 0.4O 3–CeO 2 system: Phase equilibria, crystal structure of components and transport properties

Abstract

Phase equilibria, crystal structure, and transport properties in the (100 −x) La 0.95Ni 0.6Fe 0.4O 3– xCeO 2 (LNFC x) system ( x=2–75 mol%) were studied in air. Evolution of phase compositions and crystal structure of components was observed. The LNFC x (2≤ x≤10) are three-phase and comprise the perovskite phase with rhombohedral symmetry ( R3̄ c), the modified ceria with fluorite structure ( Fm3̄ m), 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 =0.04–0.05 eV), implying the decrease in the concentration of charge carriers. Phase compositions in the LNFC x (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 LNFC x (25≤ x≤75) could be explained in terms of a modified simple mixture model.