The La0.95Ni0.6Fe0.4O3-CeO2 system: Phase equilibria, crystal structure of components and transport properties

Phase equilibria, crystal structure, and transport properties in the (100-x) La0.95Ni0.6Fe0.4O3-xCeO2 (LNFCx) system (x=2-75 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 (R (3) over barc), the modified ceria with fluorite structure (Fm (3) over barm), and NiO as a secondary phase. These multiphase compositions exhibit metallic-like conductivity above 300 degrees 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 LNFCx (25 <= x <= 75) are more complicated. A change from semiconducting to metallic-like conductivity behavior was observed in LNFC25 at about 550 degrees C. The conductivity of LNFCx (25 <= x <= 75) could be explained in terms of a modified simple mixture model. (C) 2011 Elsevier Inc. All rights reserved.