Synthesis, crystal stability, and electrical behaviors of La _(0.7)Sr _(0.3)Cr _(0.4)Mn _(0.6)O _(3-δ)-XCu _(0.75)Ni _(0.25) for its possible application as SOFC anode

摘要

La _(0.7)Sr _(0.3)Cr _(0.4)Mn _(0.6)O _(3-δ) (perovskite-type) nanocomposites impregnated with XCu _(0.75)Ni _(0.25) have been synthesized by sol-gel method. Crystal structure of LSCM-Cu _(0.75)Ni _(0.25) composites were refined by the Rietveld method. Crystal symmetry of CuO and NiO nanoparticles have monoclinic C12/c and cubic Fm3?m symmetry, respectively, but after sintering at 1,200 °C and reducing the temperature to 600 °C, it's transformed into a new Cu _(0.75)Ni _(0.25) intermetallic solid solution without secondary phase. We have detected a cationic inter-diffusion in Cu ? Ni interphase crystals during this reduction process; however, when sintering time exceeds 2 h at 1,200 °C this reaction mechanism is interrupted by a sublimation phenomenon; which causes Cu 2O cubic structure segregation from monoclinic CuO structure. This leads to Cu precipitation from the Cu 1-xNi x solid solution. Cu _(0.75)Ni _(0.25) inhibits the LSCM perovskite-type grain growth (? 220 nm). Electrical conductivity indicates the presence of semiconductor and metallic-type behaviors with a maximum electrical conductivity (800 °C)>4.5 (log r, Sm cm -1). When Cu _(0.75)Ni_0.25)concentration was 25 and 35 %, semiconductor behavior were dominated. Thermal expansion coefficients showed a linear dependence inversely proportional to Cu _(0.75)Ni _(0.25)concentration. Electrical conductivity, Rietveld analysis, Porosity, TEC, and Ea behaviors lead to the conclusion that the anodes between 25 and 35 % (Cu _(0.75)Ni _(0.25)) are closer to applications at SOFC.