Electrical conductivity dependence of Ni doped Sm0.95Ce0.05FeO3-δ on surface morphology and composition

Sm0.95Ce0.05Fe1-xNixO3-delta materials are considered as candidates for sensing reducing gases. The total electrical conductivity of Ni doped Sm0.95Ce0.05FeO3-delta perovskite materials is discussed in terms of Ni concentration, surface morphology and relative surface atomic ratios. Powders of formula Sm0.95Ce0.05Fe1-xNixO3-delta (x = 0-0.10) were prepared from citrate precursors by using a sol gel method and were then pressed uniaxially and sintered at 1350 degrees C for 4 h to form pellets. In fresh pellets the relative surface atomic ratios of Sm and Ni increased while that of Fe and Ce decreased as a function of nickel concentration, showing the segregation of samarium species. In contrast, the chemically reduced pellets show Fe rich surfaces. The electrical conductivity of fresh, partially reduced (700 degrees C under 5% (v/v) H-2/N-2 for 1 h) and fully reduced (1000 degrees C under 5% (v/v) H-2/N-2 for 1 h) pellets was measured by the four probe DC method. Under air, x = 0.07 and x = 0.10 showed the highest electrical conductivity in the series. Interestingly the x = 0.01-0.05 materials were n-type conductors while x = 0.07-0.10 exhibited p-type behaviour. The reduction treatment at 1000 degrees C enhanced electrical conductivities up to similar to 5000 fold due to changes associated with surface morphology and surface elemental composition. While phase separations are usually detrimental, in this case the reduced sensors are more sensitive without sacrificing reproducibility. (C) 2011 Elsevier B.V. All rights reserved.