Analysis of electrical conduction mechanism of LaNi_1-xMe _xO_3-δ (Me = Fe, Mn)

Electrical conduction mechanism of LaNi_1-xFe_xO _3-δ and LaNi_1-xMn_xO_3+δ, which are expected as Sr-free new cathode material for solid oxide fuel cells, was analyzed using electrical conductivity measurements at high temperatures. Electrical conduction behaviors of both specimens can be well fitted into small polaron hopping conduction model. The electrical conductivity of LaNi _1-xFe_xO_3-δ increased with increasing Ni content, showing agreement with decrease of activation energy for hopping conduction. Almost constant activation energy irrespective of sintering temperature indicated that observed activation energy can be attributed to intraparticle conduction. The decrease of electrical conductivity and increase of activation energy of LaNi_1-xMn_xO_3+δ were observed with increasing Ni content for 0.6≥x≥1.0. Further Ni substitution increased electrical conductivity and decreased activation energy for 0.4≥x≥0.6. It can be suspected that the origin of the difference of electrical conduction behavior of LaNi_1-xFe_xO _3-δ and LaNi_1-xMn_xO_3+δ is difference of energy level of eg band composed of Fe 3d or Mn 3d orbitals and their overlapping quantity with O 2p and Ni 3d band.