Electrical conduction mechanism of LaNi_xMe_1−xO_3−δ (Me = Fe, Mn)

Graphical abstract: Compositional dependence of (a) electrical conductivity and (b) E_a for hopping conduction of LaNi_xMe_1−xO₃ (Me = Fe, Mn). - Highlights: • Electrical conduction mechanism of LaNi_xMe_1−xO₃ (Me = Fe, Mn) was investigated. • Hopping conduction model could be applied for conductivity of both specimens. • The difference of E_a due to that of energy level of Fe and Mn was observed. • Hole concentration estimated by iodimetry increases with increasing Ni content. - Abstract: Electrical conduction mechanism of LaNi_xFe_1−xO_3−δ and LaNi_xMn_1−xO_3+δ expected as Sr-free new cathode material for solid oxide fuel cells was analyzed. Electrical conduction behaviors of both specimens could be well fitted by small polaron hopping conduction model. The electrical conductivity of LaNi_xFe_1−xO_3−δ increased with increasing Ni content, showing agreement with decrease of activation energy for hopping conduction. The decrease of electrical conductivity and increase of activation energy of LaNi_xMn_1−xO_3+δ were observed with increasing Ni content for 0.0 ≤ x ≤ 0.4. Further Ni substitution increased electrical conductivity and decreased activation energy for 0.4 ≤ x ≤ 0.6. It was revealed using iodometry that the difference of hole carrier density between LaNi_xFe_1−xO_3−δ and LaNi_xMn_1−xO_3+δ was small. It was suspected that the origin of the difference of electrical conduction behavior of LaNi_xFe_1−xO_3−δ and LaNi_xMn_1-xO_3+δ was difference of energy level of e_g band composed of Fe 3d or Mn 3d orbitals and their overlapping quantity with O 2p and Ni 3d band