Electronic conductivity of modified La_0.95Ni_0.6Fe_0.4O_3-δ perovskites

Phase composition and electronic conductivity of La_0.95Ni_0.6Fe_0.4O_3-δ (LNF) modified by small additions (2-10 mol%) of MnO₂, TiO₂, CeO₂ and Sr-containing manganese perovskite were investigated. A-site deficiency was found to be only limited in extent with typically NiO precipitates compensating for the nominal A-site deficiency. The phase composition of modified LNF varies depending on the type and amount of oxide additives. A low level of doping (∼2 mol%) does not change the value of conductivity and temperature of the semiconducting-metallic transition (∼300 °C). However, electronic conductivity of the modified LNF decreases if it contains 5 mol% of oxide additive or more. A decrease in conductivity was observed independently whether a secondary phase is present, solid solutions form or a change in symmetry of the modified LNF occurs. After reduction in argon atmosphere all compositions investigated exhibit semiconducting behaviour in a wide temperature range. Neutron powder diffraction measurements give insight into the mechanism of solid state interaction of LNF with small degrees of oxide additives.