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

Phase composition and electronic conductivity of La0.95Ni0.6Fe0.4O3-delta (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 (similar to 2 mol%) does not change the value of conductivity and temperature of the semiconducting-metallic transition (similar to 300 degrees 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 ora 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. (C) 2008 Elsevier B.V. All rights reserved.