Double B mixed perovskite-type series in the La0.6Ca0.4Mn1−xCoxO3−δ system with x=0–1.0 was synthesized in air by solid state reactions at 1100°C from La2O3, MnO2, CoO simple oxides and CaCO3. Replacement of Mn cations by Co is characterized by U-shaped dependence of the conductivity versus Co content with a small maximum at x=0.3. Lower conductivities of the Co–Mn containing compositions compared to La0.6Ca0.4MnO3−δ and La0.6Ca0.4CoO3−δ are explained by stronger polarization of the double B ⋯–Mn(α+γ)+–Oα−–Co(α−γ)+–Oα−–⋯ fragments of the ⋯–Oα−–Mnα+–Oα−–Mnα+–Oα−–Mn(α+γ)+–Oα−–Co(α−γ)+–Oα−–⋯ chains in comparison with the single B ⋯–Oα−–Mnα+–Oα−–Mnα+–Oα−–⋯ and ⋯–Oα−–Coα+–Oα−–Coα+–Oα−–⋯ fragments, because of different electronegativity values of Co and Mn. The double exchange theory gives strong explanation for this phenomenon. Type and level of the electrical conductivity of the La0.6Ca0.4Mn1−xCoxO3−δ series are functions of the [Mn4+]/[Mn3+] and [Co3+]/[Co2+] ratios. Mn4+ and Co2+ cations are possible point defects which determinate the observed p- or n-type conductivity of the compositions, respectively.

Double B perovskite-type series in the system La0.6Ca0.4Mn1-xMexO3-delta with Me=Fe, Co, Ni and x=0-0.6 were synthesized in air by solid state reactions at 1200 degrees C from simple oxides and CaCO3. Almost single phase compositions with small impurities (3-5%) were formed. Replacement of Mn with Me-cations is accompanied by a considerable decrease of electrical conductivity of the prepared ceramics. Lower conductivities of the Me containing compositions compared to La0.6Ca0.4MnO3-delta are explained by stronger polarization of the -Mn(alpha + gamma)+-O alpha--Me(alpha-gamma)+-O alpha--fragments of the -O alpha--Mn alpha+ -O alpha--Mn alpha+ -O alpha--Mn(alpha+gamma)+ -O alpha-Me(alpha-gamma)+-O alpha--chains in comparison with the -O alpha--Mn alpha+-O alpha--Mn alpha+-O alpha- chains without Me-cations, because of different electronegativity of Me and Mn. The double exchange theory gives strong explanation for this phenomenon. Type and level of the electrical conductivity of the La0.6Ca0.4Mn1-xMexO3-delta series are the functions of the [Mn4+/[Mn3+] and [Me3+]/[Me2+] ratios. Mn4+ and Me2+ -cations are possible point defects which determine the p- and n-type conductivity of compositions, respectively. (c) 2008 Elsevier B.V. All rights reserved.