Investigation of the quasi-ternary system LaMnO 3–LaCoO 3–“LaCuO 3”—I: the series La(Mn 0.5Co 0.5) 1 −xCu xO 3 −δ

Abstract

The La(Mn 0.5Co 0.5) 1 −x Cu x O 3 −δ series with x=0, 0.05, 0.1, 0.2, 0.4, 0.6, 0.8 and 1 was synthesized by the Pechini method to obtain insight into the phase formation in the quasi-ternary LaMnO 3–LaCoO 3–“LaCuO 3” system caused by the instability of LaCuO 3 under ambient conditions. After sintering at 1100°C some remarkable results were obtained: LaMn 0.3Co 0.3Cu 0.4O 3 −δ crystallized as a single phase in the orthorhombic perovskite structure typical of LaCuO 3. Among the synthesized compositions this compound showed the highest electrical conductivity in air at 800°C (155 S cm −1) and also the highest thermal expansion coefficient ( α 30−800°C=15.4×10 −6 K −1). The LaCuO 3 −δ composition also crystallized as a single phase but in a monoclinic structure although previous investigations have shown that other phases are preferably formed after sintering at 1100°C. The electrical conductivity and thermal expansion coefficient were the lowest within the series of compositions, i.e. 9.4 S cm −1 and 11.9×10 −6 K −1, respectively.