Crystal structure, thermochemical stability, electrical and magnetic properties of the two-phase composites in the La_0.8Sr_0.2MnO_{3 ± δ}-CeO₂ system

Crystal structure, thermochemical stability, transport and magnetic properties of compositions in the (100-x) La_0.8Sr_0.2MnO_{3 ± δ} xCeO₂ (LSMC) system were studied. All compositions in the LSMC series containing more than 2 mol% CeO₂ were two phase and consisted of the modified perovskite constituent with rhombohedral structure (R3̄c) and ceria as a secondary phase with cubic structure (Fm3̄m). The presence of both Ce⁴⁺and Ce³⁺ cations in LSMC compositions was revealed by X-ray Photoelectron Spectroscopy (XPS). CeO₂ and compositions in the LSMC series showed good thermochemical stability in air and argon. However, in H₂-Ar atmosphere all LSMC compositions underwent reduction followed by decomposition. Transport and magnetic properties change in a non-linear way with the increase in the CeO₂ content. The LSMC2 composition showed enhanced electronic conductivity and magnetic characteristics. Metallic type conductivity was observed for LSMC compositions with x ≤ 36 mol% CeO₂ in a narrow temperature range of 770-900 °C. A small degree of substitution of Ce into LSM was found to change structural, magnetic and electrical properties.