Synthesis, characterization and redox behavior of nano-size La0.8Sr0.2Mn0.8Fe0.2O3-δ

Abstract

Nanosized crystallites of the mixed oxides LaMnO 3+x (LM), La 0.8 Sr 0.2 MnO 3-γ (LSM) and La 0.8 Sr 0.2 Mn 0.8 Fe 0.2 O 3-δ (LSMF) were synthesized by alternative methods like nitrate route, drip pyrolysis and ceramic route followed by calcinations at different temperatures. The average crystallite size of LSMF was found to be 10, 25 and 90 nm respectively for the calcinations temperatures of 700, 1150 and 1400 °C. The X-ray diffraction (XRD) studies showed that the LSMF sample calcined at 900 °C had orthorhombic symmetry which transforms to rhombohedral phase above 1150 °C and this high temperature phase was found to be stable up to 1400 C. Incorporation of iron into strontium-doped lanthanum manganite (LSM) was found to cause a structural rearrangement from rhombohedral to orthorhombic symmetry. The lattice parameters of these manganites were determined by indexing powder X-ray diffraction (XRD) patterns. From Mossbauer spectrum it was confirmed that only one kind of iron is present in an asymmetric environment. Temperature programmed reduction (TPR) results indicated that (i) above systems contains Mn in +3 and +4 oxidation states, (ii) Fe reduces at lower temperature as compared to Mn 4+ in rhombohedal LSMF and (iii) Fe 3+ and Mn 4+ undergo simultaneous reduction in orthorhombic LSMF phase.