Structural features of the La-Sr-Fe-Co-O system

A structural study has been performed on the La0.8Sr0.2FexCo1-xO3 (x = 0.02 5 to 0.3) system displaying large magnetoresistance (MR) at room temperatur e. A detailed analysis of the crystal structure and microstructure was done by X-ray diffraction (XRD), transmission and scanning electron microscopy (TEM and SEM). The atomic resolution TEM images and the appearing superrefl ections in the corresponding SAED patterns revealed that a superstructure i s formed due to the presence of iron. The correlation between the ordered m icrostructure and the observed large MR ratio is discussed. Fe-57 Mossbauer spectroscopy was utilized to gain information on the valence state of iron in the sample with x = 0.3. The lattice parameters of Fe- doped La0.8Sr0.2 FexCol- xO3 compounds were found to increase monotonously with increasing F e content. The valence state of iron was found to be Fe3+.