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

摘要

A structural study has been performed on the La_(0.8)Sr_(0.2)Fe_xCo_(1-x)O_3 (x = 0.025 to 0.3) system displaying large magnetoresistance (MR) at room temperature. 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 superreflections in the corresponding SAED patterns revealed that a superstructure is formed due to the presence of iron. The correlation between the ordered microstructure and the observed large MR ratio is discussed. ~(57)Fe 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 La_(0.8)Sr_(0.2)Fe_2Co_(1-x)O_3 compounds were found to increase monotonously with increasing Fe content. The valence state of iron was found to be Fe~(3+).