B23-P-06Local electronic structure Analysis for brownmillerite CaFeMnO2.5

Abstract

The brownmillerite structure (ABB'O 2.5 ) is a typical example of a layered structure with anion vacancy ordering. It consists of alternate layers of BO 4 tetrahedra and B'O 6 octahedra. Interestingly, there is the preference for B site metals to occupy in tetrahedral or octahedral sites. In the case of CaFeMnO 2.5 , Mn ions preferentially occupy the octahedral site. However, it is known that Fe and Mn ions are not fully ordered but low amount of Fe (Mn) resides in octahedral (tetrahedral) site [ 1 , 2 ]. In general, it is difficult to empirically extract the information about the individual octahedral and tetrahedral site using X-ray absorption spectroscopy. In contrast, atomically Figure1: Brownmillerite structure resolved electron energy loss spectroscopy (EELS) by scanning transmission electron microscopy (STEM) can extract such information. In the present research, Fe and Mn L 2,3 -edge were measured at octahedral and tetrahedral sites in CaFeMnO 2.5 using Dual-EELS technique. The observed spectra show not only differences of spectral fine structure but also small chemical shift depending on local electronic structure.