Local Atomic Arrangement and Electronic Structure of Nanocrystalline Transition Metal Oxides Determined by X-ray Absorption Spectroscopy

摘要

The local crystal structure and electronic configuration of transition metal in X-ray amorphous MnO_2 and CrO_2 nanocrystals have been examined by using X-ray absorption (XAS) spectroscopy at Mn K and Cr K-edges. The Mn K-edge XAS study reveals that tetravalent manganese ions are stabilized in α-MnO_2-type local atomic arrangement consisting of the intergrowth of edge- and corner-shared MnO_6 octahedra. On the other hand, it is found from Cr K-edge XAS results that nanocrystalline CrO_2 possesses two different kinds of local structures around chromium, that is, Cr_2O_3-type with octahedral site and CrO_3-type with tetrahedral site. The presence of Cr~(+VI) species on the surface would be helpful for Li grafting process, giving rise to excellent electrochemical performances. This work can be regarded as a strong evidence for the usefulness of XAS to study nanocrystalline electrode materials.