XANES study on Ruddlesden-Popper phase, Lan+1NinO3n+1 (n = 1, 2 and infinity )

Ruddlesden-Popper phase, Lan+1NinO3n+1 (n=1, 2, and infinity ) compounds were prepared by citrate sol-gel method. We revealed the origin of the variation of the electrical conductivities in Lan+1NinO3n+1 (n=1, 2, and infinity ) using resistivity measurements, Rietveld analysis, and X-ray absorption spectroscopy. According to the XANES spectra, it is found that the degree of 4pπ - 4pσ energy splitting between 8345 eV and 8350 eV is qualitatively proportional to the elongation of the out-of-plane Ni-O bond length. With the decrease of 4pπ - 4pσ splitting, the strong hybridization of the σ-bonding between Ni-3d and O-2p orbitals creates narrow antibonding σ* bands, which finally results in the lower electrical resistivity.