XANES study on Ruddlesden-Popper phase, La_n+1Ni_nO_3n+1 (n = 1, 2, and ∞)

Ruddlesden-Popper phase, La_n+1Ni_nO_3n+1 (n = 1, 2 and ∞) compounds were prepared by citrate sol-gel method. We revealed the origin of the variation of the electrical conductivities in La_n+1Ni_nO_3n+1 (n = 1, 2 and ∞) using resistivity measurements, Rietveld analysis, and X-ray absorption spectroscopy. According to the XANES spectra, it is found that the degree of 4p_π - 4p_σ 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 4p_π - 4p_σ 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.