The electronic structure of the doped one-dimensional transition metal oxide Y2-xCaxBaNiO5 studied using X-ray absorption

A strong anisotropic distribution of the holes in Ni 3d and O 2p orbitals is observed in the polarization dependent O 1s and Ni 2p(3/2) X-ray absorption spectroscopy of the linear-chain nickelate Y2-xCaxBaNiO5 (x = 0, 0 05, 0.1, 0.2), which demonstrates the one-dimensional nature of the electronic state in these compounds. The holes introduced by Ca-doping occupy both O 2p and Ni 3d orbitals along the NiO5 chains. By comparing the experimental Ni 2p(3/2) absorption spectra of Y2-xCaxBaNiO5 to those from charge transfer multiplet calculations we can derive the orbital character of the additional holes to be of similar to60% O2p and similar to40% Ni 3d.