Electronic and Magnetic Properties of Co3O4 and Co3–xNixO4 from DFT-Based Simulations of XANES Spectra at the Co K-Edge

Abstract

We present theoretical X-ray absorption near-edge structure (XANES) spectroscopy at the Co K-edge, combined with DFT + U calculations, to investigate the electronic and magnetic properties of Co₃O₄ normal spinel and the nickel-doped system Co_3–xNi_xO₄. Two configurations have been considered for the nickel-doped system: the configurations in which one nickel atom substitutes a tetrahedral and an octahedral cobalt, respectively. We found that Ni dopant prefers to occupy a tetrahedral site. The Co K-edge XANES spectrum shows two prepeaks in Co₃O₄ normal spinel, while only one prepeak is observed in the cases of doped systems. We attribute the disappearance of one prepeak in the doped systems to the shift toward high energies of tetrahedral cobalt 3d empty states. We demonstrated that nickel doping causes the oxidation state of tetrahedral cobalt to increase slightly while that of octahedral cobalt remains almost unchanged. Moreover, nickel possesses a magnetization when substituting octahedral cobalt and contributes to render Co₃O₄ a half metal system, while this magnetization decreases when nickel substitutes a tetrahedral cobalt.