1s3p Resonant Inelastic X-ray Scattering of Cobalt Oxides and Sulfides

We are developing 1s3p resonant inelastic X-ray scattering (RIXS) as a versatile spectroscopic tool to probe active systems under working conditions. In order to establish detailed reference materials for cobalt-based systems, we have applied 1s X-ray absorption spectroscopy (XAS) and 1s3p RIXS to cobalt oxides (CoO, Co3O4) and sulfides (CoS and CoS2). We show that the Co3+ ions in Co3O4 contain a large nonlocal peak intensity in the pre-edge and that the resonant 3p final state of Co3O4 is dominated by the two exchange-split peaks of the tetrahedral Co2+ site. In contrast, the 3p final state of CoS and CoS2 shows a single asymmetric peak due to the large screening of the 3p-3d exchange interaction. While CoS has a single pre-edge peak, CoS2 contains an additional large nonlocal peak. This indicates that although CoS2 is often indicated as Co2+(S2)2-, it has a very strong sulfur-mediated cobalt-cobalt bonding, similar to the low-spin Co3+ sites in oxides. These electronic structure details reveal the significance of 1s3p RIXS spectroscopy for determining the symmetry, spin and covalence of transition metal compounds, information that is largely inaccessible in conventional K edge XAS. The experimental results are simulated with multiplet calculations that reveal the partial screening of the 3p3d exchange interaction and the presence of nonlocal transitions. We conclude that 1s3p RIXS combined with spectral simulations presents a valuable tool to unravel the electronic properties of functional materials under working conditions.