Fig. 8: Structural distortions of nickel sites and their effects on the O K-edge XAS spectrum.

a Ideal NiO6 centre with well-defined eg and t2g orbitals and its corresponding transition from the O 1s states to hybridised O 2p-TM 3d orbitals. Occupied oxygen (metal) states are shown in red (blue). Empty states are given with striped colours. b Elongated tetragonal distortion, and square-based pyramid coordination of nickel sites. Splitting of eg and t2g gives rise to an additional feature in the O K-edge spectrum. Experimental NEXAFS spectra of O K-edge for NiFe0.3Ox and NiFe0.3MoOx are shown.