Hole-states in Li doped NiO: Doping dependence of Zhang-Rice spectral weight

Abstract

We report on structural evolution and a dynamical transfer of spectral weight as observed at O K-edge x-ray absorption (XA) spectra up on hole doping in LixNi1−xO (0 ≤ x ≤ 0.24). We find that, the unit cell of doped NiO evolves in a specific way up to an intermediate doping level (x=0.12) and then follows a different trend. A double peak structure (one is localized and other one being more delocalized) of low energy spectral weight (LESW) at O K-edge is identified and quantified. Normalized LESW is found to increase linearly with an effective doping concentration (∼ x/(1 − 2x)) with a change in slope at x=0.12, which is correlated to the observed structural evolution. Doping dependence of Ni L3-edge XA spectral shape closely follows the localized peak of LESW at O K-edge. Our observations strongly support the Zhang-Rice (ZR) picture, confirming doped holes in NiO are of primarily ZR character. Further, we find that Fe co-doping destroys ZR spectral weight and recovers the spectral shapes to that of NiO.