On the electronic structure of Cu (III) and Ni (III) in La2 Li½ Cu½ O4, Nd2 Li½ Ni½ O4, and Cs2 KCuF6

Abstract

The electronic structure of copper and nickel in the oxidation state +III was studied for La2 Li½ Cu½ O4 , Cs2 KCuF6 , and Nd2 Li½ Ni½ O4 by X-ray absorption near-edge structure (XANES) spectroscopy at the L2,3 -thresholds of Cu and Ni as well as the K-thresholds of O and F. The observed multiplet structures are well described by cluster configuration-interac-tion calculations, which result in a high-spin ground state for Cs2 KCuF6 and low-spin ground states for La2 Li½ Cu½ O4 and Nd2 Li½ Ni½ O4 . The simulations yielded 30% and 40% 3d^8 contributions for La2 Li½ Cu½ O4 and Cs2 KCuF6 , respectively, and 57% 3d^7 for Nd2 Li½ Ni½ O4 in the ground state. The O--K and F--K XANES spectra exhibit pronounced preedge peaks that monitor ligand--2p holes induced by covalency. These preedge peaks move to lower energies with increasing oxidation state of Cu and Ni as well as when going from nickelates to cuprates. B.V. All rights reserved.