Contrasting behavior of homovalent-substituted and hole-doped systems: O K-edge spectra from LaNi_1−xM_xO₃ (M=Mn, Fe, and Co) and La_1−xSr_xMnO₃

Abstract

We report x-ray-absorption spectra at the oxygen K edge for LaNi_1−xM_xO₃ (M=Mn, Fe, and Co) for values of x spanning the entire composition range which exhibit metal-insulator transitions at critical values of x. This study clearly shows that the metal-insulator transition in the homovalent substituted series is achieved by transferring hole states from near E_F to an energy position above E_F due to the potential of the substituent. This is in strong contrast to hole doping, e.g., as in La_1−xSr_xMnO₃, where states are formed within the band gap of the underlying electronic structure. The sensitivity of the O K-edge spectra to substitution confirms the large oxygen 2p admixture to states at the Fermi level due to a substantial hopping interaction strength between the transition-metal 3d and oxygen 2p derived states in these perovskite oxides. The present results suggest that the electronic structures of these perovskite oxides are dominated by local interactions.