CONTRASTING BEHAVIOR OF HOMOVALENT-SUBSTITUTED AND HOLE DOPED-SYSTEMS- O-K-EDGE SPECTRA FROM LANI1-XMXO3 (M=MN, FE, AND CO) AND LA1-XSRXMNO3

We report x-ray absorption spectra at the oxygen K edge for LaNi1-xMxO 3 (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., a s in La1-xSrxMnO3 where states are formed within the band gap of the u nderlying electronic structure. The sensitivity of the O K-edge spectr a to substitution confirms the large oxygen 2p admixture to states at the Fermi level due to a substantial hopping interaction strength betw een the transition-metal 3d and oxygen 2p derived states in these pero vskite oxides. The present results suggest that the electronic structu res of these perovskite oxides are dominated by local interactions.