Electronic structure and metal-insulator transition in LaNiO3-δ -: art. no. 155101

We studied the changes in the electronic structure of LaNiO3-delta across the metal-insulator transition. The technique used in the study was mainly O 1s x-ray absorption spectroscopy (XAS). The experimental spectrum of LaNiO3.00 was analyzed in terms of a cluster-model calculation. The spectrum of LaNiO3.00 presents a sharp peak at a threshold that corresponds to 3d(8)(L) under bar --> (C) under bar 3d(9) transitions. Analysis of this peak indicates that the charge carriers in LaNiO3.00 contain considerable oxygen character. The intensity of this peak decreases in the spectrum of LaNiO2.75 and disappears almost completely for LaNiO2.50. This suggests that the metal-insulator transition is related to the disappearance of the charge carriers and the ensuing band-gap opening. The peak in the LaNiO2.75 compound is split due to the presence of two nonequivalent crystallographic sites. The metal-insulator transition in this compound is tentatively attributed to potential disorder between these two sites.