High temperature oxygen NEXAFS valence band spectra and conductivity of   LaFe3/4Ni1/4O3 from 300 K to 773 K
  LaFe3/4Ni1/4O3 was subjected to oxygen near edge x-ray absorption fine structure (NEXAFS) spectroscopy for 300 K < T < 773 K. The spectra show in the pre-edge a small hole doped peak originating from Ni substitution. The relative spectral weight of this transition to the weight of the hybridized O(2p) - Fe(3d) transitions scales with T and has a maximum at around 600 K. The characteristic energies of the thermal activated spectral intensity and conductivity suggest that the concentration of charge transferred electrons from O(2p) to Ni(3d) increases and that the pre-edges account in part for the polaron activated transport. 
Artur Braun, Selma Erat, Ahmad K. Ariffin, Recardo Manzke, Hiroki   Wadati, Thomas Graule, Ludwig J. Gauckler
cond-mat.str-el