ON THE NONLOCAL SCREENING MECHANISMS IN THE 2P PHOTOELECTRON-SPECTRA OF NIO AND LA2NIO4

An unresolved question in solid state physics concerns the nature of c harge transfer mechanisms in the late transition metal compounds. This paper shows that a structure similar to the doubly peaked feature det ected in the Ni 2p X-ray photoelectron spectra of NiO and attributed t o non-local screening is observed also in the Ni 3s spectrum. However, in this case the spectrum is fully accounted for on the basis of char ge transfer, near degeneracy, and exchange mechanisms and neglecting n on-local screening. In addition, it is demonstrated that non-local scr eening mechanisms are not observed in La2NiO4 where such an effect, on the basis of the Ni-O octahedra network, is expected. Finally, the si gnificant differences among the Ni 2p XPS spectra in NiO, Ni0.1Mg0.9O and La2NiO4 suggest that core line spectra in nickel oxide based compo unds cannot be evaluated simply on the basis of the Ni-O cluster netwo rk but it is necessary to consider the long range crystal structure ef fects. (C) 1997 Published by Elsevier Science Ltd.