THE FINE-STRUCTURE OF THE CU2P3/2 X-RAY PHOTOELECTRON-SPECTRA OF COPPER-OXIDE BASED COMPOUNDS

This paper shows that in copper oxide based compounds where Cu ions are in a square planar geometry with four coordination oxygen ions, i.e. CuO and NdCuO4, the Cu2p3/2 ((3d)10L) X-ray photoelectron core lines are narrower than in similar compounds with Cu ions in a pyramidal or octahedral geometry with five or six neighboring oxygens, i.e. Bi2Sr2CaCU2O8 and La2CUO4. To explain this difference two different charge transfer mechanisms from the oxygen p orbitals to the Cu3d orbitals are proposed. For square planar geometry (CUO4) only the px,y--> dx2 -y2 charge transfer is allowed, whereas for octahedral or pyramidal geometry the additional pz--> dz2 transition could take place. These two different final state configurations will produce different ionization potentials for the Cu2P3/2 core levels.