The use of the oxygen Auger parameters in the characterisation of oxygen-containing compounds

Electronic relaxation phenomena play a key role in determining the chemical shift observed in photoemission and Auger transitions. The aim of this paper is to investigate the relaxation effects in oxygen-containing compounds by means of two oxygen Auger parameters α′=EB (1s) + EK (KL23L23; 1D) and β′ = EB (1s) + EK (KL1L23; 1P). It is shown that shifts of these Auger parameters with respect to the watermolecule in the gas phase can be related directly to the hole-hole repulsion energies U(2p2p) and U(2s2p), and they therefore contain very useful information on the nature of the chemical bonds involving oxygen. The hole-hole repulsion energy values are reduced with respect to the atomic or free ion values by screening and polarisation in the molecular or solid state. U(2p2p) values for high-Tc copper oxide superconductors are also of interest because these quantities are necessary to calculate the exchange and superexchange interactions between the O2p hole and the Cu3d9 spin, which are crucial to our understanding of the physics of these materials. Considering a large data set of oxygen-containing compounds we show that, (1) U(2p2p) (eV) ≈ 8.5 - Δα′ and U(2s2p) (eV) ≈ 16.5 - Δβ′ where the Auger parameter shifts are calculated with respect to H2O(g) with α′ (H2O(g)) = 1038.5 eV and β′ (H2O(g)) = 1014.5 eV, (2) Δα′ and Δβ′ are roughly linearly correlated, the slope being distinctive of compounds with similar chemical character (metal-oxygen or non-metal-oxygen bonds), (3) larger values of the Auger parameter shifts are obtained for compounds where the nearest-neighbour metal ions have high polarisability, as in the case of transition metal oxides and oxyanions.