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

Abstract

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′= E B (1s) + E K ( KL 23 L 23; 1D) and β′ = E B (1s) + E K ( KL 1 L 23; 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- T c 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 Cu3d 9 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 H 2O(g) with α′ (H 2O(g)) = 1038.5 eV and β′ (H 2O(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.