An application of Ti-K X-ray absorption edges and fine structures to the study of substoichiometric titanium carbide TiC1-x

Abstract

High-resolution measurements of the X-ray absorption coefficient were made around and up to 1000 eV above the titanium K-edge of TiC 1−x samples (0.5≤1−x≤0.97). When increasing the carbon vacancy content x, (i) the positive effective charge of titanium deduced from the edge-shift decreases, (ii) the bottom of the titanium 4p bands (situated at 10-15 eV above the Fermi level E F in TiC 0.97 ) moves down progressively towards E F . From the increased damping of the Exafs oscillations with non-stoichiometry, average mean-square static relative displacements of titanium-titanium and titanium-carbon first neighbours are evaluated. A simple model where each carbon vacancy repells its first neighbours Ti by 0.08 A is proposed Mesures a haute resolution des coefficients d'absorption de rayons X au voisinage du seuil K de Ti et jusqu'a 1000 eV au-dela pour 0,5≤1−x≤0,97: quand la teneur x en lacunes de C augmente, la charge effective positive de Ti deduite de l'energie de seuil, diminue et le bas des bandes 4p de Ti se deplace vers E F . A partir de l'amortissement des oscillations EXAFS, evaluation des deplacements relatifs statiques quadratiques moyens des premiers voisins Ti-Ti et Ti-C. Proposition d'un modele ou toute lacune de C repousse ses premiers voisins de 0,08 A