Bonding mechanisms in gamma-TiAl: comparison between absorption near edge fine structures and theoretical predictions

The near edge fine structures of the gamma-TiAl alloy recorded either in XA S (K edges) or in EELS (L edges) have been compared with calculations based on band structure or full multiple scattering techniques. Good agreement b etween experiment and theory has been achieved for the Ti-K, Al-K and AI-L edges. The discrepancy observed between experiment and theory at the Ti-L-2 3 edges is interpreted as the failure of the single particle approximation at these edges due to core hole and strong exchange interaction. Strong hyb ridization between the Ti and AI atoms is demonstrated and supported by ana lysing charge density maps obtained from the band structure calculations. T he existence of Ti-d-Al-p, Ti-d-Al-s and Ti-d-Ti-d hybrids, and therefore c ovalent character in the bonding, are discussed in terms of the mechanical properties of the gamma-TiAl alloy.