Experimental and theoretical investigations of EELS near-edge fine structure in TiAl with and without ternary addition of V, Cr, or Mn

Abstract

The intermetallic compounds TiAl without additives and with $\sim 5\mathrm{at}\%$ V, Cr, or Mn, have been studied by electron-energy-loss spectroscopy. Spectral shapes in the vicinity of the Ti $L_{2,3},$ Al $L_{2,3}$ and Al $K$ edges are investigated and compared with calculated spectra. Dipole selection rules $(\Delta l=\pm 1)$ apply, and $L$ edges thus provide information on $s+d$ final states, while $K$ edges provide information on $p$ final states. The theoretical densities of states have been calculated using the ab initio full potential linear augmented-plane-wave method, and, combined with the relevant matrix elements, theoretical spectra have been obtained. In calculating the electronic structure of ternary doped phases, a rigid-band model producing only variations in the Fermi level within the energy bands is used. This model shows good agreement with experiments. From the interpretation of the spectral features at the Al site (in doped as well as undoped phases) common, hybridized electronic states between the Al $\mathrm{sp}$ and Ti $d$ bands are observed. This is evidence of covalent bonding.