X-ray absorption spectroscopy, EELS, and full-potential augmented plane wave study of the electronic structure ofTi2AlC,

The structural parameters of various H\"agg phases ($H$ or ${M}_{n+1}A{X}_{n}$ phases) are studied experimentally by x-ray and electron spectroscopies, x-ray diffraction, and ab initio full potential as well as full mutiple scattering theoretical calculations. Experimentally it was found that the structure of all ternary compounds analyzed herein are relaxed. The values of the lattice parameters and relaxations obtained from ab initio calculations are in excellent agreement with those deduced from the analysis of the experimental data. The bonding scheme has been analyzed and the charge transfer between constituting atoms determined. It is demonstrated that the strength and electrical transport properties in these materials are principally governed by the metallic planes. For the solid solution ${({\mathrm{Ti}}_{0.5}{\mathrm{Nb}}_{0.5})}_{2}\mathrm{Al}\mathrm{C}$, the most salient result is that the basal planes are corrugated, which could explain the solid solution scattering observed in this $H$ phase.