EELS near-edge structure in the Laves-phase compounds TiCr2 and TiCo2:: Theoretical and experimental studies -: art. no. 214107

Laves-phase compounds TiCr2 and TiCo2 have been investigated by electron energy loss spectroscopy (EELS), and ab initio calculations have also been performed to relate the experimental spectra based on the method of augmented plane waves plus local orbitals (APW+lo) with the generalized gradient approximation. It is shown that the normalized EELS cross sections of Ti L-2,L-3 edges change only slightly between TiCr2 and TiCo2 compounds, and that variations of the calculated valence charge redistributions between these compounds are negligible. Therefore, there are no significant charge transfers between Ti and Cr (Co) atoms, and the local charge neutrality approximation is valid in these compounds. The charge densities of these compounds were also theoretically investigated. The results reveal a relatively strong covalent nature of atomic bonds between Cr-Cr (Co-Co) atoms compared with that between Ti and Cr (Co) atoms in TiCr2 and TiCo2, respectively. It is also demonstrated that the covalent bonding of the atoms in TiCo2 is stronger than that in TiCr2. This result could explain the significant difference of the calculated enthalpies of formation between TiCr2 and TiCo2 compounds.