EXPERIMENTAL AND THEORETICAL-STUDY OF THE ELECTRONIC-STRUCTURE OF FE,CO, AND NI ALUMINIDES WITH THE B2 STRUCTURE

The differences in electronic structure of B2-type (CsCl) transition-m etal aluminides (FeAl, CoAl, and NiAl) have been investigated hy compa ring data obtained using electron energy-loss spectroscopy with theore tical calculations the spectra. The densities of states (DOS) for the three alloys calculated using the ab initio self-consistent linear muf fin-tin orbital method within the local density approximation have bee n compared. Using the unoccupied part of the DOS and the relevant tran sition matrix elements, energy-loss spectra have been calculated. It i s noted that ii rigid band model can only be considered as a first app roximation to calculate rile trends iii tile electronic structure of t he allays. The Al L(2-3) and K edges (providing information on s+d and p symmetry of final states at the Al sites, respectively) and the tra nsition-metal L(2-3) edges (s+d symmetry of final states al the transi tion-metal sites) have bren studied. Good agreement has been found bet ween experiment and calculations and, from the interpretation of spect ral details in terms of site and angular momentum decomposed density u f states, hybridization and interaction between the Al sp and TM d ban ds is observed and thus a covalent character in the bond is concluded. The differences in the electronic structure of the alloys studied, bo th iii terms of band filling and density of states at the Fermi level, have been correlated with the variation of the macroscopic properties of the materials.