Electronic structure and bonding in Mo_3Si, Mo_5Si_3, and Mo(Si,Al)_2 alloys investigated by x-ray photoelectron spectroscopy and density-functional theory

摘要

We have investigated the electronic structure of MoSi_2, Mo_5Si3, Mo_3Si, and Mo(Si_(1-x)Al_x)_2 alloys at a range of x values using a combination of valence-band x-ray photoelectron spectroscopy (VBXPS) and density-functional theory. We find good agreement between the experimental spectra and the calculated total densities of states. The observed differences between the VBXPS spectra for MoSi_2, Mo_5Si_3, and Mo_3Si are explained in terms of the various hybridizations, involving Si p and Mo d states, induced by the structural topology. The changes observed in the VBXPS spectra for Mo(Si_(1-x) Al_x)_2 alloys with increasing Al concentration are explained by a series of structural transformations and a downward shift of the Fermi energy due to the reduced electron concentration. Using rigid band arguments we discuss how this leads to a weakening of the covalent Mo—Si bonds and, hence, to increased ductility.