Electronic structure and bonding in Mo3Si, Mo5Si3, and Mo(Si,Al)2 alloys investigated by x-ray photoelectron spectroscopy and density-functional theory
We have investigated the electronic structure of MoSi2, Mo5Si3, Mo3Si, and Mo(Si1−xAlx)2 alloys at a range of x values using a combination of valence-band x-ray photoelectron spectroscopy sVBXPSd and densityfunctional theory. We find good agreement between the experimental spectra and the calculated total densities of states. The observed differences between the VBXPS spectra for MoSi2, Mo5Si3, and Mo3Si 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(Si1−xAlx)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.