An experimental study of bonding and crystal structure modifications in MoSi2 and MoSi2+xAl (x=10 to 40 at% Al) via Auger parameter shifts and charge transfer calculations Original Research Article

The alloying behaviours of as-cast MoSi2 and MoSi2+xAl alloys have been studied using high-energy XPS with Cr Kβ radiation. The charge transfer occurring upon alloying was calculated using the variations in the Auger parameters of Mo, Si and Al between alloyed and unalloyed conditions and the linear potential model of Thomas and Weightman and the non-linear potential model of Cole, Gregory and Weightman. In MoSi2 there was a significant increase in the Auger parameter of Si, while the shift in the Auger parameter of Mo was negligible. The charge transfer towards the Si atoms was close to zero and is smaller compared to theoretical calculations. It is concluded that the atomic bonding between Mo and Si is of a covalent p–d character. In MoSi2+xAl alloys, similar observations were made for Mo and Si, while the Auger parameter of Al was reduced. Donation of electronic charge by Al atoms is possible; covalent bonds of Al with Mo are formed. The plasmon loss structures of the Si 1s and Al 1s peaks showed reduced intensity in the alloys relative to the pure metals. This was attributed to more strongly bound valence electrons. The opposite was the case for the Mo 2p3/2 peak. The substitution of Si by Al atoms is confirmed, in agreement with previous studies.