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 chargetransfer calculations

Tha alloying behaviours of as-cast MoSi2 and MoSi2+xAl alloys have been stu died using high-energy XPS with Ct K-beta radiation. The charge transfer oc curring upon alloying was calculated using the variations in the Auger para meters of Mo, Si and Al between alloyed and unalloyed conditions and the li near potential model of Thomas and. Weightman and the non-linear potential model of Cole, Gregory and Weightman. In MoSi2 there was a significant incr ease in the Auger parameter of Si, while the shift in the Auger parameter o f Mo was negligible. The charge transfer towards the Si atoms was close to zero and is smaller compared to theoretical calculations. Tt is concluded t hat the atomic bonding between Mo and Si is of a covalent p d character. In MoSi2+xAl alloys, similar observations were made fur Mo and Si, while the Auger parameter of Al was reduced. Donation of electronic charge by Al atom s is possible: covalent bonds of Al with Mo are formed. The plasmon loss st ructures of the Si is and Al 1s peaks showed reduced intensity in the alloy s relative to the pure metals. This was attributed to more strongly bound v alence electrons. The opposite was the case for the Mo 2p(3/2) peak. The su bstitution of Si by Al atoms is confirmed, in agreement with previous studi es. (C) 2001 Acta Materialia Inc. Published by Elsevier Ltd. All rights res erved.