An X-ray spectroscopic study of Co-Al alloys

Abstract

The X-ray K absorption spectrum of cobalt is studied for the pure metal and also for three of its alloys in the Co-Al phase with 45, 50 and 60 atomic per cent of cobalt. Each spectrum shows a main edge (K discontinuity) and associated fine structure, extending up to 250 eV for the pure metal and 180 eV for the alloys. The main edges in the alloys are interpreted on the basis of Carter's model (1971), which is concerned with the overlap of electron orbitals and with the defect structure of the phase. Application of the Lytle theory (1966) in order to explain the fine structure shows that the Lytle plots for the 50 at.% alloy and the pure metal pass through the origin while those for the 45 and 60 at.%Co alloys do not. This may be because the 50 at.% alloy and the pure metal are perfectly ordered structures, CsCl-type and HCP respectively, whereas the 45 and 60 at.%Co alloys have defect structure, with Al vacancies and substitutional Co respectively.