Studies on the Local Structure of Dilute 3d Transition Metal Ternary Dopants in L1₂ Ordered Ni₃Al-Based Alloys

Abstract
We have utilized the technique of XAFS to study the local environment of transition metal (TM) ternary dopants (Ti, V, Cr, Mn, Fe and Co) in Ni₇₅TM_xAl_25-x. In γ-Ni₃Al, the first shell around Al consists of 12 Ni atoms. Ni is surrounded by 8 Ni and 4 Al atoms. In all cases, the dopant K-edge XAFS results show only Ni backscattering contribution in the first peak of the Fourier transform. Al backscattering contribution is either completely absent or is so weak that it is masked by the strong dopant-Ni bond. The number of Ni near neighbors suggests that for Ti, V, Cr, Mn and Fe absorbers, a majority of the dopant atoms occupy the Al sublattice. However, even in the case of Co dopants where studies by others indicate that the Co atoms occupy the Ni sublattice, no Al backscattering contribution can be detected. Also, the XANES of the various dopants exhibit a special feature at the edge, which appears to be due to p-d mixing.