Lattice Site Occupancy in Ternary Ordered Ni$\text{}_{3}$Al$\text{}_{1-x}$Fe$\text{}_{x}$ Alloys Estimated by EXAFS

Extended X-ray absorption fine structure (EXAFS) spectroscopy offers additional experimental evidence to the solution of site occupancy problem in ternary NiAlX alloys. A study of local order in the stoichiometric Ni$\text{}_{3}$Al$\text{}_{1-x}$Fe$\text{}_{x}$ ternary alloys (x = 0.02, 0.05, 0.10, 0.15, and 0.25) by EXAFS at the K-edge of Fe in the energy range from 7000 eV to 7600 eV are presented. Three models of substitutional behavior are considered - the preferential substitution of Fe atoms in: 1) Ni sites, 2) Al sites, 3) both sites. Data analysis was performed with theoretical and experimentally determined scattered photoelectron phases and amplitudes. The results of the EXAFS analysis are consistent with the picture in which most of the Fe atoms substitute Al sites and less than 25% of Fe atoms substitute Ni sites. Alloys with more than 10 at% of Fe showed higher tendency for ordering than those containing less than 10 at% Fe.