- The atomic structure of a new ternary U 2 FeAl 20 phase appearing in the Al-rich corner of a U–Fe–Al system was solved using electron crystallography and X-ray powder diffraction techniques (XRD). The positions of U atoms were determined from crystallographically processed high-resolution electron microscopy (HRTEM) images. These positions were used as a starting set for determining the coordinates of Fe and Al atoms by difference- Fourier synthesis technique. The U 2 FeAl 20 phase is tetragonal and belongs to the I 4¯ 2 m space group. Its unit cell contains 80 Al, 4 Fe, and 8 U atoms. The lattice parameters obtained after Rietveld refinement are: a= 12.4138 Å, c= 10.3014 Å. The reliability factors characterizing the Rietveld refinement procedure are: R p= 8.65%, R wp= 11.2% and R b= 5.93%.