Determination of the structure of a new tetragonal U2FeAl20 phase

The atomic structure of a new ternary U2FeAl20 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 U2FeAl20 phase is tetragonal and belongs to the I4¯2m 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: Rp = 8.65%, Rwp = 11.2% and Rb = 5.93%.