Determination of the crystal structure of the ɛ phase in the Fe–Al system by high-temperature neutron diffraction

The crystal structure of the high-temperature ɛ phase of the Fe–Al system has been determined by in-situ high-temperature neutron diffraction for the first time and the crystallographic parameters have been established by Rietveld refinement of the data. The ɛ phase was found to have a body-centered cubic structure of the Hume-Rothery Cu5Zn8-type (space group I  4¯3m (No. 217), Z = 4, Pearson symbol cI52, Strukturbericht designation D82). Accordingly, the ε phase has the formula Fe5Al8. Its lattice parameter is a = 8.9757(2) Å at 1120 °C, which is 3.02 times that of cubic FeAl (B2) at the same temperature. All fractional atomic coordinates, site occupation factors and interatomic distances were determined and it was examined how this phase can meet the rules for Hume-Rothery-type phases.