Investigation of the ε phase in the Fe–Al system by high-temperature neutron diffraction

In the central part of the Fe–Al system between about 58 and 65 at.% Al, a high-temperature phase denoted as e occurs with a hitherto unknown crystallographic structure. The phase is stable between 1231°C and 1095°C. In order to study the crystallographic structure of the e phase, in situ high-temperature neutron time-of-flight diffraction experiments have been performed at the HIPPO instrument at the Los Alamos Neutron Science Center (LANSCE). The e phase was found to have the formula Fe5Al8 with a body-centred cubic structure of the Hume–Rothery Cu5Zn8 type (I\(\bar{4}3\)m (No. 217), Z=4, cI52) and 52 atoms in the unit cell. Its lattice parameter is a=8.9756(2) A at 1120°C, which is 3.02 times that of cubic FeAl (B2) at the same temperature. We report here the evolution of the crystallographic parameters over the temperature range between 1080°C and 1120°C.