Unusual complex high temperature structure of Fe2VSi

The α-Mn structure (A12) has been found above 1373 K as a new structure of Fe2VSi, which has the Heusler structure (L21) at room temperature. The Fe2VSi alloy with a single phase of the α-Mn structure was produced using the melt-quenching technique. When the sample was annealed at 1073 K, it transformed into the Heusler structure. In the next step, the Heusler Fe2VSi was annealed again at 1373 K and quenched into ice water, then the sample almost returned to the α-Mn structure. Detail of the crystal structure was investigated on the α-Mn phase by the neutron diffraction measurement. The high temperature α-Mn phase has more complex structure than the low temperature Heusler phase, and it is very unusual transformation because usually a high temperature phase has a simpler structure than its low temperature phase.