Anomalous phase fluctuations accompanying the crystallographic phase transition in UNi2Sn

The phase transition in the Heusler compound UNi2Sn has been investigated by means of neutron powder diffraction and Sn-119 Mossbauer spectroscopy. It is shown that the low-temperature orthorhombic structure is gradually transformed into the high-temperature cubic structure between 200 and 330 K. Although the Mossbauer spectra for these two phases are virtually identical, an extraordinary line broadening is observed in the transition region. The broadening is explained in terms of the thermal excitation of domain walls, moving on the Mossbauer time scale. The atoms must hop continuously between cubic and orthorhombic positions.