Neutron diffraction study of the structural phase transition in SnS and SnSe

Abstract The structural phase transitions in SnS and SnSe have been investigated by neutron diffraction in the temperature range 295–1000 K using a high temperature furnace. Accurate positional and thermal parameters have been obtained as a function of temperature both in the α- (GeS-type, B16) and β-phase (TlI-type, B33). These investigations indicate that the α → β phase transitions in SnS and SnSe are of second order displacive type, and consist mainly of the continuous movement of Sn and S/Se atoms almost entirely along the [100] direction, and suggest the soft-mode behaviour of a zone-boundary phonon of the β-phase.