X-ray diffraction study of the ferroelastic phase transition in CsHSeo₄

Abstract

The crystal structure of CsHSeO₄ at room temperature was determined by making use of an automatic four-circle X-ray diffractometer. The crystal is monoclinic with the space group P2₁/c below the ferroelastic phase transition temperature (T_c = 128°C) and tetragonal with the space group I4₁/amd above T_c . CsHSeO₄ exhibits feature of one-dimensional arrangement of hydrogen bond chains along the c axis in the room temperature phase.

By the consideration of possible rearrangements of the constituent ions accompanied with the movement of the domain boundaries, it is strongly suggested that hydrogen bonds in CsHSeO₄ above T_c are broken instantaneously and the protons are hopping between the oxygen atoms.