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 (Tc = 128°C) and tetragonal with the space group I41/amd above Tc . 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 Tc are broken instantaneously and the protons are hopping between the oxygen atoms.

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