Optical and X-Ray Studies in Ferroelastic Cs₃H(SeO₄)₂

Abstract

Optical observation of domain structures and X-ray examinations of Cs 3 H(SeO 4 ) 2 were carried out above room temperature. The effect of an external force on the rearrangements of the constituent ions accompanied by the movement of domain boundary was studied at room temperature. The interrelations between unit cells in each phase were obtained above room temperature. When the crystal is warmed up through the phase transition at T II , all the hydrogen bonds are instantaneously broken, and then the hydrogen atoms are so rearranged as to form new hydrogen bonds between two diffrent adjacent SeO 4 -2 tetrahedra. When the domain boundary is moved, the SeO 4 -2 tetrahedra are tilted and displaced to new positions, and simultaneously hydrogen bonds are broken, and then new hydrogen bonds are reconstructed.