OPTICAL AND X-RAY STUDIES IN FERROELASTIC CS3H(SEO4)2

Optical observation of domain structures and X-ray examinations of Cs3 H(SeO4)2 were carried out above room temperature. The effect of an ext ernal force on the rearrangements of the constituent ions accompanied by the movement of domain boundary was studied at room temperature. Th e interrelations between unit cells in each phase were obtained above room temperature. When the crystal is warmed up through the phase tran sition at T(II), all the hydrogen bonds are instantaneously broken, an d then the hydrogen atoms are so rearranged as to form new hydrogen bo nds between two diffrent adjacent SeO4-2 tetrahedra. When the domain b oundary is moved, the SeO4-2 tetrahedra are tilted and displaced to ne w positions, and simultaneously hydrogen bonds are broken, and then ne w hydrogen bonds are reconstructed.