DOMAIN-STRUCTURE AND THERMAL-BEHAVIOR OF CSDSO4 CRYSTAL

Polarization microscope studies of single domain (001) cut CsDSO4 samp les reveal numerous (100) ferroelastic domain walls at similar to 416 K. The domain pattern disappears above T-s = 421 K. On cooling the (10 0) twin structure occurs in temperature range 417-413 K. A model of cr ystalline structure of (100) domain walls in the (001) surface is prop osed and related to the displacement of both Cs and SO4 along [100] di rection. Total entropy change in the superionic phase transition regio n obtained from DSC measurement amounts to 1.68 R and exceeds the conf igurational entropy value 1.39 It related to the change in the equival ent position of DSO4 groups at T-s.