FERROELASTIC DOMAIN-STRUCTURE IN THE VICINITY OF SUPERIONIC PHASE-TRANSITION IN CSDSO4 CRYSTALS

Ferroelastic reversible domain structure with ((2) over bar 03) and (1 01) domain walls is induced in CsDSO4 crystals by [100] and [001] comp ression at room temperature. About 3-4 K below the superionic phase tr ansition new (10 (1) over bar) domain walls appear in the crystal. Cha nges in the wedge-shaped domain pattern are observed also in (100) cut samples at temperature 3-4 K below T-s, both on heating and on coolin g (with thermal hysteresis of similar to 7 K). The changes of the doma in pattern in the close vicinity of T-s are related to an anomaly in t hermal expansion along the [001] direction reported at (T-s-3K) by Dil anyan and Shekhtman. Molecular model of the ((2) over bar 03) twin is proposed.