Domain structure and ferroelastic phase transition in (NH₄)₂SbF₅ single crystal

Abstract

Crystal of the (NH₄) SbF₅ has been grown and optical observations along the b-axis have been done in the temperature range 310 - 100 K. An appearance of stripe- and needle-like domains with domain walls parallel to (100) and (001) planes of the room temperature phase (above 292 K) was found at 292 K. No changes of domain structure was observed down to 100 K including the phase transition point at 169 K. The changes of domain pattern and monodomain state may be achieved by application of stresses to Y-45° cut samples. The results indicate that the phase transition at 292 K is a ferroelastic one.