Effect of phase transition sequence on the ferroelastic domain structure of (NH4)(3)H(SeO4)(2) at room temperature

Temperature dependent evolution of ferroelastic domain structure in (NH4)(3)H(SeO4)(2) was studied. It was found that ferroelastic domain structure exists in phases III, IV, V and VI. Ferroelastic domain pattern at room temperature depends on which phase IV or II the crystal was transformed to room temperature, Transformation from paraelastic phase I gives very fine domains with different, domain wall orientations which are difficult to determine. Transformation from phase IV to phase III gives a completely different picture of ferroelastic domain, domains are coarse with well defined orientations of their boundaries.