Studies on structural phase transition and ferroelastic domain structures in K2SO4 crystal

The twinning in K2SO4 crystal grown from aqueous solution has been studied. Three orientational ferroelastic domains are found under a polarizing microscope at room temperature. As the sample crystal is heated up, the domain boundaries disappear and become single domain. The crystal undergoes a ferroelastic structural phase transition at 860K. The observed domain wall boundaries are analysed by using the property of elasticity of the crystal. The crystal is identified as the ferroelastic species 6/mmmFmmm. The permissible walls for any two adjacent domain pairs are derived by the symmetry approach to a crystal undergoing the structural phase transition. The twin structures taken across the domain boundaries are also presented.