Optical studies of the ferroelastic phase transitions in Rb₃H(SeO₄)₂, (NH₄)₃H(SO₄)₂ and (NH₄)₃H(SeO₄)₂

Abstract

Abstract Optical observations of growth twins and ferroelastic domains and measurements of the rotation of the optical indicatrix were carried out for Rb3H(SeO4)2 and (NH4)3H(SO4)2 using an optical microscope. Taking into account the symmetry reduction from the rhombohedral (Rm) to the monoclinic phase (B2/a) the occurrence of domains and growth twins can be well described. The orientations of oblique ferroelastic walls are well determined by the spontaneous strains s e 11 and s e 23 at room temperature.