Kaminsky: Reinvestigation of optical activity in the course of the ferroelastic phase transition in cadmium-langbeinite, K2Cd2(SO4)3. Phase Transitions (1996) in press.
The three tensor components of optical activity in orthorhombic K2Cd2(SO4)3 were determined at 298K, 417K and 443K . The room-temperature values of the rotatory power (omm-1) along , , and  are -2.7(9), -1.8(2), 2.9(5). The temperature dependence of optical activity along the optical axes was measured and is in accord for 300K and in the cubic phase with previous investigations. The thermal evolution of the optical activity reveals a steep step at the phase transition temperature of 432K. The calculation of optical activity and refractivity, employing a dipole-dipole model, is close to the experiment. The sign of the chirality of the samples is not affected by the transition. The value of the trace of the tensor components remains close to the cubic-phase value and is compatible with the symmetry breaking which is responsible for the observed anisotropy of the optical activity in the orthorhombic phase.