D.-Y Kim, W. Kaminsky and A.M. Glazer: A low-temperature tilter system and its application to the measurement of the anisotropy of optical rotation in K2ZnCl4 in the vicinity of the phase transition at 145K.

The ferroelectric/ferroelastic phase transition of K2ZnCl4 at 145K has been investigated employing the tilter method (Kaminsky, W. and A. M. Glazer (1996) Ferroelectrics 183, 133) which was adapted to low-temperature experiments. We were able to observe the anisotropy of optical rotation in K2ZnCl4 which shows a distinct discontinuity at the transition temperature. A precursor - optical rotation in the ferroelectric phase is discussed in connection with a cluster ordering scheme suggested in an earlier x-ray study. The rotation of the optical indicatrix which accompanies the transition from the orthorhombic to the monoclinic system shows a Landau - type temperature dependence. Model calculations based on the dipole-dipole interaction between the atoms of the structures at different temperatures are in qualitative agreement with the experimental results.