Some optical and thermal properties of CsCuCl3and its phase transition near 423K

Optical rotatory power, birefringence and thermal expansion were measured near the structural phase transition point of CsCuCl 3 . All these quantities show discontinuous changes at the transition point. Enantiomorphic domains were observed in the low-temperature phase and irreversible temperature dependence of the optical rotation angle is ascribed to this domain formation. Helical atomic displacements are explained in terms of the condensation of doubly degenerate E 1 phonon modes at +or-q0=(0 0+or-2 pi /3c) which is induced by the cooperative Jahn-Teller effect.