On the Phase Transition of Chloranil (2,3,5,6-Tetrachloro-p-Benzoquinone)

Abstract

Experiments of Zeeman effect of ³⁵Cl nuclear quadrupole resonance on single crystals of chloranil below and above the second order phase transition point (95 K) determined the electric field gradient tensors and suggested a coupling of an acoustic shear strain wave to the soft librational mode associated with the phase change. The previously proposed dynamical model of the transition was reexamined and its mechanism was discussed on the basis of the symmetry consideration with respect to the soft librational and the shear strain modes. Different behaviors of crystals with different growth habits are reported.