The structural phase transition in anthracene—TCNB

Abstract

The problem of the orientational disorder in mixed stack charge transfer crystals has been addressed. X-ray diffraction data in the HT phase of A-TCNB are reported. They were analysed using conventional structure-refinement procedures and utilizing symmetry-adapted functions. For the HT phase, the orientational probability function allowed us to characterize as dynamic the disorder of the anthracene molecules. The soft mode was measured by Raman and coherent neutron scattering. Measurement by Brillouin scattering of the elastic constant C , , led to another determination of the soft mode. The behaviour of this soft mode allows one to conclude the existence of a mixed regime (between displacive and order-disorder) for the LT phase of A-TCNB.