DIELECTRIC STUDY OF PHASE TRANSITIONS IN 3-NITRO-4-CHLORO-ANILINE

3-nitro-4-chloro-aniline (NCA) exhibiting a phase transition between two solid phases has been studied by frequency domain dielectric spectroscopy. Dielectric studies show that molecular dynamics of NCA changes distinctly at the freezing point (370 K) and at the transition (242 K) from the high-temperature solid phase I(Ph I) to the low-temperature solid phase II(Ph II). In the Ph I just below the freezing point the molecules most probably perform a uniaxial fast reorientation around the pseudohexagonal symmetry axis of the benzene ring. On the other hand upon decreasing temperature in Ph I there are strong and temperature-dependent antiparallel correlations of molecular dipole moments. The correlations are of electrostatic origin and they cause a strong temperature dependence of the Kirkwood correlation factor leading to freezing out intermolecular reorientation. However, in the lower temperature range of the Ph I there is still an enhanced contribution to the static dielectric permittivity originating m...