Dielectric characterization of samples showing the SmCPA/B7 transition

Dielectric measurements on samples consisting of banana-shaped molecules with a polymorphism I/SmCP_A/B₇ have been performed for the first time. The dielectric increment for the reorientation of the molecules about the long axis, and the corresponding relaxation time, surprisingly decrease at the SmCP_A/B₇ transition. This effect is discussed in terms of the undulated structure which partially destroys the ferroelectric short range order. Decreasing temperature gives an even stronger hindrance for this reorientation and could explain controversial results obtained in the B₇ phases of different samples. At lower temperatures a further mesophase was detected. This was additionally observed by calorimetric and atomic force microscopy methods.