Dielectric characterization of the B7 and a BX phase

Abstract

The first clear experimental evidence of a dielectric relaxation in the B7 phase is given. The associated molecular process is probably the reorientation of the bent-shaped molecules about the long molecular axis. It is also shown that the dielectric constant strongly increases at the phase transition I-B7 pointing to a co-operative motion of ferroelectric clusters. Furthermore, a phase transition B7-BX is observed. The values of about 10 for the high frequency limit of the dielectric constants of the B7 and BX phases and the static dielectric constants of the isotropic phase are in agreement. Thus, in all the phases the main dipoles can reorient faster than 10−8 s, i.e. the experimental limit. Only in the supercooled BX phase were the dynamics of the transversal dipoles measured. Using atomic force microscopy, focal-conic domains modulated by parallel lines have been observed at room temperature.