Dielectric characterization of the B[sub 7] and a B[sub X] phase.

The first clear experimental evidence of a dielectric relaxation in the B[sub 7] 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-B[sub 7] pointing to a co-operative motion of ferroelectric clusters. Furthermore, a phase transition B[sub 7]-B[sub X] is observed. The values of about 10 for the high frequency limit of the dielectric constants of the B[sub 7] and B[sub X] 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[sup -8]s, i.e. the experimental limit. Only in the supercooled B[sub X] 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. [ABSTRACT FROM AUTHOR]