Dielectric characterization of the B₇ and a B_X 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-B_X is observed. The values of about 10 for the high frequency limit of the dielectric constants of the B₇ and B_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 10⁻⁸ s, i.e. the experimental limit. Only in the supercooled B_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.