The complex dielectric constant has been measured in a room-temperature ferroelectric liquidcrystal mixture. We have resolved the experimental data into the Goldstone mode and the soft mode and for each mode determined the dielectric strength and the corresponding relaxation frequency. The results are compared with the dielectric strength calculated using the extended Landau type of free-energy density proposed by Zeks [Mol. Cryst. Liq. Cryst. 114, 259 (1984)], and it is shown that this calculation is able to describe the experimental data well~We have shown that by reasonable assumptions we can derive a simple relation between the Goldstone-mode contribution to the dielectric susceptibility +2} and the polarization (Po), tilt (0O), and pitch (p) of the system: g2 --(Pop/00) /8%3~, where K3 is a bend nematic curvature elastic constant. We also predict, on theoretical grounds, a small peak of the dielectric strength to exist at T,.
The phase diagram of the deuteron glass Rbq (ND4), DsPO4 has been determined experimentally in the entire range of concentration z. A recently introduced temperature-frequency plot has been used to analyze the shape of the dielectric relaxation spectrum, indicating that in the glassy regime the longest relaxation time diverges according to the Vogel-Fulcher law. The corresponding Vogel-Fulcher temperature has been identified as the static limit of the freezing temperature Ty. The phase boundaries of the ferroelectric and antiferroelectric phases have been obtained in a standard manner by observing the peaks and breaks, respectively, in the temperature dependence of the quasistatic dielectric constant. It is shown that in a broad concentration range the observed phase diagram can be quantitatively described by a mean-field theory based on the static random-bond random-field model of dipolar glasses. The absence of macroscopic polarization in the ferroelectric region close to the glassy phase is probably due to the formation of microdomains in the presence of local random fields, however, recent NMR data suggest that a phase segregation between ferroelectric and glassy regions may occur.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.