MICROWAVE DIELECTRIC-PROPERTIES OF DISUBSTITUTED DIACETYLENE DNP SINGLE-CRYSTALS

The dielectric properties of disubstituted diacetylene DNP single crystals were measured by microwaves in order to study the ferroelectric phase transition as a function of solid state polymerization. The high frequency properties of the permittivity were studied in DNP monomer and also in DNP crystals that were partially polymerized at a temperature of 130-degrees-C for different periods of time. At T(c) = 46.5 K the dielectric constant of the monomer shows a sharp peak. No change of this behaviour was found by cooling down for several times. The peak of epsilon' is getting flat and shifted to lower temperatures with advanced duration of thermal polymerization. The monomer crystals show a small peak of dielectric losses epsilon" infinity 1 at T(c). At the beginning of polymerization the peak height is getting larger and dielectric losses were measured down to 4 K. For polymerizing more than 3 h the maximum is reduced and flat; no losses at all are found after full polymerization.