No abstract

Electrically-induced behaviuor was compared in the non-stretched and uniaxially stretched poly(vinylidene fluoride-trifluoroethylenechlorofluoroethylene) terpolymer-a member of the relaxor polymer family that exhibits fast response speeds, a giant electrostriction, high electric energy density and a large electrocaloric effect. Although the temperature dependence of the low-field dielectric constant is almost identical, the dc bias electric field via a higher nonlinear contribution more heavily alters the dielectric response of the less-oriented non-stretched samples. Substantial differences in the polarization, electrocaloric response and induced electrostrictive strain of the non-stretched and stretched terpolymer suggest that electrically-induced properties of relaxor polymer films can be tailored by controlling the preparation conditions.

We have investigated dielectric properties of aromatic polythiourea (ArPTU, a polar polymer containing high dipolar moments with very low defect levels) thin films that were developed on Pt /SiO 2 substrate. The detected response is compared to the response of commercially available polymers, such as high density polyethylene (HDPE) and polypropylene (PP), which are at present used in foil capacitors. Stable values of the dielectric constant " 0 % 5 (being twice higher than in HDPE and PP) over broad temperature and frequency ranges and dielectric losses as low as in commercial systems suggest ArPTU as a promising candidate for future use in a variety of applications.

Dynamic processes in relaxorlike reduced poly͑vinylidene fluoride-trifluoroethylene͒ ͓P͑VDF-TrFE͔͒ copolymer have been studied by measurements of the temperature and frequency-dependent linear and thirdorder nonlinear dielectric response. Dielectric analysis of relaxor polymers has, namely, been incomplete until now, i.e., data interpretation was complicated by the fact that two similar types of dynamics, relaxorlike behavior in the crystalline part of the system and glass-to-rubber transition in the amorphous matrix, take place in the same temperature range and thus superimpose in the detected response. On the other hand, here, in the P͑VDF-TrFE͒ system, synthesized via reductive dechlorination from the poly͑vinylidene fluoride-chlorotrifluoroethylene͒, relaxor peaks take place at much higher temperatures, thus both dynamics can be investigated separately. Analysis of the experimental data reveals that the relaxorlike dielectric dynamics in the reduced P͑VDF-TrFE͒ copolymer, which is now not influenced by processes in the amorphous matrix, indeed is almost identical to that observed in classical relaxor systems and, furthermore, reminiscent of the dynamic behavior observed in various spin glasses. Also, a clear indication was obtained that all polar dynamic processes terminate down to Ϸ100 K and that below this temperature only nonpolar contributions govern the dielectric response of the reduced P͑VDF-TrFE͒ copolymer.

In CaCu 3 Ti 4 O 12 (CCTO), the ceramic material with the highest dielectric permittivity ever reported in a broad frequency and temperature range, the origin of such high permittivity has been attributed to 'electrical' heterogeneities in the microstructure. Dielectric investigations of CCTO ceramic thin films, performed in a broad temperature and frequency range, and the analysis in terms of the equivalent circle reveal that (i) each of the two constituents, insulating grain boundaries and semiconducting bulk grains, individually determines the dielectric behaviour of CCTO and (ii) manipulating the conditions under which CCTO ceramic thin films are prepared enables control of their dielectric properties.