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We demonstrate that commercially available window tinting films could be used multifunctionally, i.e., for electromagnetic shielding and absorption at frequencies below 1 THz along with visible light and ultraviolet protection. The fine control of the film optical properties by their structural composition can also be used to extend their performance to the lower frequency ranges, i.e., terahertz and microwave. The electromagnetic properties of two types of thin protective films loaded with either carbon or iron oxide micro- and nano-inclusions were studied in microwave (12–18 GHz) and terahertz (0.2–1.0 THz) frequency ranges vs their inner structure. The reflection and transmission coefficients of studied tint films were investigated using waveguide and free space measurements and compared with theoretical modeling results. The effective sheet resistance was estimated from the experimental data. [ABSTRACT FROM AUTHOR]

Results of broadband dielectric investigations of 0.94PbMg1/3Ta2/3O3-0.06PbTiO3 (0.94PMT-0.06PT or PMT-PT) crystals in wide temperature range from 100 K to 950 K are presented. Below 300 K the dielectric properties of crystals are governed by polar nanoregions dynamics. However, at higher temperatures (above 600 K) the electrical conductivity effects also become important. The electrical conductivity occurs presumably due the hopping of oxygen vacancies and demonstrates change in the activation energy close to 750 K. The change in the activation energy can be explained by increase of concentration of single ionized vacancies. No anomaly in the temperature dependence of the static dielectric permittivity was observed in wide temperature range from 213 K to 950 K and the dependence was successfully described by spherical random bonds random fields theory. Moreover, two different contributions were successfully separated in the distributions of relaxation times in PMT-PT crystals. These contributions were attributed to different polar nanoregions dynamics. Moreover, the different freezing temperatures values were obtained for most probable and longest relaxation times, which was explained with an idea of continuous distribution of relaxation times broadening on cooling in relaxors. The critical remarks about the Vogel-Fulcher law application for relaxors are addressed in the paper. [ABSTRACT FROM AUTHOR]

Dielectric/electric properties of onion-like carbon (OLC)/polydimethylsiloxane composites were investigated over very wide frequency (20 Hz-3 THz) and temperature (26-500K) ranges. The percolation threshold in these composites strongly dependents on the OLC aggregate sizes and was lowest for the composites with the smallest OLC aggregate sizes (~40 nm). Interestingly, the transition into the insulator state of the composites occurred at higher temperatures. The transition temperature increases with OLC aggregate concentration. Above the percolation threshold, the electrical conductivity in the composites occurs mainly due to electron tunneling between OLC clusters and quasi-one-dimensional hopping inside the clusters. The hopping almost vanishes at frequencies above 100GHz where the phonon contribution dominates. [ABSTRACT FROM AUTHOR]

The dielectric behavior of the Ba(Ti0.8Ce0.2)O3 ceramics was studied by broadband dielectric spectroscopy in a temperature interval 140–500 K. The broad dielectric relaxation was analyzed by the Havriliak–Negami relationship and the distribution of relaxation times formalism. It was found that the Havriliak–Negami average relaxation time, longest and most probable relaxation times from the distribution of relaxation times follow the Vogel–Fulcher law. The freezing temperature of the longest relaxation time is substantially higher than the freezing temperature of the most probable relaxation time, indicating the distribution of freezing temperatures. The dielectric dispersion has all features inherent to relaxor ferroelectrics and the relaxation is assigned to the dynamics of polar nanoregions. [ABSTRACT FROM AUTHOR]

Electrical transport properties of onion-like carbon (OLC) based composites over a wide (20 Hz-4 THz) frequency range are reported. The dependencies of dc conductivity on temperature can be approximated by the Mott law for one-dimensional variable range hopping below 130 K and by the typical law for fluctuation induced tunneling within the range of 130-300 K. The critical frequency at low temperatures also decreases according to the Mott law for one-dimensional variable range hopping. It was demonstrated that OLC annealing temperature plays a high role on the dielectric and electrical properties of composites at low temperatures. In the terahertz frequency range, the main contribution to the complex electrical conductivity is due to the phonon contribution while the contribution from hopping conduction vanishes at these frequencies. [ABSTRACT FROM AUTHOR]

The dielectric response of Rb0.5(ND4)0.5D2PO4 (DRADP-50) dipolar glass has been studied at low temperatures. From the experimental results, the distribution of the relaxation times and of the local polarization at various temperatures is calculated. It is shown that the local-polarization distribution function obtained from the dielectric response &eh;*(ν,T) is consistent with that obtained from NMR results. The results also show that the dielectric dispersion is due to diffusion, creation, and annihilation of Takagi groups. [ABSTRACT FROM AUTHOR]

Relaxor ferroelectric PbMg1/3Ta2/3O3 ceramics and thin films were investigated by means of broad-band dielectric, time-domain terahertz (THz), and Fourier-transform infrared (IR) spectroscopy in the frequency range 100 Hz–90 THz at temperatures 100–490 K; the THz and IR spectra were studied from 20 to 900 K. A diffused and strongly temperature dependent peak in the complex permittivity is caused by a dielectric relaxation due to the dynamics of polar clusters. The relaxation appears below the Burns temperature Td in the THz range; it slows down on cooling through the microwave and MHz range and anomalously broadens. The shortest and longest relaxation times of the distribution of relaxation times follow Arrhenius and Vogel–Fulcher laws, respectively. The degree of the B-site order has only a small influence on the parameters of the dielectric relaxation and almost no influence on the phonon parameters. Below Tm≅180 K the distribution of relaxation frequencies becomes broader than our experimental spectral range, and frequency independent dielectric losses develop below 100 GHz in the spectra. Although the macroscopic crystal structure is cubic, IR spectra give evidence about the lower local symmetry, which can be assigned to the presence of the polar clusters below Td. Infrared spectra above Td still reveal more modes than predicted by selection rules in the paraelectric phase of the Fm3m space group so that we suggest selection rules which take into account chemical inhomogeneity in the β″-perovskite sublattice. [ABSTRACT FROM AUTHOR]

Results of broadband dielectric/electric investigations of Bi(Mn0.33Nb0.67)O3.1 ceramics are presented in wide frequency range 20 Hz–3 GHz. The electric properties of Bi(Mn0.33Nb0.67)O3.1 ceramics are mainly governed by high conductivity. The relaxation process, related to electrical conductivity, was detected. No polar phase transition was detected in Bi(Mn0.33Nb0.67)O3.1 ceramics by broadband spectroscopy. Bi(Mn0.33Nb0.67)O3.1 ceramics also not exhibit ferroelectric relaxor behavior. [ABSTRACT FROM AUTHOR]

Broadband dielectric properties of tungsten disulfide (WS2) nanotubes/polyurethane (PU) composites over a wide temperature range (300 K–450 K) are presented for concentrations up to 2 wt%. Although no electrical percolation was observed in composites, at room temperature the dielectric permittivity of thermosetting composites with 2 wt% inclusions is 2 times higher than the dielectric permittivity of the pure polymer, that indicate that the composites are suitable for antistatic applications. Broadband dielectric properties of the composites are mainly governed by the α relaxation, the dynamics of the "soft" molecular segment of the PU chain. The Vogel temperature decreases with increase in the concentration of the WS2 nanotubes. At higher temperatures (above 380 K) the electrical conductivity dominates in properties of pure PU and composites with the WS2 inclusions as well. The DC conductivity increases with the WS2 concentration in thermosetting composites, while its activation energy is almost independent from the WS2 concentration far from melting point. The DC conductivity has some change in slope close to 420 K. Above room temperature, the large ultrasonic relaxational attenuation maxima and the velocity dispersion were observed. It was found that the attenuation peak in composites shifted to lower temperatures after addition of nanoparticles. The ultrasonic attenuation data of thermosetting composites were fitted to the relaxation equation with the single temperature‐dependent relaxation time. The thermal activation energy of the relaxation process, which was calculated from the ultrasonic data, was found to increase in PU with the concentration of WS2 nanotubes. POLYM. COMPOS., 39:4477–4485, 2018. © 2017 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]