Search

Dielectric properties of bitumen with different thicknesses were investigated by dielectric spectroscopy in the frequency range from 0.1 Hz to 1 MHz and temperature range from (−)40°C to 40°C. The ...

In this study, a hydrophobic silica aerogel was synthesized via one-step surface modification and polymer composite films based on a polyurethane (PU) matrix were prepared by doping with silica aerogel powder (at 2%, 3%, 5%, and 7% by weight = w/w%). The structural, thermal, morphological, and surface properties of the silica aerogel and PU composite films containing aerogel were investigated by Fourier transform infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry (DSC), scanning electron microscopy, and tensiometry. The dielectric properties of the silica aerogel and PU composite films containing the aerogel were determined over a temperature range of 293–423 K and a frequency range of 1–106 Hz. The contact angle of the silica aerogel was 106°. Moreover, the PU composite film with 7% aerogel had the highest contact angle (θ = 105°) among the composite samples, which was similar to contact angle of the silica aerogel. The dielectric constants and dielectric losses decreased with the frequency for all of the samples, whereas they increased with the temperature. The polarization regions and relaxation times were determined for all of the samples using the Cole–Cole equation. The glass-transition temperatures (Tg) were determined for the silica aerogel and PU composite films containing aerogel by dielectric spectroscopy and compared with the DSC results. The dielectric constants were lower for the PU composite films than the PU film. The dielectric constant for the PU composite film doped with 2% silica aerogel was 2.9 at 10 MHz. Thus, the PU composite with a low dielectric constant and dielectric loss factor (tanδ) could be regarded as a potential dielectric constant candidate, with possible applications as a dielectric material in the microelectronics industry.

Pure GaAs and GaAs1−xBix alloys with different Bi ratios (1 %, 2.5 %, 3.5 %) fitted with silver contacts were measured with a dielectric spectroscopy device. Dielectric characterization was performed at room temperature in the frequency range of 0.1 Hz to 1 MHz. GaAs exhibits three relaxation regions corresponding to space-charge, dipolar and ionic polarizations in sequence with increasing frequency while GaAs1−xBix samples show only a broad dipolar polarization in the same frequency range. This result proves the filling of the lattice with Bi through making a new bonding reducing the influence of ionic polarization. This finding supports the previous results concerning optical properties of GaAs1−xBix, presented in the literature.

Dielectric properties and AC conductivity of in-situ formed AuNPs/PEGMEA/PEGDA nanocomposite film was investigated at room temperature. Frequency dependent dielectric constant shows that there are two main relaxation mechanisms for both samples. First of these mechanisms which correspond to dipolar polarization of long polymer chain was observed at frequencies between 0.1 – 103 Hz, 0.1–104 Hz for PEGMEA/PEGDA film and AuNPs/PEGMEA/PEGDA nanocomposite film, respectively. This mechanism has dielectric constant of 10.8, 14.1 for PEGMEA/PEGDA film and AuNPs/PEGMEA/PEGDA nanocomposite film, respectively. The second mechanism which was attributed to dipolar polarization of chain branches was observed at frequencies between 102 – 106 Hz, 105–107 Hz for PEGMEA/PEGDA film and AuNPs/PEGMEA/PEGDA nanocomposite film, respectively. This mechanism has dielectric constant of 9.6 for PEGMEA/PEGDA film and 10.3 for AuNps/PEGMEA/PEGDA nanocomposite film which cured in the presence of Irg-907 as Type I initiator by using medium pressure mercury light. These relaxation mechanisms can also be detected at frequency dependence of dielectric dissipation (tan δ) as Cole-Cole fitted relaxation peaks and of AC conductivity graphs as frequency independent (DC-like), and frequency dependent regions. DC-like region, it was thought that the main effect of AuNPs was observed, has values for AuNPs/PEGMEA/PEGDA nanocomposite film and PEGMEA/PEGDA film as 6 × 10−7 and 2 × 10−8 S/cm, respectively. In addition to these two polarization mechanisms, electrode polarization was observed at frequencies lower than 1 Hz for AuNps/PEGMEA/PEGDA nanocomposite film due to accumulation of AuNPs.

In this report, the results of Dielectric and Raman spectroscopy of TlSe thin films are presented. The films were deposited in different thicknesses ranging from 290 angstrom to 3200 angstrom by thermal evaporation method. The relative permittivity (dielectric constant epsilon(r)') and dielectric loss (epsilon(r)'') of TlSe thin films were calculated by measuring capacitance (C) and dielectric loss factor (tan delta) in the frequencies ranging between 10(-2) Hz-10(7) Hz and in the temperature ranging between 173 K and 433 K. In the given intervals, both the dielectric constant and the dielectric loss of TlSe thin films decrease with increasing frequency, but increase with increasing temperature. This behavior can be explained as multicomponent polarization in the structure. The ac conductivity obeys the omega(s) law when s (s < 1). The dielectric constant of TlSe thin films is determined from Dielectric and Raman spectroscopy measurements. The results obtained by two different methods are in agreement with each other. (C) 2017 Elsevier B.V. All rights reserved.

Plasma polymerized poly(ethylene oxide) (pPEO) thin films were deposited by plasma assisted physical vapor deposition (PAPVD) with a constant thickness of 500 nm. The crosslinking density of pPEO films was controlled through the discharge power. Differential scanning calorimetry (DSC) and broadband dielectric spectroscopy (BDS) were applied to analyze the structural peculiarities of these coatings. Both DSC and BDS detected an increase of the crosslink density with power, which correlated with the increasing dynamic glass transition temperature (Tg). It was shown that plasma power changes the structure of plasma polymer, and dielectric spectroscopy may be a suitable technique for structural analysis.

A comprehensive analysis of the electrical conductivity of TlSbSe2 layered compounds prepared using the Bridgman–Stockbarger technique is presented. The temperature dependence of the electrical conductivity of TlSbSe2 and its anisotropy (as measured parallel and perpendicular to the layers) was studied for temperatures between 233 and 353 K. We show that the anisotropy of the electrical conductivity is temperature dependent. The ratio α of the conductivities parallel and perpendicular to the layers obeys an exponential law, with a barrier height of about 37 meV. The dielectric constant and dielectric loss of TlSbSe2 were determined using ohmic Au electrodes in the frequency range 10 Hz–100 kHz and within the temperature interval 233–373 K. The dielectric constant and the dielectric loss are found to decrease with increasing frequency and increase with increasing temperature. These behaviors are due to the polarization mechanisms in the samples. Lastly the activation energy values were derived from dielectric measurements.

In this study, it was aimed to prepare a series of PVdF-co-HFP based electrolytes with different LiClO4 loadings and to investigate their chemical and electrical properties in detail. For this purpose, PVdF-co-HFP based electrolytes with different LiClO4 loadings (1–20 weight %) were prepared using solution casting method. X-ray diffraction (XRD), differential scanning calorimetry, and thermogravimetric (TGA) –differential thermal and dielectric spectroscopy analysis of PVdF-co-HFP/LiClO4 were performed to characterize their structural, thermal, and dielectric properties, respectively. XRD results showed that the diffraction peaks of PVdF-co-HFP/LiClO4 electrolytes broadened and decreased with LiClO4. TGA patterns exhibited that PVdF-co-HFP/LiClO4 electrolytes with 20 wt % of LiClO4 had the lowest thermal stability and it degraded above 473 K, which is highly applicable for solid polymer electrolytes. Dielectric constant, dielectric loss, and conductivities were calculated by measuring capacitance and dielectric loss factor of PVdF-co-HFP/LiClO4 in the range from 10 mHz to 20 MHz frequencies at room temperature. In consequence, conductivities of PVdF-co-HFP/LiClO4 increased significantly with frequency for low loading of LiClO4 while they only slightly changed with higher LiClO4 addition. On the other hand, dielectric constant values of PVdF-co-HFP/LiClO4 films decreased with frequency whereas they rose with LiClO4 addition. The dielectric studies showed an increase in dielectric constant and dielectric loss with decreasing frequency. This result was attributed to high contribution of charge accumulation at the electrode–electrolyte interface. The electrolyte showed the maximum conductivity of 8 × 10−2 S/cm at room temperature.

We report on dielectric properties and ac conductivity of the TlSbTe 2 thin films grown by thermal evaporation on glass substrates at temperature range 293–373 K and measured over frequency range between 10 Hz and 100 kHz. The thicknesses of the films were between 200 A and 4000 A. It was found that dielectric constant ( e 1 ) of the TlSbTe 2 films changes between 39 and 740 and dielectric loss ( e 2 ) between 51-12,000 at 1 kHz and 293 K. The dielectric constant and dielectric loss were found to decrease with increasing frequency and to increase with increasing temperature. The dielectric constant exhibits bulk characteristics as the thickness exceeds 2000 A. The ac conductivity follows σ ( ω ) α ω s relation at frequencies higher than 1 kHz, and the dominant conduction mechanism is found to obey the Correlated Barrier Hopping (CBH) mechanism. At frequencies lower than 1 kHz, the electrical conduction is found to be in accordance with dc conduction mechanism. Analyzing the ac conductivity results, we show that as temperature increases, density of states near fermi level also increses from 10 19 to 10 21 cm −3 . Using frequency dependence of the dielectric constant, the maximum barrier height ( W m ), its temperature and thickness dependences are determined. The values for these parameters seem to agree with the theory of classical hopping of charge carriers over a potential barrier. XRD analysis reveal that crystal structure of bulk TlSbTe 2 is rhombohedral, whereas TlSbTe 2 thin film is found to be amorphous structure. Morever, the temperature coefficients of capacitance (TCC) and permittivity (TCP) were investigated for thin films of TlSbTe 2 .

Plasma poly(ethylene oxide) thin films at different thicknesses of 20, 100, 250, 500 nm were deposited by plasma-assisted physical vapor deposition on glass substrates between aluminum electrodes in capacitor form at 5 W plasma discharge power. The structural analyses were performed by Fourier transform in7frared spectroscopy. The dielectric properties such as dielectric constant κ′ and electric modulus M′′ were defined by dielectric spectroscopy measurements. Dielectric spectroscopy measurements were performed in the angular frequency range of 10−1–106 rad/s and temperature range of 353–173 K range. The measurement results showed that α, β, and γ-relaxations, which are the expected relaxations in polymeric structures, are effective on total polarization in the investigated frequency and temperature range. Dielectric constant exhibits an increase till 500 nm, then reaches a saturation behavior. When resonance angular frequencies belonging to α-relaxation were fitted by Vogel-Fulcher-Tamman equation. It was observed that glass transition temperatures increase with decreasing thickness. These results support the influence of the dead layer to total polarization and the dynamics of the structure. Besides, it was shown that dielectric spectroscopy is a useful way to analyze the glass transition temperature in thin film form.

A comparison of structure and dielectric properties of TlSbS2 thin films, deposited in different thicknesses (400–4100 A) by thermal evaporation of TlSbS2 crystals that were grown by the Stockbarger–Bridgman technique and the bulk material properties of TlSbS2 are presented. Dielectric constant e 1 and dielectric loss e 2 have been calculated by measuring capacitance and dielectric loss factor in the frequency range 20 Hz–10 KHz and in the temperature range 273–433 K. It is observed that at 1 kHz frequency and 293 K temperature the dielectric constant of TlSbS2 thin films is e 1=1.8–6 and the dielectric loss of TlSbS2 thin films is e 2=0.5–3 depending on film thickness. In the given intervals, both of dielectric constant and dielectric loss decrease with frequency, but increase with temperature. The maximum barrier height W m is calculated from the dielectric measurements. The values of W m for TlSbS2 films and bulk are obtained as 0.56 eV and 0.62 eV at room temperature, respectively. The obtained values agree with those proposed by the theory of hopping over the potential barrier. The temperature variation of ac conductivity can be reasonably interpreted in terms of the correlated barrier hopping model since it obeys the ω s law with a temperature dependent s (s

Cobalt Ferrite (CoFe2O4) nanoparticles coated with oleic acid were synthesized by polyol method. The structures of the nanoparticles were characterized by X-Ray Diffraction (XRD), Fourier Transform Infrared with Attenuated Total Reflectance Unit (FTIR -ATR). Thermal and morphological properties of nanoparticles were determined by thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and transmitting electron microscopy (TEM) respectively. The dielectric constant and dielectric loss of the nanoparticles were determined in the frequency range of 10 Hz–20 MHz and within the temperature range of 293 K–423 K. It was observed that AC conductivity σ(ω) α ωs. (0

The dielectric constant and the dielectric loss of tantalum pentoxide (Ta 2 O 5 ) thin films, produced by sol–gel spin-coated process on Corning glass substrates, have been investigated in the frequency range of 20–10 5 Hz and the temperature range of 183–403 K, using ohmic Al electrodes. The frequency and temperature dependence of relaxation time has also been determined. The capacitance and loss factor were found to decrease with increasing frequency and increase with increasing temperature. The activation energy values were evaluated and a good agreement between the activation energy values obtained from capacitance and dielectric loss factor measurements were observed.

The dielectric constant and the dielectric loss of TlSbSe 2 thin films, obtained via thermal evaporation of TlSbSe 2 crystals grown by Stockber-Bridgman technique, have been measured using ohmic Al electrodes in the frequency range 0.2–100 KHz and within the temperature interval 293–353 K. The capacitance are found to decrease with increasing frequency and increase with increasing temperature. The activation energy values were evaluated too. A good agreement between the activation energy values obtained from capacitance and dielectric loss factor measurements has been observed.

Sb2Te3 thin films of different thickness (23 – 350 nm) were prepared by thermal evaporation technique. The thickness dependence of the ac conductivity and dielectric properties of the Sb2Te3 films have been investigated in the frequency range 10 Hz- 100 kHz and within the temperature range 293-373K. Both the dielectric constant 1 and dielectric loss factor 2 were found to depend on frequency, temperature and film thickness. The frequency and temperature dependence of ac conductivity (σac(ω)) has also been determined. The ac conductivity of our samples satisfies the well known ac power law; i.e., σac(ω) ∝ ωs where s

Dielectric properties of Sb2Te3 films prepared by thermal evaporation technique onto clean glass substrates using ohmic aluminum electrodes have been investigated in the frequency range of 0.01– 100 kHz and within the temperature range of 293K– 373 K. Both the dielectric constant e1 and dielectric loss factor were found to depend on frequency and temperature. The activation values were evaluated and good agreement between the activation energy values obtained from capacitance and dielectric loss factor measurements were obtained.