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.

35000 g/mol moleküler ağırlığa sahip külçe halindeki polietilenden (PE), termal buharlaştırma yöntemiyle 10-3 Torr vakum altında 750 nm kalınlığında PE ince filmler elde edildi. PE ince filmler alüminyum (Al) elektrotlar arasında kapasitör formunda hazırlandı. Hazırlanan PE ince filmlerin 10-106 rad/s açısal frekans ve 233 – 373 K sıcaklık aralığında dielektrik ölçümleri yapıldı. Elde edilen sonuçlar Cole-Cole modeli ile analiz edildiğinde PE ince filmlerin dielektrik sabitinin oda sıcaklığında yaklaşık 20 olduğu, yapıda üç farklı polarlanma mekanizmasının farklı frekans ve sıcaklık aralıklarında etkili olduğu görüldü. Bu mekanizmalardan α-rölaksasyonunun polimerlerde gözlenen camsı geçiş davranışını temsil ettiği belirlendi. Vogel-Fulcher-Tamman (VFT) modeli kullanılarak yapılan analizde PE ince filmin camsı geçiş sıcaklığının 315 K (42ᵒC) civarında olduğu tespit edildi. PE ince filmin, termal buharlaştırma yöntemiyle üretilmesinde ana zincirinde kırılmalar meydana gelebileceği ve lineer bir zincir formundan çapraz bağlı ağ formuna geçilebileceği görülmüştür. Elde edilen sonuçlar PE’nin ince film formunda külçe formuna kıyasla daha yüksek dielektrik sabit değerlerine ulaşabildiğini göstermiştir. Buna göre, PE ince filmin mikro ve nano boyutta enerji depolama sistemlerinde kullanımı da mümkün olabilir.

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.

Thalium selenide (TlSe), which has a lattice with tetragonal symmetry, is a member of the A3B6 semiconductor group. The structure of TlSe is defined as chains where atoms inside are bonded with an ionic-covalent bond. TlSe thin films were deposited by thermal evaporation under a high vacuum on glass substrates. The structure of TlSe thin films is amorphous with a tetragonal structure. The AC conductivity measurements were operated via the measurements of capacitance and dielectric dissipation (tanδ) at room temperature. AC conductivity values change between 10−11 and 10−6 S/cm at the low-frequency side with decreasing thickness. Two different conduction regions were observed with increasing frequency. The region observed at the low-frequency side can be attributed to the motion of a chain-like part of the lattice, while the region observed at the high-frequency side can be attributed to side groups.

Plasma polymerized poly(ethylene oxide) thin film samples with thickness of 500 nm were deposited using plasma assisted physical vapour deposition at radio-frequency plasma discharge powers of 0, 2, 5 and 30 W, respectively. For comparison, a conventional poly(ethylene oxide) precursor was also investigated. In order to investigate the effect of the plasma discharge power on the cross-linking density of the plasma poly(ethylene oxide) and poly(ethylene oxide) precursors, structural characterization using differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy was performed. Structural analysis showed that the density of cross-linking increased upon increasing the plasma discharge power. This increase was observed as an increase in the dynamic glass transition temperature during the DSC measurements. In addition to these characterizations, the dielectric response of the thin film plasma poly(ethylene oxide) samples and poly(ethylene oxide) precursors were measured. The dielectric spectroscopy results showed that changes in the cross-linking density changed the alternative current (AC) conductivity. The measured glass transition temperatures obtained using DSC are in accordance with the glass transition temperatures obtained from the temperature-dependent AC conductivity results. It was observed that the temperature-dependent AC conductivity exhibits Arrhenius behaviour. The activation energies obtained for the plasma polymer samples showed an increase from 0.38 eV to 0.5 eV upon increasing the plasma discharge power. The plasma discharge power dependent activation energy results also indicate the fragmentation of long polymer chains into more smaller oligomers and radicals occurred upon increasing the plasma power.

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.

Polymers based on ionic conducting materials have important interest because of their potential applications in polymer electrolytes and membranes for fuel cell application. PVdF-co-HFP poly(viniliden-co-hexafluoropropylene) was chosen as a polymer matrix because of its high ionic conductivity and better mechanical properties. Polymer matrix composites were prepared with various amounts of LiClO4 salt by a solution casting method. The sample-ionic conductivity measurements were recorded by AC impedance analyzer at different frequencies from 0.1 Hz to 20 MHz and at different temperatures from 273 to 373 K. The changes of nanoscopic free volume and free volume fraction in these materials were investigated in terms of temperature from 273 to 373 K using Positron Annihilation Lifetime Spectroscopy (PALS) and Simha-Somcynsky (SS) Hole Theory. The free volume had a bump at about 3% in weight percentage of the salt and there is a slight increase after 10%. The effects of weight percentages of LiClO4 and temperature were investigated. The mechanism of the ac ionic conductivity was presented in terms of the free volume models, however thermo-occupancy function justifies the best accurate representation of the data.

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 .

In amorphous semiconductors and insulators, the using conductivity formulas are semi-empirical and have no satisfying physical explanations. A conductivity equation has been derived by Debye for the response of ideal materials which is rarely observed in practice, but a general conductivity equation which includes the previous empirical equations via a correct choice of arbitrary parameters and moreover totally theoretical derivation had to be generated. Hence, to determine the motion of electrons in the amorphous environment, we defined the equation of motion including viscous forces as a function of coordinates, their derivatives and time variables. We developed a fractional form of this equation over these three variables and finally obtained the most generalized equation of motion, which counts the overall interactions by a fractional form as a variation of two variable. The improved formula, called the stretched Havriliak–Negami equation, has the same form and behavior as the semi-empirical equation and reducible to the Cole–Cole and Cole–Davidson-type of conductivity.

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

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.