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Tungsten Disulfide Polythiophene Nanocomposites
Published in Mahmood Aliofkhazraei, Advances in Nanostructured Composites, 2019
Nicole Arsenault, Rabin Bissessur, Douglas C. Dahn
The first examples of nanocomposites composed of graphene analogous WS2 and conductive polythiophene were synthesized and characterized by FTIR, TXRF, SEM, and PXRD. The electronic conductivity of these nanocomposites was measured by the co-linear four-probe technique and by the van der Pauw technique in air and under vacuum and at variable temperatures. The nanocomposites synthesized showed structural characteristics similar to PT, and all the black nanocomposites showed significantly higher conductivity values than the pure PT. The conductivity of the 5% nanocomposite was over one order of magnitude higher than pure PT, with the highest average conductivity at (3.7 ± 0.7) × 10−1 S/cm. The variable-temperature conductivity showed variable-range hopping (Mott Law) behavior for most samples, with the conductivity decreasing with decreasing temperatures. The results shown here demonstrate the possibility for exfoliated graphene-analogous compounds to enhance the conductivity of conductive polymers. Similar conductivity enhancement has also been seen in polyaniline/WS2 nanocomposites (Lane et al. 2016). Future studies on these types of nanocomposites are needed to determine how exfoliated graphene-analogous compounds play a role in the enhanced conductivity of the nanocomposites in order to better understand and design new conductive materials.
Thermoelectric Properties of High-Temperature Superconductors
Published in D.M. Rowe, CRC Handbook of Thermoelectrics, 2018
In the case of an energy-independent density of states, we are in the Mott's variable range hopping regime, with a = '/j for two dimensions and a = 'A for three dimensions. Shldovskii and Efros20 have analyzed the case of low carrier concentrations, where electrons interact via the unscreened Coulomb potential, and they obtained a = '/: for any dimensionality.
Different Analytical Models for Organic Thin-Film Transistors: Overview and Outlook
Published in Brajesh Kumar Kaushik, Nanoscale Devices, 2018
In the disordered amorphous structure of organic materials, the charge transport occurs by variable range hopping (VRH) of charge carriers between strongly localized states [8–29]. The VRH model was proposed by Vissenberg and Matters in order to model the electrical characteristics of OTFTs [8]. It considers the hopping percolation of charge carriers between the localized states. In order to obtain an analytical expression of the drain current based on the VRH model, it is assumed that the current transport is parallel to the insulator–semiconductor interface [18].
Dielectric properties of calcium-substituted lanthanum ferrite
Published in Journal of Asian Ceramic Societies, 2020
Refka Andoulsi-Fezei, Nasr Sdiri, Karima Horchani-Naifer, Mokhtar Férid
Apart from lanthanum substitution, the introduction of isovalent or heterovalent cations to the iron site seems to be interesting. In fact, we have already studied the influence of zinc incorporation in a previous work. Promising results were obtained and a significant conductivity improvement with the substitution reported [13]. Titanium-substituted ferrites, on the other hand, exhibit an enormous dielectric constant of between 5.103 and 11.103 at 100 Hz [14]. Likewise, Idrees et al. [15] investigated the conduction and relaxation phenomena of LaFe0.9Ni0.1O3 between 1 Hz and 10 MHz. They proved that at below 296 k, variable-range hopping is adequate to describe the conductivity. However, small polaron hopping becomes a suitable parameter at above that temperature.
Dielectric, impedance and modulus spectroscopy of Ta-based layered perovskite
Published in Phase Transitions, 2019
P. L. Deepti, S. K. Patri, R. N. P. Choudhary, P.S. Das
Further, two types of hopping charge mechanisms were introduced for understanding of the conduction mechanism; the nearest neighbor hopping (NNH) and variable range hopping (VRH). NNH successfully takes place in between the concerned ion and the nearest vacant sites. As the ion hopped to the nearest vacant site, the nearest ion eases to its position successfully. This yields a long-range movement in the non-dispersive region and producing dc conductivity. The VRH occurs when the concerned ion is incapable of easing to its position, pushed back to its preliminary positions and have a localized movement. This high-frequency dispersive region gives rise to ac conductivity. The NNH and VRH model [22,23] can be expressed as,where σ0 is a constant, signifies the phonon frequency, c is the fraction of sites occupied by polarons and electrons, r represents the average distance of hopping, α is the rate of decaying wave function, and Ea is the activation energy.
Study of the electrical and optical properties of Ge27Se58Pb15 chalcogenide glass
Published in Journal of Asian Ceramic Societies, 2018
Hukum Singh, K. S. Rathore, N. S. Saxena
Figure 4 shows the variation of dc electrical conductivity with temperature for Ge27Se58Pb15 glass. It is found that conductivity increases sluggishly upto 348 K and increases rapidly beyond 348 K. When temperature is increased from 303 to 348 K, charge carriers attains energy and conduction occurs through hopping of carriers in the localized states in the bands near the Fermi level. As the temperature is low, energy attained for conduction is also low. This is observed as slow increase in conductivity. But, when temperature crosses 348 K, the charge carriers become more mobile and conduction occurs through hopping of charge carriers in band tails. This leads to increase in conductivity as observed in Figure 4 in temperature range 348–423 K. Therefore, it is expected that conduction takes place by variable range hopping (VRH) in the lower temperature range 298–348 K while in higher temperature range, i.e. 348–423 K, conduction takes place via thermally assisted process.