variable range hopping
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Polymers ◽  
2022 ◽  
Vol 14 (2) ◽  
pp. 269
Author(s):  
Antonio J. Paleo ◽  
Beate Krause ◽  
Maria F. Cerqueira ◽  
Enrique Muñoz ◽  
Petra Pötschke ◽  
...  

The temperature dependent electrical conductivity σ (T) and thermopower (Seebeck coefficient) S (T) from 303.15 K (30 °C) to 373.15 K (100 °C) of an as-received commercial n-type vapour grown carbon nanofibre (CNF) powder and its melt-mixed polypropylene (PP) composite with 5 wt.% of CNFs have been analysed. At 30 °C, the σ and S of the CNF powder are ~136 S m−1 and −5.1 μV K−1, respectively, whereas its PP/CNF composite showed lower conductivities and less negative S-values of ~15 S m−1 and −3.4 μV K−1, respectively. The σ (T) of both samples presents a dσ/dT < 0 character described by the 3D variable range hopping (VRH) model. In contrast, their S (T) shows a dS/dT > 0 character, also observed in some doped multiwall carbon nanotube (MWCNT) mats with nonlinear thermopower behaviour, and explained here from the contribution of impurities in the CNF structure such as oxygen and sulphur, which cause sharply varying and localized states at approximately 0.09 eV above their Fermi energy level (EF).


Materials ◽  
2021 ◽  
Vol 14 (24) ◽  
pp. 7689
Author(s):  
Gad Koren ◽  
Anna Eyal ◽  
Leonid Iomin ◽  
Yuval Nitzav

Nickelate films have recently attracted broad attention due to the observation of superconductivity in the infinite layer phase of Nd0.8Sr0.2NiO2 (obtained by reducing Sr doped NdNiO3 films) and their similarity to the cuprates high temperature superconductors. Here, we report on the observation of a new type of transport in oxygen poor Nd0.8Sr0.2NiO3−δ films. At high temperatures, variable range hopping is observed while at low temperatures a novel tunneling behavior is found where a Josephson-like tunneling junction characteristic with serial resistance is revealed. We attribute this phenomenon to coupling between superconductive (S) surfaces of the grains in our Oxygen poor films via the insulating (I) grain boundaries, which yields SIS junctions in series with the normal (N) resistance of the grains themselves. The similarity of the observed conductance spectra to the tunneling junction characteristic with Josephson-like current is striking, and seems to support the existence of superconductivity in our samples.


2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Adithya Jayakumar ◽  
Viney Dixit ◽  
Sarath Jose ◽  
Vinayak B. Kamble ◽  
D. Jaiswal-Nagar

AbstractWe report a systematic investigation of the differences in charge transport mechanism in ultra-thin nano-island like films of palladium with thickness varying between 5 nm and 3 nm. The thicker films were found to be metallic in a large temperature range with a dominant Bloch–Grüneisen mechanism of charge transport arising due to electron-acoustic phonon scattering. These films were also found to exhibit an additional electron–magnon scattering. At temperatures below 20 K, the two films displayed a metal-insulator transition which was explained using Al’tshuler’s model of increased scattering in disordered conductors. The thinner films were insulating and were found to exhibit Mott’s variable range hopping mechanism of charge transport. The thinnest film showed a linear decrease of resistance with an increase in temperature in the entire temperature range. The island-like thin films were found to display very different response to hydrogenation at room temperature where the metallic films were found to display a decrease of resistance while the insulating films were found to have an increase of resistance. The decrease of resistance was ascribed to a hydrogen induced lattice expansion in the thin films that were at the percolation threshold while the resistance increase to an increase in work function of the films due to an increased adsorption of the hydrogen atoms at the surface sites of palladium.


Author(s):  
Iqbal Quasim

The present paper reports the electrical properties of pure and sodium modified copper tartrate single crystals. Single crystal growth of these materials followed by their characteristics has already been published somewhere else. Having achieved the growth of pure and sodium modified copper tartrate single crystals and established their basic characteristics, it is thought worthwhile to have an understanding of their electrical properties and their modification on replacement of some copper ions in the lattice of copper tartrate by sodium ions. The electrical properties are studied by measuring electrical conductivity in the temperature range from 80 to 300 K. The study reveals that conductivity is a function temperature in these crystals. Moreover both pure and modified copper tatrate single crystal are semiconducting but the conductivity of pure modified copper tatrate single crystal is more than that of pure a copper tatrate single crystal. The results have been explained in terms variable range hopping model.


2021 ◽  
pp. 2100340
Author(s):  
Miguel Ortuño ◽  
Francisco Estellés-Duart ◽  
Andrés M. Somoza

Nanomaterials ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 2678
Author(s):  
Dan Shan ◽  
Daoyuan Sun ◽  
Mingjun Tang ◽  
Ruihong Yang ◽  
Guangzhen Kang ◽  
...  

Recent investigations of fundamental electronic properties (especially the carrier transport mechanisms) of Si nanocrystal embedded in the amorphous SiC films are highly desired in order to further develop their applications in nano-electronic and optoelectronic devices. Here, Boron-doped Si nanocrystals embedded in the amorphous SiC films were prepared by thermal annealing of Boron-doped amorphous Si-rich SiC films with various Si/C ratios. Carrier transport properties in combination with microstructural characteristics were investigated via temperature dependence Hall effect measurements. It should be pointed out that Hall mobilities, carrier concentrations as well as conductivities in films were increased with Si/C ratio, which could be reached to the maximum of 7.2 cm2/V∙s, 4.6 × 1019 cm−3 and 87.5 S∙cm−1, respectively. Notably, different kinds of carrier transport behaviors, such as Mott variable-range hopping, multiple phonon hopping, percolation hopping and thermally activation conduction that play an important role in the transport process, were identified within different temperature ranges (10 K~400 K) in the films of different Si/C ratio. The changes from Mott variable-range hopping process to thermally activation conduction process with temperature were observed and discussed in detail.


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