Variable range hopping mechanism

Arsenic pentafluoride effects a Friedel-Crafts chain extension and cross-linking in PPV. The electrical conductivity takes place by a variable-range hopping mechanism. 

The charge transport properties in the direction of free-carrier motion in a restricted-dimensional system have inportant consequences for the magnetotransport effects. This is treated in Sect. 5.3.4. For disordered systems, when the Mott variable-range hopping mechanism [3.58] dominates the conductivity, the temperature scaling law depends on the dimensionality the 3-D conductivity <73-0 varies with temperature following the law log (T3.D a T, whereas the 2-D conductivity varies as log (T2-D The transition from 3-D to 2-D behav-... 

Fig. 5.3 -9 Plot of the experimental power-law dependence of the conductivity on temperature for films of amorphous Ge of various thicknesses d. The transition from a 3-D (7 -i/4) behavior (region marked as slope) to a 2-D (7 -i/3) behavior (region marked as slope), as expected for the variable-range hopping mechanism, is clearly observed d = 500K (vertical bar). (After [3.54])...

The low temperature results indicate that a metal-insulator (or semiconductor) transition takes place at 30 K for PT and 10 K for PMT [546]. The temperature dependence of the electrical conductivity corresponds to the three-dimensional variable range hopping mechanism [485]. The temperature dependence of charge mobilities in PATs (n = 4,6, 8, 12) exhibits a local maximum immediately after the end of the glass transition region, which can be attributed to the transition of soft conformons (conformational defects) in the disordered phase to localized conformons [494]. 

When treated with Ij vapor, the reduced segments are oxidatively doped to the conducting state. Figure 5 presents the results of the electrical conductivity temperature dependence as a function film oxidation level prior to doping. The room temperature conductivity of the R = 0.00 film doped with 1.0 M HCl was measured to be 0.22 S/cm. With increasing R, the conductivity of the Ij doped films increases, and can be interpreted in terms of the quasi-lD variable range hopping mechanism (Equation 3) [16,14]... 

Singh and Narula [716] investigated ex situ correlations between the concentration of free spins and the dc conductivity as a function of temperature for electropolymerized PPy and some substituted PPys. The obtained parameters support a variable range hopping mechanism of conduction. An almost symmetrical line with Lorentzian shape was observed. 

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