Mechanism of direct current electrical charge conduction in p-toluenesulfonate doped polypyrrole/carbon composites

Abstract

Polypyrrole/carbon (PPy/C) composites have been synthesized using varying concentration of p-toluenesulfonate (pTS) dopant by surface initiated in-situ chemical oxidative polymerization. The synthesis and influence of pTS on the structure of the PPy/C composites are confirmed by Fourier transform infrared studies and the morphological features have been examined by scanning electron microscopy. X-ray photoelectron spectroscopy, employed to examine the surface composition and doping level of these composites, confirms the anionic doping into the polymer backbone. Electron spin resonance measurement has been carried out on these samples to identify the nature of the charge carriers and their concentration at different doping levels. The dc electrical conductivity of these composites has been measured in the temperature range ∼10–305 K. The observed results have been analyzed in the framework of existing theoretical models. Different Mott's parameters, such as characteristic temperature (T0), density of states at the Fermi level {N(EF)}, average hopping distance (R), and average hopping energy (W), evaluated from dc conductivity data supports the applicability of Mott's three dimensional variable range hopping mechanism in this system.

Charge transport mechanism of thermally reduced graphene oxide and their fabrication for high performance shield against electromagnetic pollution

“…The charge transport between the highly conductive intra-graphitic domains or inter-graphitic domains separated by lower conductive region is explained on the basis of variable range hopping conduction. In the case of strong localization of charge carriers, hopping will take place via jumping of electrons to the nearest neighbor sites, but for the weaker localization the conduction takes place through variable range hopping via jumping of electrons to the far away sites of lower activation energy near Fermi level [51,52]. To analyse the dimensionality of hopping of charge carriers, the measured dc conductivity has been plotted as a function of T À1/2 , T À1/3 and T À1/4 ( Fig.…”

Effect of helium gas pressure on dc conduction mechanism and EMI shielding properties of nanocrystalline carbon thin films

“…The pre-exponential factor (s o ) and the characteristic temperature (T o ) are the functions of density of states and localization length. These parameters determine the thermally activated hopping between the localized states of different energies and can be evaluated from the intersection of conductivity (s dc ) axis and the slope, respectively [28]. Thus, the deposited nanocrystalline carbon films follow the VRH conduction mechanism for the charge transport between the highly conductive intra-nanocrystallites or internanocrystallites sites separated by the lower conductive amorphous regions.…”

“…It has been observed that the values of the activation energy for all the samples increase with the increase of temperature and decrease with the increase of s dc or helium partial pressure which further suggests the hopping conduction behavior of the samples. The behavior of temperature dependent activation energy can be further explained on the basis of Holstein's multiphonon model [28,36,37]. Though, in the low temperature region, these multiphonon processes are replaced by the single optical phonon absorption/emission process and the activation energy can be given as: …”

“…Thus, the deposited nanocrystalline carbon films follow the VRH conduction mechanism for the charge transport between the highly conductive intra-nanocrystallites or internanocrystallites sites separated by the lower conductive amorphous regions. For the strong localization of charge carriers, hopping will take place via jumping of electrons to the nearest neighbor sites, but for the weaker localization the conduction takes place through VRH via jumping of electrons to the far away sites of lower activation energy near the Fermi level [28].…”

“…The nanocrystallites are randomly distributed and trapped by the amorphous regions which discarded the simple band conduction mechanism for charge transport. The band conduction mechanism has been further ruled out by the temperature dependent activation energy which is calculated by the expression [28].…”