Transition of charge transport phenomena from 3D to 1D hopping at low temperatures in polyaniline/graphene composites

Abstract

Here, we present the charge transport properties of polyaniline/graphene composites prepared by a chemical oxidation method in the presence of four different loading concentrations (2, 4, 6, and 8 wt. %) of graphene. The synthesized materials are characterized for surface and chemical bonding analyses through field-emission scanning electron microscopy and Fourier transform infrared spectroscopy techniques, respectively. The change in the chemical structure of the prepared composites with graphene loading concentrations revealed the possible increment in electrical conductivity. The room-temperature dc conductivity of the prepared composites was found to increase from ∼22 to 217 S/cm with an increase in the loading concentration of graphene from 2 to 8 wt. %. The temperature-dependent electrical conduction behavior of the prepared samples is investigated under Mott's variable-range hopping conduction mechanism. It is found that all composite samples follow three-dimensional (3D) hopping in the higher temperature region (>44 K), which transforms into one-dimensional (1D) hopping at lower temperatures (<44 K). A decrease in hopping distance (1.07–0.96 nm) and an increase in density of states (3.20 × 1021–4.95 × 1021 cm−3 eV−1) in three dimensions with an increase in the graphene loading concentration from 2 to 8 wt. % suggest the requirement of lower hopping energy (61.3–55.5 meV) for conduction. The estimated hopping parameters also revealed a nonadiabatic small-polaron hopping conduction mechanism that is followed by the charge carriers in the present samples for both one- and three-dimensional variable range hoppings.