The Temperature Dependence of the Electrical Conductivity of Polypyrrole Films Doped with Different Counterions (original) (raw)
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Electrical Conductivity of Polypyrrole Films at a Temperature Range of 70 K to 350 K
Materials Research Bulletin, 1998
The dc conductivity of electrochemically synthesized polypyrrole films doped from light to intermediate levels with p-toluene sulfonic acid was measured in the temperature range of 77 to 300 K, using a modified four-probe rig. Plots of dc conductivity vs. temperature were parameterized by fitting Mott's Variable Range Hopping conduction model. The localization length of localized electrons was assumed to be 3 Å, which is approximately equal to the length of a pyrrole monomer. Mott parameters of polypyrrole films doped with p-TS were evaluated at 300 and 10 K. Results were found to be consistent with Mott's requirement that ␣R Ͼ Ͼ 1. Microwave (10 GHz) conductivity measurements were carried out on the same set of polypyrrole samples at a temperature range of 90 to 473 K. Both microwave and dc conductivities were found to increase with temperature. The large values of microwave conductivity compared to dc conductivity over the temperature range tested suggests the existence of more charge hopping that does not contribute to the dc conductivity.
dc Conduction in electrochemically synthesized polypyrrole films
1998
DC conductivity measurements were performed by modified four-probe rig on electrochemically synthesized polypyrrole films at a temperature range of -30 • C to 120 • C. Conductivity increased with temperature. The temperature dependence of conductivity was very high for lightly doped polymers, decreasing as the doping level increased. The model used to describe the conduction process was the conduction model originally developed for amorphous silicon by Mott and Davis. When applied to conducting polymers, it assumes that electron transport originates from localized or fixed states within the polymer chain. The charge transfer between the chains takes place by hopping, referred to as phonon-assisted hopping, between two localized states. Plots of DC conductivity versus temperature can be parametrized by Mott's Variable Range Hopping conduction model. The DC conductivity of polypyrrole films doped from light to intermediate levels with p-toluene sulphonic acid were measured in the temperature range of 77K to 300K. The localization length of localized electrons was assumed to be 3Å, which is approximately equal to the length of the pyrrole monomer. Mott parameters of polypyrrole films doped with p-TS were evaluated at 300K and 10K. Results were found to be consistent with the Mott's requirement that αR >> 1 . Theoretical values of α and N (EF ) have been determined at approximately 10 8 cm −1 and 10 19 -10 20 cm −3 eV −1 , respectively. Hence according to Mott parameters determined by the experimental data for the p-TS doped polypyrrole samples, Mott parameters are seen to have a better agreement with those expected from disordered systems, particularly for lightly doped samples, indicating the suitability of Mott's model to these samples. The average hopping distance R decreased from 16Åto 4.4Åwith the increase in the doping level from 0.006 M to 0.03 M at 300K, whereas at 10K, R decreased from 37Å to 10Å over the same dopant range.
Evaluation of electrical conduction in iodine-doped polypyrrole
Journal of Materials Science, 1992
Electrical conductivity of polypyrrole has been measured after doping with different iodine concentrations. A thermally activated electrical conductivity was found which was pseudoohmic and increased with doping level. The results can also be fitted by log cr versus T -1/2 and tog o-versus T-1/4 dependences, instead of the Arrhenius log cr versus T -1 dependence. From these results it was concluded that within the experimental scatter no significant distinction can be made between these different temperature dependence laws. Hence these data can only enable one to speculate about the true underlying transport model, rather than to draw decisive conclusions. Electrical conductivity results predicting the role of iodine dopant concentration on the conduction process of semiconducting polypyrrole are discussed.
Solid State Communications, 2010
Polypyrrole was synthesized by the chemical oxidation method in the presence of phosphoric acid by varying oxidant to monomer molar ratio for the optimization of electrical conductivity. The conductivity in doped polypyrrole reached up to a maximum value of 9.18 S/cm. Granular morphology was observed in chemically synthesized polypyrrole. Neutralization of doped polypyrrole was done with aqueous ammonium hydroxide and three orders of reduced conductivity were obtained in neutral polypyrrole. Doped and undoped samples of polypyrrole were then electrically characterized over a wide temperature range of 10-300 K. The measured electrical conductivity rises with the increase in temperature and shows the semiconducting nature of the material. Strong and weak temperature dependence of conductivity was revealed by undoped and doped polypyrrole samples respectively. An effort has been made to explore the electrical transport in doped and undoped polypyrrole by charge transport models. The experimental data obeys Kivelson's hopping model in temperature range of 60-300 K and fluctuation assisted tunneling was the dominant conduction mechanism below 60 K.
Structure–conductivity relationships in chemical polypyrroles of low, medium and high conductivity
Synthetic Metals, 2006
Chemically synthesized polypyrroles of low (σ < 75 S/cm), medium (75 < σ < 200 S/cm) and high (σ > 200 S/cm) electrical conductivity (σ) with the same dopant and degree of doping have been investigated by means of Wide Angle X-ray Scattering (WAXS), 13 C Cross Polarized Magic Angle Spinning Nuclear Magnetic Resonance ( 13 C CP/MAS NMR) spectroscopy and Fourier Transform Infrared (FTIR) Spectroscopy to establish structure-conductivity relationships useful for industrial applications. A similar amorphous structure was found by WAXS even for the higher conducting PPy (σ = 288 S/cm). WAXS spectra for polypyrroles of medium and high conductivity showed a weak peak at 2θ = 10-11 • due to improved order of the counterions in these materials. The effect of the counterion size in the asymmetry of the PPy main WAXS peak was elucidated by performing ion exchange of the Cl − dopant with counterions of larger size such as BF 4 − and ClO 4 − . From 13 C CP/MAS NMR measurements predominantly ␣-␣ bonding was found in these materials. The main 13 C CP/MAS NMR resonance peak of PPy located at 126-128 ppm was broadened upon increasing conductivity. Interestingly, a linear relationship was observed between the half-width at half-height (HWHH) of the 13 C CP/MAS NMR peak and conductivity where a doubling of the polypyrrole conductivity leads to an increase of HWHH by 6-7 ppm. FTIR data of these materials were analysed in the framework of the Baughman-Shacklette theory describing the dependence of conductivity on conjugation length. By comparison of model predictions and experimental results, the PPy samples were found to be in the regime of long conjugation lengths, L K 2 /k B T, where K 2 is a parameter related to the energy change on going from j − 1 to j charges on a conjugated segment of conjugation length L, k B the Boltzman constant and T is the absolute temperature.
Electrical Properties of Polypyrrole Conducting Polymer at Various Dopant Concentrations
Polypyrrole conducting polymer was prepared by chemical reaction method with various concentrations of iron (III) chloride (FeCl3) as dopant. The dc conductivity was obtained from current-voltage characteristic by using parallel-plate techniques in the temperature range of 100-300K. With the involvement of chloride, Cl -in the polymeric chain, the conductivity increased as temperature and the dopant concentration increased. To describe the electrical transport process, Mott's 1-D, 2-D and 3-D variable range hopping (VRH) models have been considered. The result gives evidence of transport mechanism based on Mott's 3-D VRH mechanism for all various dopant concentrations studied.
Effects of Pressure and Temperature on Conductivity of Highly Dedoped Polypyrrole
2004
T he effects of uniaxial pressure parallel to the current and the effect of temperature on resistance of highly dedoped polypyrrole samples were investigated. Polypyrrole samples were prepared electrochemically at 0.87 V constant potential from acetonitrile solution in presence of perchlorate anion as dopant on the gold sputtered glass as working electrode. Polypyrrole samples were dedoped chemically in NH 3 for 1 h. Because of high resistance of polymer samples, the two-point probe technique could be applied for resistance measurements. Conductance of these highly dedoped polymers increases with pressure and temperature exponentially according to the Mottvariable range hopping theory (VRH). Change in the efficient number of states and also volume of the polymer due to the pressure can cause increases in the density of states near the Fermi level. Pressure should bring about an increase of orbital overlap, especially between the electron-rich of the neighbouring molecules. This increase of electron orbital overlap should be expected to increase the ease of inter-molecular electron transfer, by decreasing the distance and energy barriers to diffusion and tunnelling and by increasing the chain-chain areas of contact, thereby increasing the probability for electron transfer. So, the number of states that electron can hop from it would increase. With respect to the presence of numerous vacancies in highly dedoped polymer samples, a modified VRH model is introduced to fit the observed data based on the decreasing in polymer volume and increasing in the efficient number of states that electron can hop from it. Effects of Pressure and Temperature on Conductivity of Highly Dedoped Polypyrrole polypyrrole; conductivity; pressure; temperature; variable range hopping.
Isotherms of the imaginary part of the permittivity from 10 −2 to 2 10 6 Hz from liquid nitrogen to room temperature for fresh and thermally aged specimens of conducting polypyrrole reveal a dielectric loss peak, which is affected by the reduction of conducting grains with aging. Charge trapping at the interfaces separating the conductive islands seems invalid. Thermal aging indicates that macroscopic conductivity and short range one have different aging evolution. The first dc conductivity is dominated by the tunneling of the carriers between neighboring grains through the intermediate insulating barriers, though the second ac conductivity is due to a backward-forward movement of the carriers and is controlled by the intrachain transport of them and their hopping between the chains.
Electrical Transport and Magnetoresistance of Doped Polypyrrole
2015
56 www.ijeas.org Abstract— Different doped samples of conducting polypyrrole (PPy) are prepared electrochemically at different current densities. The electrical transport of conducting polypyrrole is investigated in a wide range of temperature starting from 4.2 K to 300 K. It is observed that, for samples prepared at high current densities, the electrical conduction is dominated mainly by the mechanism based on variable range hopping in a wide temperature range. On the other hand, the magnetoresistance of polypyrrole is investigated in the temperature range from 1.2 K to 4.2 K and magnetic field from H=0 T to H= 10.3 T. It is observed that, PPy sample is characterized by large positive magnetoresistance. This obtained large positive magnetoresistance in the insulating regime is typically expected for VRH conduction.
Electronic Conduction in Polymers. I. The Chemical Structure of Polypyrrole
Australian Journal of Chemistry, 1963
The pyrolysis of tetraiodopyrrole in an inert atmosphere at temperatures from 120-700� yields black, infusible, amorphous polymers insoluble in solvents. Depending on the pyrolysis temperature, iodine may be present in the polymers as iodine of substitution and as chemisorbed molecular iodine, which is very tenaciously held. As a first approximation, the structure may be regarded as a three-dimensional network of pyrrole rings cross-linked in a nonplanar fashion by direct carbon to carbon linkages. The secondary nitrogen atoms form a hydroquine type system which may be oxidized by iodine or molecular oxygen under alkaline conditions. The extent of oxidation depends on the hydroxyl ion concentration. The nonplanarity of the oxidized quinonoid system renders it unstable but stability is enhanced, as in the triphenylmethane dyestuffs, by the formation of a carbinol. Despite their nonplanarity polypyrroles are relatively good conductors of electricity. The resistivity ranges from 1-200 ...