engleski

INFLUENCE OF DISORDER ON VARIABLE-RANGE-HOPPING EXPONENTS IN HCL – DOPED POLYANILINE PELLETS

Polyaniline is a conjugated polymer that exhibits a finite electrical conductivity when doped by a protonic acid. In our work, we have studied the influence of doping by HCl on the conducting properties of pressed polyaniline pallets. Generally, polyaniline samples constitute a three-dimensional network (3D) of one-dimensional (intrachain) conductors. If the interchain coupling is sufficiently strong in comparison to the intrachain mean backscattering time, the system can be effectively regarded as a 3D one. Furthermore, if the Coulomb interaction between an excited electron and the corresponding hole is not completely screened, it should be taken into account in addressing the nature of the charge transport. Since polyaniline samples possess a high degree of structural disorder, the charge propagation occurs by variable-range-hopping mechanism. In our own-made samples we have found that increase of the doping not only enhances the electrical conductivity but also weakens the structural disorder, which affects the variable-range hopping. This is revealed in the temperature dependence of conductivity σ (T)=σ 0exp[-(T0/T)α ], where α and T0 contain information on the underlying physics. At low temperatures (below 200 K), α undergoes a significant change at the doping level Y=[Cl]/[N] 0.3, i.e., 60% of the full doping (Y=0.5): α =1/2 for lower doping, whereas more-doped samples exhibit α =2/5. [1] The obtained low temperature results can be well explained by the recent variable-range-hopping theory of Fogler, Teber and Shklovskii [2]. The same theory also applies above T 200 K where α =1/4 regardless of the doping level. Other relevant features, such as the charge localisation length (~2 nm) and the level of disorder, are inferred from magnetoconductivity and X-ray diffraction measurements, respectively. References [1] M. Novak, I. Kokanović, D. Babić, M. Baćani and A. Tonejc, Submitted, 2008 [2] M. M. Fogler, S. Teber and B. I. Shklovskii, Phys. Rev. B. 69, 035413 (2004)

doped polyaniline; electrical conductivity; hopping transport

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