An insight into the localization of charge carriers in conducting polyaniline by analyzing thermally stimulated depolarization signals A.N. Papathanassiou a, * , I. Sakellis a , J. Grammatikakis a , S. Sakkopoulos b , E. Vitoratos b , E. Dalas c a Section of Solid State Physics, Department of Physics, University of Athens, Panepistimiopolis, GR 15784 Zografos, Athens, Greece b Department of Physics, University of Patras, GR 265 00 Patras, Greece c Department of Chemistry, University of Patras, GR 265 00 Patras, Greece Received 2 September 2002; accepted 22 October 2002 by M. Cardona Abstract A dielectric relaxation mechanism, which is attributed to the localized motion of trapped polarons, has been recorded in conducting polyaniline by employing the thermally stimulated depolarization current technique. The signal was analyzed within the frame of the normal distribution in the activation energy value. The experimental dielectric relaxation results were manipulated in order to evaluate the length of the jump distance that the trapped polarons transfer along and the concentration of trap centers. The concentration of trapped carriers is calculated from two different viewpoints: the pair approximation that assumes phonon-assisted tunneling through the barrier separating two adjacent sites and the pinning model that considers the trapped polaron oscillating around its pinning point. Both models provide compatible results. q 2003 Elsevier Science Ltd. All rights reserved. PACS: 77.22.Ej; 77.22.Gm; 72.80.Le; 73.61.Jc Keywords: A. Disordered systems; A. Polymers; D. Dielectric response; D. Electronic transport 1. Introduction Conducting polyaniline is a promising polymer for technological applications, such as, electromagnetic shield- ing, anti-static coating, solid-state batteries, solar cells, electronic devices non-linear optics, etc. The electronic transport in conducting polymers has been the subject of theoretical and experimental investigation [1]. However, traps affect the electric charge transport in amorphous solids. A portion of the transferring entities is impeded within the bulk and is capable of performing localized motion. The application of an external electric field produces both dc conductivity and polarization (capaci- tance) phenomena. Preliminary investigations concerning the dielectric response of polyaniline, which is one of the representatives of the conducting polymers, protonated after treating with HCl showed that the presence of Cl 2 at redox centers results in the spatial localization of polarons [2,3]. The result is an increase of the dielectric constant. In a recent work, we showed that the thermally stimulated depolarization current (TSDC) technique performed with blocking electrodes is capable of tracing the polarons’ capture in deep traps. The scope of the present paper is to examine how the analysis of the TSDC signal or dielectric relaxation results can provide information in microscopic scale about the earlier-mentioned phenomenon. 0038-1098/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved. PII: S0038-1098(02)00707-X Solid State Communications 125 (2003) 95–98 www.elsevier.com/locate/ssc * Corresponding author. Tel.: þ30-107-224-444; fax: þ 30-107- 661-707. E-mail address: apapathan@in.gr (A.N. Papathanassiou).