Conducting polymer composites of polyaniline/vanadium pentaoxide PANI/V2O5 (with different initial weight percentage of V2O5) has been synthesized by in situ polymerization method. DC conductivity of compressed pellets has been analyzed in the temperature range 300–550？K and was found to increase with V2O5 doping. This increase in conductivity is mainly due to band conduction. It has also been observed that the dielectric constant and dielectric loss increase with the level of doping of V2O5 but remain independent of the frequency (50？KHz–1？MHz). X-ray diffraction pattern shows some order of crystallinity of composites due to interaction of polyaniline with V2O5. UV-visible spectroscopy shows an increase in the optical band gap with doping. 1. Introduction The conducting polymers have emerged as a new class of materials because of their unique electrical, optical, and chemical properties. By proper doping the conductivity of these materials can be varied from semiconducting to metallic regime, which offers new concept of charge transport mechanism. Among different conducting polymers, conductive polyaniline (PANI) has been studied extensively because of its ease of synthesis in aqueous media, its environmental stability, special electrical, and other properties. PANI and its derivatives have received much attention because of their various technological applications, reversible proton doping, high electrical conductivity, and ease of bulk synthesis. PANI is also a suitable candidate for a variety of technological applications such as solar cells, electromagnetic shielding, electrodes for rechargeable batteries, and sensors [1–11]. Many authors have studied the progress of chemical polymerization and doping of aniline and its derivatives. The effort was to correlate mechanisms of oxidation of anilines and properties of PANI such as electrical conductivity, molecular weight, and crystallinity. However, when they were taken in the composite form, their electrical as well as dielectric properties alter from those of basic materials. A number of groups had reported on the electrical conductivity and dielectric properties of composites of a variety of conducting polymers [12–15]. Recently heterogeneous conducting polymer composites, especially organic-inorganic composites, became the subject of extensive study. Among the base materials used, polyaniline (PANI) is one of the most extensively studied conducting polymer. Ever since its discovery in a pioneering work by Mc Diarmid et al. [16–21]. The DC conductivity of a conjugated polymer depends on the doping
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