Hopping frequency and conductivity relaxation of promising chalcogenides: AC conductivity and dielectric relaxation approaches

Abstract

Ag2S doped chalcogenide glassy systems have been characterised on the basis of AC conductivity and electric modulus formalism. Various nanophases such as Ag2Se, Te0.5 Se3.5 etc. and dislocation (defects) have been identified and their roles in the conduction process have been established. XRD analysis provides that incorporation of more Ag2S content in the present system should play important role to enhance the dislocation and to decrease the crystallite sizes. The Fourier transform infrared spectra (FT-IR) confirm the characteristic vibration of Ag-S at 500-650 cm-1, stretching vibrations of the O-H bond near 3400 cm-1 and bending vibrations of the adsorbed H2O molecules on the surface of Ag2S near 1600 cm-1. Composition dependent optical phonon frequency (ν0) and Debye temperature (θ D) have been estimated from FT-IR and it is noteworthy that θ D increases with Ag2S content in the compositions up to x = 0.1, but decreases for x = 0.2. This result suggests higher kinetic energy of the constituent atoms/molecules, which may refer to higher electrical conductivity due to polaron hopping. Correlated barrier hopping (CBH) model in its modified version has been found most suitable model to explore the conduction mechanism. Short time relaxation process may be considered to be trivially associated with conduction of polaron. universal scaling approach proposed by Ghosh and Pan has been adopted to interpret electrical relaxation process from time-temperature superposition principle. AC conductivity spectra at various temperatures exhibit a perfect overlap into a single master curve. This feature must be an indication of the temperature independent relaxation process. On the other hand, conductivity spectra of all the compositions at a particular temperature do not exhibit perfect overlapping into a single master curve. This result indicates that the relaxation dynamics of charge carriers (polarons) is strongly dependent on compositions.