An investigation of S–Se–Te semiconducting glassy alloys: Structural characterization and electrical conductivity

Abstract

A sequence of chalcogenide glassy alloys, xS-(1-x) (0.5Te-0.5Se) for x = 0.1, 0.14, 0.24 and 0.34 have been prepared using well-established melt quenching method. The XRD patterns reveal the existence of crystallinity, superimposing over the amorphous glassy matrix. The effects of increasing values of mean crystallite size and optical band gap energy with composition cause electrical conductivity to reduce. The DC conductivities of the present system have been explored using Mott and Greaves's variable range hopping model. The values of temperature dependent small polaron hopping distance (Rhop) and hopping energy (Whop) are in agreement with the nature of DC conductivity. The anomaly of the sample for x = 0.14 may arise due to the lesser number of localized or defect states within the mobility gap and higher values of small polaron hopping distance and average hopping energy. The well-known Meyer-Neldel rule, Jonscher's Universal power-law and Almond-West formalism have been employed to investigate the AC conductivity spectra. The reducing nature of power-law exponent (s) with increasing temperature of the samples for x = 0.1 and 0.14 indicates that correlated barrier hopping (CBH) model is the best model for AC conduction mechanism. On the other hand, non-overlapping small polaron tunneling (NSPT) process is the suitable AC conduction mechanism of the samples for x = 0.24 and 0.34 due to the increasing nature of s with temperature. The conductivity scaling signifies temperature independency and composition dependency of electrical relaxation process.