Study of dielectric relaxation and thermally activated a.c. conduction in glassy Se₇₀Te₃₀ and Se₇₀Te₂₈M₂ (M = Ag, Zn and Cd) alloys

A detailed study of conduction mechanism of glassy Se70Te30 and Se70Te28M2 (M = Ag, Zn and Cd) alloys has been carried out in terms of dielectric properties and a.c. conductivity. Temperature and frequency dependent dielectric constant, dielectric loss and σac for the same system were measured in the frequency spectrum, 1 kHz to 1 MHz and temperature range, 303–338 K. The a.c. conductivity (σac) is found to be proportional to ωs (s < 1). The temperature dependence of both a.c. conductivity and frequency exponent (s) is reasonably well interpreted by the correlated barrier hopping (CBH) model. We showed that the bi-polaron hopping is dominant over the potential barrier and estimated the density of defect states (DOS) at 10 kHz. We found a good agreement between bi-polaron conductivity and experimental results.