Tailoring of dielectric behavior and a.c. conduction in binary Se80Te20 glass by incorporation of transition metals (Fe, Co, Ni, Cu)

Abstract

Transition metals (TMs) iron, cobalt, copper, and nickel have been chosen as the chemical modifiers with a binary alloy Se₈₀Te₂₀ as the parent sample to make novel Se₇₈Te₂₀TM₂ (TM = Fe, Co, Ni, Cu) alloys. The frequency dependence of dielectric loss and a.c. conductivity (\({\sigma }_{ac})\) have been studied and the possible mechanism has been checked. The dielectric constant (ε') shows significant variation among the samples, with the parent Se₈₀Te₂₀ alloy exhibiting the highest value, followed closely by Se₇₈Te₂₀Cu₂. Conversely, Se₇₈Te₂₀Fe₂ and Se₇₈Te₂₀Ni₂ alloys exhibit much lower values. The dielectric loss also varies widely, with Se₈₀Te₂₀, while Se₇₈Te₂₀Fe₂ and Se₇₈Te₂₀Ni₂ alloys present extremely low values of loss. The barrier height ranges between 0.31 eV (Fe-doped sample) and 1.2 eV (Ni-doped sample), indicating that doping influences the band gap significantly. The hooping distance shows considerable differences, with Fe-doped alloys exhibiting the highest value at 39.5 Å, while Co-doped samples show the lowest at 11.4 Å. Applicability of the Meyer-Neldel rule is observed in the a.c. conduction for all samples. The reducing nature of the power-law exponent “s” with increasing temperature indicates the correlated barrier hopping model for Se₈₀Te₂₀ and Se₇₈Te₂₀TM₂ (TM = Co, Ni, Cu) alloys, as they exhibit a certain nature of variation. However, because “s” increases with temperature, the non-overlapping small polaron tunneling model is a particularly appropriate mechanism for a.c. conduction of ternary Se₇₈Te₂₀Fe₂ alloy. Furthermore, we estimated the density of localized states for the synthesized material at various temperatures. The maximum reduction in the density of states is observed for the iron-containing parent sample.