Structural Evolution and AC Conductivity of Ag+ Doped Chalcogenide System: Explanation Using DFT

Abstract

The system of chalcogenides, represented as (Ag2S)x − (0.2 Zn − 0.3Te − 0.5Se)1‐x for x values of 0.0, 0.1, and 0.3, has been developed. As the content of Ag2S in the system increases, there is a corresponding change in the size of various nanocrystallites, including Ag2S, Te, and Se. Additionally, the formation of new phases resulting from their combinations has become evident. This behavior may lead to potential structural modifications in the studied system. The dynamic nature of conductivity suggests that the origin of the Meyer‐Neldel energy (MNE) arises from polaron hopping through various traps due to multi‐phonon excitations. A modified version of the Correlated Barrier Hopping (CBH) model has been identified to predict the conduction paths of polarons (charge carriers) in pairs, facilitated by current transfer among localized sites at the Fermi level. A larger HOMO‐LUMO gap is likely to provide a greater resistance path for polaron conduction, which is supported by density functional theory (DFT) studies. A schematic conduction model has been proposed to explain the nature of electrical conductivity in the current system. The rate of crystallization and nucleation may depend on the difference between glass transition temperature (Tg) and crystallization temperatures (TCM), which are estimated from differential scanning calorimetric study.