Ag-Ion Dynamics in the Low-Temperature Form of Ag2S as Studied by Impedance Spectroscopy

Abstract

In this study, Ag2S samples are characterized using X-ray diffraction, X-ray photoelectron spectroscopy, differential scanning calorimetry, and impedance spectroscopy. At 447 K, an AC conductivity jump of about two orders of magnitude is observed, and an endothermic peak is measured by differential scanning calorimetry, apparently resulting from the β-to-α phase transition, i.e., the order–disorder transition. A silver vacancy proportion of 2.2% is obtained by refinement of the X-ray diffraction profile. The dielectric loss peaks and analysis of the observed complex impedance peaks indicate four different relaxation processes, namely, P1, P2, P3, and P4, from low to high temperature. P1 and P2 are obviously the migration of silver ions from two types of lattice sites to their nonequivalent nearest-neighbor vacancies. P3 involves the migration of interstitial silver ions to adjacent interstitial sites. An Arrhenius-to-VFTH crossover of the P4 relaxation time is inferred to the hopping of the individual silver ion and then the cooperative jumps of several ions in the disordered region of the silver sublattice upon heating.