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

In this study, Ag2S samples are characterizedusingX-ray diffraction, X-ray photoelectron spectroscopy, differentialscanning calorimetry, and impedance spectroscopy. At 447 K, an ACconductivity jump of about two orders of magnitude is observed, andan endothermic peak is measured by differential scanning calorimetry,apparently resulting from the beta-to-alpha phase transition,i.e., the order-disorder transition. A silver vacancy proportionof 2.2% is obtained by refinement of the X-ray diffraction profile.The dielectric loss peaks and analysis of the observed complex impedancepeaks indicate four different relaxation processes, namely, P-1, P-2, P-3, and P-4, from lowto high temperature. P-1 and P-2 are obviouslythe migration of silver ions from two types of lattice sites to theirnonequivalent nearest-neighbor vacancies. P-3 involves themigration of interstitial silver ions to adjacent interstitial sites.An Arrhenius-to-VFTH crossover of the P-4 relaxation timeis inferred to the hopping of the individual silver ion and then thecooperative jumps of several ions in the disordered region of thesilver sublattice upon heating.