Study of the Glass System, (100 − x)(3K2S − 7P2S5) − xKI (x = 0, 5, 10, 15, and 20) for K+ Ion Conductivity

A series of glassy electrolytes in the ternary system (100 − x)(3K2S − 7P2S5) − xKI (x = 0, 5, 10, 15 and 20) was investigated, with a focus on their potassium-ion conductivity using electrochemical impedance spectroscopy (EIS). Among the compositions studied, the electrolyte with x = 20 exhibited the highest ambient-temperature conductivity, measured at 2.36 𝗑 10−10 S∙cm−1. The materials were characterized by XRD, DSC, and Raman spectroscopy. DSC results revealed glass transition temperatures just above 130˚C; therefore, temperature-dependent conductivity measurements were performed within the range of 21˚C - 125˚C to determine activation energies without interference from thermal transitions. Raman spectroscopic analysis confirmed the presence of invariant structural units of the network former— PS 4 3− , PS 7 4− , PS 6 4− —across all glassy electrolytes. The similarity of vibrational modes to those of the parent composition indicates that halide ions do not interact chemically with these network-forming units. Instead, the halide ions occupy interstitial sites within the glass structure. The observed increase in ionic conductivity with higher KI content is attributed to a rise in charge carrier concentration, consistent with the interstitial incorporation of halide ions without disrupting the anionic framework.