Influence of NaI Additions on the Electrical, Dielectric, and Transport Properties in the GeS2–Ga2S3–NaI Glass System

Abstract

The vitreous system GeS₂–Ga₂S₃ can incorporate a large amount of alkali salts, for example NaI, and such materials have a potential to be used as solid electrolytes for all-solid-state batteries. The present work focuses on the effects of NaI addition in the (GeS₂)_x(Ga₂S₃)_{100 –x} glass matrix, where x = 65, 72, 80, and 88. AC and DC electrical and dielectric properties were measured in the temperature range from 20 up to 200°C and in the frequency range 1 Hz–100 kHz, in air, at different temperatures by steps of 1°C. The values of electrical conductivity significantly increase with increasing of NaI content. The DC conductivity values 2.5 × 10^–4 S m^–1 at room temperature were detected for glasses with 25 and 30 mol % of NaI in (GeS₂)₇₂(Ga₂S₃)₂₈ and with 30 mol % NaI in (GeS₂)₆₅(Ga₂S₃)₃₅ matrices. Samples with NaI concentration higher than 20 mol % show a poor stability against moisture. In order to improve their stability the glass composition was modified by addition of 2.5 mol % P₂S₅ in the system. The activation energy values slightly decrease with NaI content. The GeS₂/Ga₂S₃ ratio and P₂S₅ addition to the glass matrix have low effect on transport properties. The DC conductivity, electrical relaxation, and depolarization mechanisms are similar. Electrical charge transfer is connected with hopping of Na⁺ ions or reorientation of dipoles containing these ions.