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

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 degrees C and in the frequency range 1 Hz-100 kHz, in air, at different temperatures by steps of 1 degrees C. The values of electrical conductivity significantly increase with increasing of NaI content. The DC conductivity values 2.5 x 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 theseions.