Effects of the Se substitution for Te on the structure and properties of glasses in the Ag30As28(SexTe100-x)42 system

Abstract In this work, series of glass samples in the Ag30As28 (SexTe100-x)42 (x = 15, 30, 50, 70, 85) system are prepared. Effects of the Se/Te ratio on density (ρ), glass transition temperature (Tg), room-temperature conductivity (σ298k) and crystallization behaviors of glasses are investigated, and their associations with the structure of glasses are discussed. Results show that with the increased substitution of Se for Te, the molar volume (Mv) decreases and Tg increases, indicating the increased space packing efficiency and the enhanced structure connectivity. The strengthened structure leads to an abnormal increase of ρ when x is lower than 30 mol%. Further increase of the Se/Te ratio results in the reduction of ρ due to the dominant effect of smaller molar weight (Mw). The σ298k of glasses decreases with Se increasing from 15 to 50 mol%, and then interestingly increases up to the level even higher than that of the sample with the lowest Se content (15 mol%). Raman spectra shows the transformation of main glass structure units from Te-based pyramids to Se-based complexes as the Se/Te ratio increases. According to XRD patterns of samples thermally treated at either lower (215 °C) or higher (265 °C) temperature, with the Se/Te ratio increasing, the dominant precipitated crystals suffer an evolution from AsTe to Ag2Te and finally to the AgAsSe2 semiconductor phase, consistent with the variation trend of Raman spectra. In terms of the structural similarity principle, we thus suppose that the formation of structural units similar to AgAsSe2 semiconductor crystals inversely increases the conductivity of glasses, realizing the mutual benefits of the improved thermal stability and increased conductivity of chalcogenide glasses.