Mutual effects of Ag doping and non-stoichiometric glass forming units on the structural, thermal, and electrical properties of Ag30+xAs28-xSe21Te21 chalcogenide glasses

Abstract In this work, we report the sensitivity of structural, thermal, and electrical properties of Ag30+xAs28-xSe21Te21 (x = 2, 4, 6, 8, 10) chalcogenide glasses to the relative abundance of Ag and As in the compositions. The results show non-linear variation of glass density with linear increase in Ag (or decrease in As), implying structural change at 38 at.% Ag (or 20 at.% As). This structure change was further evident from differential scanning calorimetry (DSC) and Raman analyses, which show distinct characteristic temperatures (Tg, Tx, and Tp) and bonding type with increasing Ag content (decreasing As content). Specifically, at high Ag content beyond 38 at.% (As below 20 at.%), two additional exothermic peaks appear in DSC curves, and a strong As–Se bonding peak appears in Raman. The structural change is closely related to the variation of glass conductivity in a complex way, which first decreases with increasing Ag content, from 1.14 × 10−6 S cm−1 at 32 at.% Ag to 2.88 × 10−7 S cm−1 at 36 at.% Ag, but then with further increase in Ag, conductivity increases rapidly and reaches the maximum of 5.20 × 10−6 S cm−1 at the maximum Ag content 40 at.%. The abnormal change in conductivity is interpreted as due to the mutual effects of Ag doping as well as the degree of deviation from stoichiometry of the glass forming units. The impedance spectra identify little ionic contribution to the total conductivity which is supported from Raman spectra of the glasses and XRD analyses of the samples after thermal crystallization, both showing evidences of the presence of lone pair electrons of the chalcogen atoms. This work highlights the importance of compositional adjustment for the modification of physical properties in chalcogenide glasses, and provides a scientific basis for potential applications of such glasses in electronic devices.