Standard thermodynamic functions of GeS :Bi (1 < x < 2) glasses

The heat capacity of four samples of high-purity chalcogenide glasses GeS _x: nBi ( х = 1.25, 1.35, 1.4, 1.6; n = 1 at. %) in the region of 300–750 K was measured by the differential scanning calorimetry (DSC) method. According to the data obtained, standard thermodynamic functions (STF) were calculated with regard for the established characteristics of the glass transition: heat capacity С _p ^°( Т), enthalpy H ^°( T) − H _l ^°(0), entropy S ^°( T) − S _l ^° (0) and Gibbs energy G ^°( T) − H _l ^° (0) in the region T → 0 to 750 K in the glassy and «supercooled liquid» states. For these glasses, the glass transition temperatures ( T _g ) ranged from 620 to 655 K increasing with increasing S content. The linear expansion coefficients were measured at room temperature and the average value was (15 ± 0.225)·10 ⁻⁶ К ⁻¹ . The use of parametric similarity of properties in the framework of the model-statistical approach makes it possible to predict the STF for unexplored glasses of this series. The standard enthalpies of glass formation for each composition were calculated using the valence-state (VSM) model, and the valence-orbital characteristics of Ge, S, and Bi atoms were calculated which made it possible to determine the dependence of the charge distribution on these atoms on the sulfur content of the glass composition.