Glass transition kinetics and fragility index of chalcogenides from Ag–As–S–Se system

• Published in: Journal of thermal analysis and calorimetry 2018-10, Vol.134 (1), p.297-306
• Main Authors: Strbac, Goran R, Petrovic, Jelena S, Strbac, Dragana D, Cajko, Kristina, Lukic-Petrovic, Svetlana R
• Format: Article
• Language: English
• Subjects: Activation energy; Analysis; Analytical Chemistry; Calorimetry; Chalcogenides; Chemistry; Chemistry and Materials Science; Composition; Fragility; Glass transition temperature; Heating rate; Inorganic Chemistry; Mathematical models; Measurement Science and Instrumentation; Parameters; Physical Chemistry; Polymer Sciences; Silver; Temperature; Temperature dependence
• ISSN: 1388-6150; 1588-2926
• DOI: 10.1007/s10973-018-7151-9

The glass transition temperature dependence on a heating rate was investigated by differential scanning calorimetry for chalcogenide glasses from the Ag x (As 2 (S 0.5 Se 0.5 ) 3 ) 100− x system for x  = 0, 0.5, 2 and 3 at.%. According to this dependence, apparent glass transition activation energies E g were calculated for differently defined glass transition temperatures (onset T g1 , midpoint T g2 , endpoint T g3 and endset T g4 ). Also, E g was analysed using isoconversional (model free) method. The results showed that the activation energy is not constant during the investigated process and vary with the extent of transformation from the glassy to the supercooled phase, pointing out that a complicated, multi-step process occurs. E g decreases from about 340 to 200 kJ mol −1 in the composition with 2 at.% of silver. The values of the fragility index showed that these glasses do not exhibit large configuration changes during the glass transition process. Influence of silver content on investigated parameters was discussed. Apparent glass transition activation energy, variability parameter and fragility index showed a significant change in their values for the composition with 3 at.% of silver. Application of the isoconversion model for determination of apparent glass transition activation energy has showed that this parameter (at extent of conversion of 0.5) decreases from about 260 kJ mol −1 for x  = 0, 0.5, 2 at.% to about 185 kJ mol −1 for x  = 3 at.% of silver content. Likewise, fragility parameter drops from ~ 28.5 for x  = 0, 0.5, 2 at.% to 21.5 x  = 3 at.% of silver.