Compositional dependence of thermal stability, glass-forming ability and fragility index in some Se-Te-Sn glasses

摘要

Non-isothermal DSC thermograms were obtained for the ternary Se_(90)Te_(10-x)Sn_x (x = 2,4,6 and 8) chalcogenide glasses in order to determine the melting temperature T_m, glass transition temperature T_g, onset T_c and peak T_p temperatures of crystallization. These temperatures were utilized to investigate the thermal stability through the calculations of temperature difference (T_c-T_g), the glass transition activation energy E_t, the parameter S and the average value of crystallization rate factor (K_p). In addition, the glass forming ability was estimated by the criteria of reduced glass transition temperature, T_(rg) and Hruby parameter H_R. The fragility index m for the present glasses was determined in order to see whether these materials are obtained from strong or fragile glass-forming liquid. Results reveal that, both thermal stability and glass forming ability exhibit a maximum at x = 4at.% of Sn. Meanwhile, the prepared glasses were obtained from strong glass-forming liquid as evident from the fragility index calculations. The compositional dependence of the above parameters was discussed on the basis of Philips and Thorpe topological model and the critical composition occurs at an average coordination number (r) = 2.16 but not 2.40. This is due to the formation of iono-covallent bonds when the glass doped with heavy elements like Sn.