A composition dependent thermal behavior of GexSe35−xTe65 glasses

Alternating differential scanning calorimetric (ADSC) studies have been performed to understand the thermal behavior of bulk GexSe35−xTe65 glasses (17 ⩽ x ⩽ 25); it is found that the glasses with x ⩽ 20 exhibit two crystallization exotherms (Tc1 & Tc2). On the other hand, those with x ⩾ 20.5, show a single crystallization reaction upon heating. The exothermic reaction at Tc1 has been found to correspond to the partial crystallization of the glass into hexagonal Te and the reaction at Tc2 is associated with the additional crystallization of rhombohedral GeTe phase. The glass transition temperature of GexSe35−xTe65 glasses is found to show a linear but not-steep increase, indicating a progressive, but a gradual increase in network connectivity with Ge addition. It is also found that Tc1 of GexSe35−xTe65 glasses with x ⩽ 20, increases progressively with Ge content and eventually merges with Tc2 at x ≈ 20.5 (〈r〉 = 2.41); this behavior has been understood on the basis of the reduction in TeTe bonds of lower energy and increase in GeTe bonds of higher energy, with increasing Ge content. Apart from the interesting composition dependent crystallization, an anomalous melting behavior is also exhibited by the GexSe35−xTe65 glasses.