A composition dependent thermal behavior of Ge Se35−Te65 glasses

Abstract Alternating differential scanning calorimetric (ADSC) studies have been performed to understand the thermal behavior of bulk Ge x Se 35− x Te 65 glasses (17 ⩽ x ⩽ 25); it is found that the glasses with x ⩽ 20 exhibit two crystallization exotherms ( T c1 & T c2 ). On the other hand, those with x ⩾ 20.5, show a single crystallization reaction upon heating. The exothermic reaction at T c1 has been found to correspond to the partial crystallization of the glass into hexagonal Te and the reaction at T c2 is associated with the additional crystallization of rhombohedral Ge Te phase. The glass transition temperature of Ge x Se 35− x Te 65 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 T c1 of Ge x Se 35− x Te 65 glasses with x ⩽ 20, increases progressively with Ge content and eventually merges with T c2 at x ≈ 20.5 (〈 r 〉 = 2.41); this behavior has been understood on the basis of the reduction in Te Te bonds of lower energy and increase in Ge Te bonds of higher energy, with increasing Ge content. Apart from the interesting composition dependent crystallization, an anomalous melting behavior is also exhibited by the Ge x Se 35− x Te 65 glasses.