Evidence for a thermally reversing window in bulk Ge–Te–Si glasses revealed by alternating differential scanning calorimetry

Abstract

Experiments on Ge₁₅Te_{85− x} Si _x glasses (2 ≤ x ≤ 12) using alternating differential scanning calorimetry (ADSC) indicate that these glasses exhibit one glass transition and two crystallization reactions upon heating. The glass transition temperature has been found to increase almost linearly with silicon content, in the entire composition tie-line. The first crystallization temperature (T _c1) exhibits an increase with silicon content for x < 5; T _c1 remains almost a constant in the composition range 5 < x ≤ 10 and it increases comparatively more sharply with silicon content thereafter. The specific heat change (ΔC _p) is found to decrease with an increase in silicon content, exhibiting a minimum at x = 5 (average coordination number, ⟨r⟩ = 2.4); a continuous increase is seen in ΔC _p with silicon concentration above x = 5. The effects seen in the variation with composition of T _c1 and ΔC _p at x = 5, are the specific signatures of the mean-field stiffness threshold at ⟨r⟩ = 2.4. Furthermore, a broad trough is seen in the enthalpy change (ΔH ^NR), which is indicative of a thermally reversing window in Ge₁₅Te_{85− x} Si _x glasses in the composition range 2 ≤ x ≤ 6 (2.34 ≤ ⟨r⟩ ≤ 2.42).

Acknowledgement

The financial support of Applied Materials Inc, USA, is gratefully acknowledged.