Influence of connectivity on the rigidity of the covalently bonded (GeTe4)100−x(As2Se3)x glasses

• Glasses having average coordination number (Zav) = 2.4 have been prepared in GeTe4-As2Se3 tie-line.
• Tg decrease with As2Se3 up to 35 mol.% and saturates in the range 35 ≤ x ≤ 50 and then increases for x ≥ 50.
• The average bond energy of the system increases with the increase of As2Se3 but the density and Tg shows a decreasing trend.
• Raman measurements show that the network is depolymerized with the addition of As2Se3.
• The higher bond energy Ge-Se does not increase indicating connectivity plays a major role than the chemical bonds.

Bulk (GeTe4)100 − x(As2Se3)x(0 ≤ x ≤ 60) glasses in the tie-line GeTe4-As2Se3prepared by melt quenching method are characterized by differential scanning calorimetry (DSC), X-ray diffraction and Raman spectroscopy. In covalent network glasses, the structural network transform from a floppy to a rigid structure at an average coordination number (Zav) 2.40. (GeTe4)100 − x(As2Se3)x glasses in the range 5 ≤ x ≤ 15 exhibit two stage crystallization whereas glasses with x > 15 exhibit single stage crystallization. Annealing of the glasses results into hexagonal GeTe and Te structures for 0 ≤ x ≤ 10 whereas glasses in the range 15 ≤ x ≤ 40 show only Te crystallites. For higher As2Se3 mol. % (x ≥ 50) As2Te3 phase along with Te has been observed. Raman studies indicate the presence of GeSe2, GeTe2, As2Te3, and -Te-Te-structural units. The average coordination number of the glasses prepared in this tie-line is 2.4. Though the overall bond energy of the system increases with the increase of As2Se3, the density (ρ), glass transition (Tg) and specific heat capacity (∆ Cp) show a decreasing trend. The rate of decrease of ρ, Tg and ∆ Cp is slow for 0 ≤ x < 25 and rapid for 25 ≤ x ≤ 40. These results indicate that the rigidity of the structural network decreases with an increase of As2Se3 though the average coordination number remains constant for the entire range of composition.