On the glass transition temperature and related parameters in the glassy GexSe1-x system

High-purity GexSe1-x amorphous samples of different composition (0.05 less than or equal to x less than or equal to 0.30) were prepared. An empirical relation between the glass transition temperature (T-g) and the coordination number N-o is proposed by modifying the Gibbs-Di Marzio equation for glass transition temperature of a cross-linked polymer as a function of cross-linked density. The utility of the Gibbs-Di Marzio relation was achieved by estimating T-g theoretically. The T-g results were also compared with an arbitrary defined optical gap (E-o) where T-g provided an index of atomic mobility, and E-o an index of covalent bond strength. From the previous calculations the T-g-E-o correlation is interpreted in terms of a proposed fluidity equation for covalent liquids with 2.1 less than or equal to N-c less than or equal to 2.7. The relationship between E-o and the chemical composition in the vacuum prepared GexSe1-x is discussed in terms of the average heat of atomization (H-s) and the average coordination number (N-c). The effect of both the chemical composition and the nature of the chemical bonding on the efficiency of the structural modification (Delta Phi) of the GexSe1-x system is also analyzed. (C) 2001 Elsevier Science B.V. All rights reserved.