Parameters of the Fluctuation Free Volume Theory for Glasses in the Ge–As–Se System

Author： Mel'nichenko T. D. Rizak V. M. Mel'nichenko T. N. Fedelesh V. I.

ISSN： 1087-6596

Source： Glass Physics and Chemistry, Vol.30, Iss.5, 2004-09, pp. : 406-414

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Abstract

The fraction of fluctuation free volume (f_g = V_f/V) frozen at the glass transition temperature T_g is determined from the temperature dependence of the viscosity in the glass transition range in terms of the Vogel–Fulcher–Tammann equation and the formula α_fT_g ≅ ∆αT_g = f_gln(1/f_g). The fluctuation free volume fractions f_g obtained according to these two procedures for glasses in the Ge–As–Se system are in quite reasonable agreement. The energies E_h of formation of fluctuation microvoids and their volumes V_h are calculated. It is demonstrated that the quantities f_g, E_h, and V_h and the ratio of the microhardness H to T_g depend substantially on the glass structure and can serve as characteristics of the rigidity of the glass networks. It is noted that the fluctuation free volume fraction f_g is a nonmonotonic function of the mean coordination number Z_m and that it exhibits a specific dependence on the lattice Grüneisen parameter γ. The Poisson ratios μ are estimated from the fluctuation free volume fraction f_g with the use of the relationship f_gln(1/f_g) = $\frac{(1 - 2\mu)^{2}}{2(1 + \mu)}$ . It is shown that the Poisson ratios μ thus obtained are close to those calculated from the data on the transverse (V_s) and longitudinal (V_l) velocities of ultrasound.