For some chalcogenide glasses, the temperature dependence of the activation energy E(T) of viscous flow in the glass transition region was calculated using the Williams–Landel–Ferry (WLF) equation. A method for determining the activation energy of viscous flow as a function of temperature is proposed using the Taylor expansion of the function E(T) using the example of chalcogenide glasses As-Se, Ge-Se, Sb-Ge-Se, P-Se, and AsSe-TlSe. The calculation results showed that the temperature dependence of the activation energy for the Ge-Se, As-Se, P-Se, AsSe-TlSe, and AsSe systems is satisfactorily described by a polynomial of the second degree, and for Sb-Ge-Se glass by a polynomial of the third degree. The purpose of this work is to compare the values of the coefficients obtained from the Taylor series expansion of E(T) with the characteristics of the E(T) versus (T − T_g) curves obtained directly from the experimental temperature dependence of viscosity. The nature of the dependence E(T) is briefly discussed.

We present calculation results of the temperature interval δT_g characterizing the liquid–glass transition in amorphous materials obtained on the basis of available data of the empirical parameters C₁ and C₂ in the Williams–Landel–Ferry (WLF) viscosity equation. We consider the unambiguous dependence of the relative transition temperature interval δT_g/T_g on the fraction of the fluctuation volume f_g frozen at the glass transition temperature T_g utilizing Sanditov’s model of delocalized atoms. The parameter f = ΔV_e/V, which determines the molecular mobility characteristic of delocalized atoms in the liquid–glass transition region, is weakly dependent on the nature of most vitreous substances and can be found as f_g = 1/C₁. We show that the temperature interval δT_g is less than 1% of the T_g for most amorphous substances. This result conforms with Simon’s classical idea of a small temperature range in which the structure freezes. The structural relaxation time τ_g at T_g of polymers and chalcogenide glasses is also calculated.

This paper is concerned with the temperature dependence of viscosity for sodium germanate glasses differing in sodium oxide content and discusses some aspects of the liquid–glass transition in them, including a kinetic glass transition criterion. Using parameters of the Williams–Landel–Ferry (WLF) equation, we have calculated the temperature range characterizing the glass transition region and the structure relaxation time at the glass transition temperature of the glassed studied. We propose generalization and substantiation of the Schmelzer kinetic glass transition criterion.

The temperature dependence of the viscosity of inorganic glasses in the glass transition region is successfully described by the Williams--Landel--Ferry (WLF) equation. For the studied glasses, the value of f_g=1/C₁ weakly depends on the nature of the glasses. There is a linear correlation between delta delta T_g and T_g. From the data on the parameters of the WLF equation C₁ and C₂, we calculated delta delta T_g, as well as the relaxation time of the structure tau_g at the glass transition temperature of the glasses under study. Keywords: Viscosity in the glass transition region, Williams--Landel--Ferry equation, kinetic glass transition criterion, chalcogenide glasses, fluctuation volume fraction, liquid--glass transition.

It is shown that the empirical Williams–Landel–Ferry (WLF) and Vogel–Fulcher–Tammann (VFT) equations, as well as the semiempirical equations of other researchers, for the viscosity η in the glass transition region are, in fact, hyperbolic functions of temperature with corresponding relationships between their parameters. The hyperbolic dependence can be derived from the mathematically common expansion of lnη into a Taylor series in a small temperature parameter near the glass transition temperature, provided that the temperature range satisfies approximately (T − T_g)/T_g ≲ 0.1–0.15). The applicability of the principle of corresponding states for glasses of similar composition follows from this expansion. A new two-parameter equation in the form of a second-degree polynomial is proposed for ln(η) in the glass transition region. This equation contains physically significant parameters and adequately describes the available experimental data for individual glass-forming substances. The temperature range over which the proposed series expansion up to the third (quadratic in the small parameter) term is valid can be determined only experimentally, because the coefficients of the series depend on the nature of the glass. For the specific experimental data we used, the sharp temperature dependence of the viscosity in the glass transition region makes the quadratic polynomial applicable over almost the entire temperature range studied.