Viscosity and Glass Transition in Amorphous Oxides

Abstract

An overview is given of amorphous oxide materials viscosity and glass-liquid transition phenomena. The viscosity is a continuous function of temperature, whereas the glass-liquid transition is accompanied by explicit discontinuities in the derivative parameters such as the specific heat or thermal expansion coefficient. A compendium of viscosity models is given including recent data on viscous flow model based on network defects in which thermodynamic parameters of configurons—elementary excitations resulting from broken bonds—are found from viscosity-temperature relationships. Glass-liquid transition phenomena are described including the configuron model of glass transition which shows a reduction of Hausdorff dimension of bonds at glass-liquid transition.

Observing the twinkling fractal nature of the glass transition

“…The observation of fractal structure in amorphous polystyrene is in accord with observations of the fractal structure in amorphous metals, where D f = 2.31 was reported from neutron and X-ray scattering experiments below T g [31]. Recently, Ojovan examined solid-liquid bond transitions in SiO 2 and GeO 2 oxides and reported percolation behavior of the solid regions with fractal dimensions D f =2.55 [32][33][34]. …”

Viscosity of many-component glasses

“…Arguments that the value of A is virtually composition-independent have been summarized in various papers, most recently by Ojovan [15]. Since A = constant, the viscosity can be normalized as g/g 1 where g 1 = e A is the asymptotic viscosity, and the activation energy can be expressed as…”

Interrelation between the parameters of equations of viscous flow and chemical composition of glassforming melts

“…(1) cannot describe quantitatively the temperature dependence of viscosity. Therefore, the contemporary viscosity models (see for instance the reviews of Ojovan [2,3]) assume that the activation energy ΔE = ΔE(T) depends on temperature. Because of the disorder, the building units of glassforming systems inevitably meet energy barriers of different heights.…”