Crystallization of Glass: What We Know, What We Need to Know

Abstract

The relevance of the concepts of fragility and of the glass transition temperature for the understanding of crystal nucleation and growth in glass-forming liquids is explored. It is shown that classical fragility can be relevant for the understanding of the crystallization behavior only if several severe conditions are fulfilled that are rarely met. By this reason, a new definition of liquid fragility is introduced shown to be able to reflect appropriately the maxima of crystal nucleation, growth, and overall crystallization rates. The origin of the previously reported correlations between glass transition temperatures and intensity of crystallization processes is specified. Further, interpreted in terms of classical nucleation theory, for a variety of oxide glassforming liquids, the thermodynamic barrier for homogeneous crystal nucleation exhibits at high undercooling an unusual increase with a decrease in temperature. Such behavior cannot be explained in terms of classical nucleation theory. Different directions of generalization of the classical theory are discussed, which may lead to a resolution of these problems. The realization of such generalization is considered to be a prerequisite for a generally deeper understanding of the complex phenomena occurring in melt crystallization with its rich field of applications.

Curvature dependence of the surface tension and crystal nucleation in liquids

“…As it turns out the mentioned assumptions lead to severe problems in the theoretical description reviewed in detail in . For this reason, an alternative approach has been advanced by us based on a generalization of Gibbs’ classical treatment going beyond these simple approximations . It accounts appropriately for possible differences of both bulk and surface properties of critical clusters as compared to the respective macroscopic phases.…”

“…In such approach a good agreement can be reached between theory and experiment from the melting or liquidus temperature down to temperatures near to the maximum of the steady state nucleation rate. For lower temperatures, additional factors have to be accounted for in the theoretical description of crystal nucleation employing assumptions going beyond CNT (for details see and also recent molecular dynamics simulations). Latter problems are not considered here.…”

Thermodynamic Aspects of Pressure‐Induced Crystallization: Kauzmann Pressure

“…For the systems studied, for example, in Ref. and exhibiting such minimum, the range of active nucleation is found at temperatures far above the Kauzmann temperature. From an experimental point of view, this statement is confirmed by computations of the Kauzmann temperature from specific entropy data of liquid and crystal and its comparison with experimental measurements of homogeneous nucleation rates and their interpretation .…”

“…The location of these maxima and the value of the thermodynamic driving force at these maxima we will estimate here generalizing first attempts in this direction as outlined in Ref. .…”

“…With the assumption , we get the simple approximation we proposed in Ref. to denote as Tammann–Meissner–Rie equation. For typical glass forming melts, the ratio varies in the range .…”