Topological Constraint Theory of Inorganic Glasses

Originally, the topological constraint theory (TCT) represented simple theoretical inquiries about the existence of Zachariasen's topologically disordered networks and easy glass formation. Over the last 25 years it has evolved to a widely used formalism for modeling composition–property relationships in glasses and glass-forming liquids. Although somewhat approximate and lacking fundamental basis, TCT yields results that are in good agreement with observations. This is largely because it takes as input experimentally (or model-based) information on the variation of structure with composition and a theoretically sound temperature dependence of chemical-bond strengths. In this chapter, we review the basic concepts and the recent extension of TCT to temperature-dependent bond constraints. In addition, some of the fundamental issues that remain unresolved are highlighted.