Liquid-liquid transition and polyamorphism

Abstract

Two or more liquid states may exist even for single-component substances, which is known as liquid polymorphism, and the transition between them is called liquid-liquid transition (LLT). On the other hand, the existence of two or more amorphous states is called polyamorphism, and the transition between them is called amorphous-amorphous transition (AAT). Recently, we have accumulated a lot of experimental and numerical evidence for LLT and AAT. These intriguing phenomena provide crucial information on the fundamental nature of liquid and amorphous states. Here, we review the recent progress in this field and discuss how we can physically rationalize the existence of two or more liquids (glasses) for a single-component substance. We also discuss the relationship between liquid-, amorphous-, and crystal-polymorphisms, putting a particular focus on the roles of thermodynamics, mechanics, and kinetics.