Glass Transitions. Glassy States and Two Types of Polyamorphism.

Glass transformations, glass transition temperatures, various glassy states under elevated pressures, and polyamorphism are reviewed. There are two types of polyamorphism in the glassy states: the first is that produced from the history of glass-forming conditions, and the second is that produced from changes in the structure of liquids. A critical point of structural polyamorphism is deduced from the recent experiments on the first-order like glass-glass transition of tetrahedral glasses. The critical point locates on the equilibrium liquid surface in the P-V-T space under an elevated pressure below the glass transition temperature, but above the Kauzmann temperature. The low-temperature limit of the liquid under the critical pressure is the critical point; and the liquid, except the critical pressure, vitrifies gradually without any transition. The equations of the glassy states are briefly discussed.