Amorphous configurational state: energy landscape
Amorphous and glassy states of molecular and pharmaceutical compounds: general properties

The difference in nature between the states of a system, above and below T_g, can be represented schematically on a Gibbs free energy diagram (figure 17). Between T_g and T_m, the system is metastable, but in a state of equilibrium. The situation corresponds to the bottom of the free energy potential well corresponding to the supercooled liquid. Its level is, however, higher than that of the bottom of the well corresponding to the crystal. Below T_g, the system is not even metastable, but unstable. From a free-energy point of view, its position can be schematically described as frozen somewhere on the flank of a potential well. This position depends on the way the glass was formed, and in particular...