Section 1.1 put phase transitions in materials into a broader context of phase transitions in general. Most of this book has been on how atoms arrange themselves at different T and P, and how these arrangements change abruptly through a phase transition. Atoms in solids tend to be a bit sluggish in their movements, however, and their arrangements can be slow to attain states of thermodynamic equilibrium. Diffusion and nucleation, which retard, redirect, or even arrest the paths to equilibrium, are kinetic phenomena of interest and importance. Those nonthermodynamic phenomena are essential to the full life cycle of a phase transformation, but they obscure the singularities in the free energy function or its derivatives that underlie the thermodynamics of a phase transition.

The more general field of phase transitions often places rigorous emphasis on thermodynamic equilibrium, even at temperatures that are very low, or at temperatures very near a critical temperature where atomic structures may not attain equilibrium in reasonable times. Liquid–gas transitions and magnetic transitions are often better candidates for studies of phase transitions for their own sake. Nevertheless, concepts from the broader field of phase transitions do help our understanding of phase transformations in solid materials. Much of the interest in the basic physics of phase transitions is in how a system behaves very close to the critical temperature.