Part IV presents advanced techniques and methods that are useful for understanding phase transitions in materials. The emphasis is on aspects of free energy, energy, entropy, and kinetic processes, and less on specific phase transformations. The chapters are far from a complete set of advanced topics, however, and other topics can be argued to be just as important. The topics in Part IV have proved their value, though, and appear in the literature with some frequency. The reader is warned that some of the presentations assume a higher level of mathematics or physics than the other sections in the book, and some important results are stated without proof.

The chapters in Part IV follow no natural sequence, and may be selected for interest or need. Some topics on energy (Chapter 21), entropy (Chapter 24), and atom movements (Chapter 23) are continuations of content in Chapters 6, 7, 9 of Part II. Chapter 19 presents analyses of phase boundaries at low and high temperatures, and Chapter 20 presents techniques for analyzing thermodynamics and physical properties very close to a critical temperature.