10 - Models for Predicting Phase Stability and Structure

Summary

Introduction

We began Chapter 1 by noting that the central, fundamental question that motivates continued materials research is, how can elements be combined to produce a solid with specified properties? Previously, we divided this problem into three separate issues that we restate here to provide appropriate context for the final chapter. First, when any given elements are combined under some controlled conditions, will they react to form a compound, will they dissolve in one another, or will they be immiscible? Second, what structure will the product of this combination have and how will it be influenced by the conditions under which the elements were combined? Third, given the product phase or phases and the structure, what are the properties of this material? In this chapter, we will discuss approaches that have been developed to predict answers to at least parts of the first two questions. For the purposes of this course, we limit our structural discussion to the atomic structure. However, we note that to fully answer these two questions, the defect structure and microstructure must also be addressed.

It was noted earlier that the quantitative physical models for bonding described in Chapters 6–9 were not able to reliably predict the equilibrium crystal structure of a compound. Despite impressive theoretical achievements and the development of more advanced models during the past few decades, phase stability, crystal structures, and the properties of solids must still be determined experimentally.