Thermodynamics

Abstract

Thermodynamics plays a special role in solid-state chemistry because of the importance of heterogeneous equilibria in the synthesis of many solids of physical and chemical interest. The understanding of such equilibria is made especially important by the occurrence of nonstoichiometry in solids. The nonstoichiometry of solids ranges from very narrow (“line compounds” with negligible ranges of chemical content but usually with important effects on properties such as conductivity) to wide, e.g., 10% or more variation in Y/M. Both cases are considered in this chapter. The understanding of the heterogeneous behavior of systems can be based upon phase diagrams or upon the mathematical relationships of thermodynamics, and is greatly assisted by insight into the interrelationship between these two aspects of the expression of thermodynamic laws. This chapter has as its purpose the development of the general, basic features of these laws as they apply to heterogeneous equilibria.