ABSTRACT
This chapter evolves out of many years of research in materials for thermoelectrics. The study of phase diagrams is necessary to understand the synthesis of established thermoelectric materials, enhance the material properties, and contribute to the development of new and better materials. Thermodynamics is a powerful science for studying the materials. The principles of thermodynamics of heterogeneous equilibria were developed by J. W. Gibbs. He fixed the rules applicable to the phase relationships in a system. The well-known phase rule of J. W. Gibbs is the core of this part of thermodynamics. It stands that the maximum number of phases stable simultaneously is determined by the number of independent variables of state according to the equation V=c+2−f. The thermodynamic modeling of the solid phases of a system must be done in two ways. In the absence of any crystallographic information, the modeling can be assumed as a classical Redlich–Kister equation.
