Elements of Thermodynamics of Dielectrics and Basic Theory of Fröhlich Entropy

This chapter provides the basic elements of thermodynamics of linear dielectrics. It begins by examining the fundamental thermodynamic relationships of dielectric materials under static electric fields, including definitions of thermodynamic potentials like energy, entropy, Helmholtz free energy, and how these quantities depend on the applied field. The categorization of macroscopic temperature-dependent effects and quantities related to dielectric behavior are discussed. Starting from ideal, loss-free dielectrics in equilibrium, the chapter outlines the formal construction of the thermodynamic potentials within H. Fröhlich’s theory. It then addresses key applications such as phase transitions in ferroelectrics, polar liquids, and nematogenic systems. Finally, the thermodynamic response of non-ideal dielectrics is described in broad terms from a phenomenological perspective, highlighting the role of relaxation processes and energy dissipation in real materials.