Linear Dielectric Thermodynamics: A New Universal Law for Optical, Dielectric Constants

TL;DR

This paper develops a thermodynamic framework for linear dielectrics, proposing a universal law linking dielectric constants to specific volume, and highlights the stability of isentropic dielectric behavior across temperatures and pressures.

Contribution

It introduces a new universal law relating dielectric constants to specific volume, based on thermodynamic principles, applicable to all optical materials.

Findings

Dielectric constant is proportional to the square root of specific volume.

Isentropic dielectric constants are always positive and stable.

Electronic entropy contributions can be negative, indicating instability at high temperatures.

Abstract

Linear dielectric thermodynamics are formally developed to explore the isothermal and adiabatic temperature - pressure dependence of dielectric constants. The refractive index of optical materials is widely measured in the literature: it is both temperature and pressure dependent. The argument to establish the dielectric constant's isentropic temperature dependence is a thermodynamic one and is thus applicable to all physical models that describe electron clouds and electronic resonances within materials. The isentropic slope of the displacement field versus the electric field at all temperatures is described by an adiabatic dielectric constant in an energy-per-unit mass system. This slope is shown through the electronic part of the entropy to be unstable at high temperatures due to the change in the curvature of the temperature dependence of the dielectric constant. The electronic entropy contribution for optical, thermo-electro materials has negative heat capacities which are unacceptable. The dielectric constant's temperature and pressure dependence is predicted to be only dependent on the specific volume so isentropes are always positive. A new universal form for the dielectric constant follows from this hypothesis: the dielectric constant is proportional to the square root of the specific volume.