Thermodynamic and tensorial aspects of phenomenological response of crystals to electric fields

Abstract

From the point of view of thermodynamics and group theory it is shown that the classical approach to non linear phenomena as second harmonic generation and electrooptic effects is valid but not complete. For instance the permittivity at high frequency cannot be described by a symmetric matrix; an antisymmetric part must be added which modifies the structure of the plane propagating wave. Results of discussion are given for some point groups of interest for ferroelectrics.