Elasticity and its limits: Yielding and melting in (modulated) ionic crystals

A microscopic foundation of the theory of static isothermal homogeneous deformation is given for classical (ionic) crystals which may have atomic electric dipoles and which may be in a structurally modulated (slightly distorted) phase. Special effects due to the dipoles and the modulations are mentioned and a comparison is made with the dynamic elasticity as measured via acoustic waves. An attempt is made to predict the limits of the elastic regime i.e. yielding under stresses and melting under heating.