Mechanisms that determine the electronic dielectric constants of ionic crystals

The very old and widely accepted theory for the electronic dielectric constants of ionic crystals assumes that intra-ionic excitations dominate in the crystal whereby polarizabilities of individual ions may be identified and tabulated. It is shown here that this assumption is unfounded and leads to inconsistencies and unphysical results. In turn I present theoretical and experimental evidence that the mechanism determining the dielectric constants is in fact the extreme opposite, namely strictly interionic excitations, whereby the concept of polarizability of ions in solids is physically meaningless. © 1975 The American Physical Society.