An estimate of the pressure dependence of the dielectric constant in alkali halides

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Abstract
The determination of the pressure dependence of the static dielectric constant, ϵS, from the Szigeti relations, demands the knowledge of the volume dependence of the Szigeti charge e*, which unfortunately is unknown. By using the classical Lorentz‐Lorenz relation and connecting the ionic polarizability to the bulk modulus a simple relation for dϵS/dP is derived; although it gives the correct order of magnitude, the calculated values exceed the experimental ones by a factor 1.2 to 2. This difference is possibly due to the increase of e* with pressure. A simple relation for the Gruneisen constant of the transverse optical mode is also given.