Effect of Pressure on the Low Frequency Dielectric Constant of Ionic Crystals

Data on the pressure dependence of the dielectric constant $\epsilon$ of MgO, LiF, NaCl, KCl and KBr at 1000 c.p.s. and room temperature are given as a function of hydrostatic pressure from 0 to 8000 bars. The dielectric constants are found to decrease with an initial slope ${\left(\frac{\partial \ln \epsilon }{\partial p}\right)}_T$ ranging from -0.32×${10}^{-5\mathrm{}}$ ${\mathrm{bar}}^{-1\mathrm{}}$ in the case of MgO to -1.17×${10}^{-5\mathrm{}}$ ${\mathrm{bar}}^{-1\mathrm{}}$ in the case of KBr. Present lattice theories are only capable of explaining these data if the inner field decreases with increasing pressure.