Pressure Dependence of the Dielectric Constant of Strontium Titanate

The effect of pressure, up to 50 kbar, on the low-frequency dielectric constant $\epsilon$ of SrTi${\mathrm{O}}_3$ has been measured at 25°C. $\epsilon$ decreases with increasing pressure according to the relation $\epsilon =\frac{C^{*}}{(p-p_0)}$ with $C^{*}=12600\mathrm{}$ kbar and $p_0=-40\mathrm{}$ kbar. From the present data and the known values of the compressibility and the initial change of the refractive index with pressure, it is shown that the variation of the infrared polarizability with pressure is the predominant factor in determining the change of $\epsilon$. This result is discussed in terms of Cochran's theory which associates the large value of $\epsilon$ with a low-frequency transverse optic mode of vibration.