The hydrostatic-pressure dependence of the refractive index and the low-frequency dielectric constant of a perovskite-type single crystal, KMg${\mathrm{F}}_3$, have been determined at room temperature. The refractive index $n$ for $\lambda =589.3\mathrm{}$ nm increases monotonously in proportion to pressure $p$ with a slope of $\frac{\partial n}{\partial p}=2.46\mathrm{}\times {10}^{-4\mathrm{}}{\mathrm{kbar}}^{-1\mathrm{}}$. On the other hand, the dielectric constant at 10 kHz decreases with increasing pressure, from which the electric-displacement-related electrostrictive coefficient $Q_h$ ($=Q_{11}+{2Q}_{12}$) is calculated as 0.24 ${\mathrm{m}}^4$ ${\mathrm{C}}^{-2\mathrm{}}$. These data are compared with the $\frac{\partial n}{\partial p}$ values and the $Q_h$ coefficients of various alkali fluorides and perovskite oxides.

• Received 30 June 1983

DOI:https://doi.org/10.1103/PhysRevB.29.6921