Pressure dependence of the refractive index and dielectric constant in a fluoroperovskite, KMgF3

Abstract

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 $\ensuremath{\lambda}=589.3$ nm increases monotonously in proportion to pressure $p$ with a slope of $\frac{\ensuremath{\partial}n}{\ensuremath{\partial}p}=2.46\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}{\mathrm{kbar}}^{\ensuremath{-}1}$. 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 ${\mathrm{m}}^{4}$ ${\mathrm{C}}^{\ensuremath{-}2}$. These data are compared with the $\frac{\ensuremath{\partial}n}{\ensuremath{\partial}p}$ values and the ${Q}_{h}$ coefficients of various alkali fluorides and perovskite oxides.