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

The hydrostatic-pressure dependence of the refractive index and the low-frequency dielectric constant of a perovskite-type single crystal, KMgF3, have been determined at room temperature. The refractive index n for =589.3 nm increases monotonously in proportion to pressure p with a slope of np=2.46×10-4kbar-1. On the other hand, the dielectric constant at 10 kHz decreases with increasing pressure, from which the electric-displacement-related electrostrictive coefficient Qh (=Q11+2Q12) is calculated as 0.24 m4 C-2. These data are compared with the np values and the Qh coefficients of various alkali fluorides and perovskite oxides.