PRESSURE AND TEMPERATURE-DEPENDENCE OF THE SINGLE-CRYSTAL ELASTIC-MODULI OF THE CUBIC PEROVSKITE KMGF3

The elastic moduli (c) of single crystal KMgF3 have been determined by the ultrasonic pulse superposition technique as a function of temperature from T=298-550 K, and as a function of pressure from P=1 bar-2.5 kbar. Room temperature values of the elastic moduli and their temperature derivatives are consistent with Reshchikova's (1969) values. Comparison with the data for SrTiO3 indicates that, for most of the moduli, 1/c(∂c/∂T)P and (∂c/∂P)T are very similar for the fluoride-oxide analogue pair, KMgF3-SrTiO3. Values of (∂c/∂P)T for KMgF3 are calculated from a simple central force model using parameters determined for KF and are in good agreement with the measured values. The bulk sound velocity-mean atomic weight relationship, vf{cyrillic}M1/2=constant, is well obeyed by the fluoroperovskites; comparison with the perovskite oxide data on a log-log plot of vf{cyrillic} versus M leads to a value of 70% for the relative effective charge of the oxides with respect to the fluorides. © 1979 Springer-Verlag.