Static dielectric constant of KNbO3 under quasi-hydrostatic pressure

The effect of pressure on the static dielectric constant (kappa) of single crystals of KNbO3 is investigated by means of capacitance measurements. The dielectric constant increases with pressure up to 22.5 kbar, where it exhi bits a large value (kappa=5000), and then decreases. This change in its beh avior is related to a phase transition induced by pressure. It is suggested that below 22.5 kbar, the pressure dependence of kappa obeys a Curie-Weiss -type law. As the large value of kappa is connected to a transverse optic s oft mode, we have associated a displacive character to the induced phase tr ansition. On decompression, the samples do not revert back to the ambient p ressure phase.