Behavior of Ferroelectric KNbO3in the Vicinity of the Cubic-Tetragonal Transition

Abstract

The results of measurements on single crystals of KNb${\mathrm{O}}_3$ are reported. From the dielectric constant and spontaneous polarization measurements the coefficients of the first three terms of the free energy expressed as a power series in the polarization can be found. The detailed behavior of single domain crystals in the cubic and tetragonal phases is compared with Devonshire's phenomenological treatment. Agreement with predicted dielectric constant and spontaneous polarization is reasonable. The constants of KNb${\mathrm{O}}_3$ are compared with those reported for BaTi${\mathrm{O}}_3$. It is found that in all cases corresponding constants are of the same order of magnitude.