Effect of Poling Field on Piezoelectric Properties of KNbO3 Crystal Grown by Vertical Bridgman Method

Abstract

Single crystals of KNbO3 were grown by the vertical Bridgman method. The crystals were cut into 6×3×0.5 mm3 plates, and dielectric constants and resonance characteristics were observed as a function of the electric field strength used in the poling treatment. For the [001]pc-poled crystal, which stands for [001] direction in pseudocubic crystal lattice, the dielectric constant increased once with increasing amount of poling field and then decreased again with higher fields. For [101]pc-poled crystal, both a reduction in dielectric constant and a higher phase angle shift in the resonant region were observed when the electric field exceeded 85 V/mm. The series of observations can be consistently interpreted using the domain structures estimated from the anisotropic dielectric constant. The vibrators having their longitudinal directions along the apc and bpc axes showed quite different piezoelectric responses, revealing that the polarization vector lies only in the [101]pc and [101]pc directions.