POLAR PROPERTIES OF A MESOSCOPIC FERROELECTRIC

At the 1995 Williamsburg workshop we reported([3]) on the condensation of polar nanoregions in KTa1-xNbxO3 approximately 20 K above the actu al ferroelectric transition for Nb concentrations ranging from 1.2% to 30%. We have now studied the novel polar properties to which these na noregions give rise. These include slow relaxational dynamics manifest ed by a strong dispersion in the low frequency dielectric response, de viations from a Curie-Weiss-like behavior and the appearance of higher harmonics in the polarization response signaling the onset of non-lin earities. The first non-linear coefficient of the susceptibility has b een derived from dielectric measurements in the presence of de bias fi elds. The measurements under external fields also reveal the appearanc e of piezoelectric resonances that are temperature dependent. These pr operties may be characteristic of other ferroelectric systems with pol arization inhomogeneities on a mesoscopic scare.