FIELD-INDUCED PIEZOELECTRIC RESONANCES IN THE SUPERPARAELECTRIC PHASEOF KTN

A new type of dielectric resonances has been observed in mixed ferroel ectric, KTa1-xNbxO3 (KTN), also known to belong to the family of Relax er Ferroelectrics. These resonances and their metastability in KTN pro vide clear evidence for the presence of permanent polar nanoregions wi th a local spontaneous polarization and a local strain field. The appl ication of a small dc bias field can align these regions and activate a strong polarization-strain coupling that give rise to the observed d ielectric/mechanical resonances. These resonances are found to persist over long periods of time, indicating that the field-induced macrosco pic polarization is stabilized by this coupling. Their frequencies can be calculated from the elastic constant, which reveals the unexpected clamped nature of the resonance. These results constitute an importan t piece of evidence in support of the role of polar regions in explain ing the Relaxer behavior.