Dielectric relaxation and resonance in relaxor ferroelectric K12xLixTaO3

Polar regions are shown to mediate a strong coupling between polarization and strain in the paraelectric phase of the mixed ferroelectric K12xLixTaO3 ~KLT! and KTa12xNbxO3 resulting in a field-induced piezoelectric response. The coupling is shown to result in a resonance in the dielectric spectrum of the crystals. In KLT, polar nanoregions can reorient via 180° ~p relaxation! or 90° ~p/2 relaxation! rotations. While the p relaxation is of no consequence, the p/2 relaxation has a strong influence on the overall character of the resonance. In addition to providing a mechanism for loss and degradation of the quality factor, this relaxation alters the character of the resonance as the two cross. Experimental results from dielectric spectroscopy above and below this crossover are presented and discussed. A simple theoretical Debye model involving the electrostrictive polarization-strain coupling is presented and the calculated spectrum is shown to reproduce the experimental spectrum. The parameters derived from the model are discussed. Most significantly, the electrostrictive coefficient of KLT is found to be 100 times larger than that of BaTiO3, and is due to the presence of polar nanoregions. @S0163-1829~99!13833-5#