A random-field model for polarization reversal in Pb(Yb_(1/2)Nb_(1/2))O_(3)-PbTiO_(3) single crystals

摘要

Polarization switching and dielectric temperature behavior have been investigated in 0.55Pb(Yb_(1/2)Nb_(1/2))O_(3)-0.45PbTiO_(3) (PYN-PT) single crystals. These compositions are of interest owing to their unusually high Curie temperature and high coercive fields. The dielectric permittivity was determined as function of temperature and the polarization was measured as a function of applied field for different drive frequencies. Analysis of the experimental results with a random-field model was found to show similar trends to recent reports for the Pb(Mg_(1/3)Nb_(2/3))O_(3) relaxor materials. The frequency dispersion of the maximum in dielectric spectra, T_(max), was also analyzed with the Vogel-Fulcher relation yielding a high freezing temperature of 577 K. Polarization behavior was found to follow a stretched exponential time dependence and a fractal dimension of ～2.2 was obtained. It is proposed that the polar cluster state in PYN-PT single crystals do not freeze in random orientations but rather arrange locally in preferred configurations. The fraction of the clusters decreases under increasing external field drive, resulting in the formation of the percolated network at higher fields.