POLAR METASTABILITY AND AN ELECTRIC-FIELD-INDUCED PHASE-TRANSITION INTHE DISORDERED PEROVSKITE PB(MG1 3NB2/3)O3/

We measure the effect of dc-electric-field-temperature sequences on th e finite-frequency dielectric constant epsilon(omega), and the thermal ly stimulated depolarization current of single crystals of Pb (Mg1/3Nb 2/3)O3 (PMN). The results are interpreted in terms of a field-induced change in the low-temperature phase of PMN from glassy to rhombohedral ferroelectric. The latter transition has first-order characteristics, and occurs only if a dc field along [111] of 1.7 kV/cm or more is app lied. The criterion for glassiness is the apparition of a long-lived m etastable polarization, proportional to the applied field, without acc ompanying anomalies on the small-signal dielectric constant. It is bel ieved that the well-known broad dispersive maximum in epsilon(omega) n ear 270 K simply reflects thermal slowing down of strongly non-Debye d ynamics, and is not related to a ferroelectric phase transition; the e xistence of a divergence in the static dielectric constant is unlikely . A phase diagram in the electric-field-temperature plane is proposed.