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

We measure the effect of dc-electric-field-temperature sequences on the finite-frequency dielectric constant epsilon(omega), and the thermally stimulated depolarization current of single crystals of Pb (Mg1/3Nb2/3)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 applied. The criterion for glassiness is the apparition of a long-lived metastable polarization, proportional to the applied field, without accompanying anomalies on the small-signal dielectric constant. It is believed that the well-known broad dispersive maximum in epsilon(omega) near 270 K simply reflects thermal slowing down of strongly non-Debye dynamics, and is not related to a ferroelectric phase transition; the existence of a divergence in the static dielectric constant is unlikely. A phase diagram in the electric-field-temperature plane is proposed.