Polar metastability and an electric-field-induced phase transition in the disordered perovskite Pb(Mg1/3Nb2/3)O3

Abstract

We measure the effect of dc-electric-field–temperature sequences on the finite-frequency dielectric constant ɛ(ω), and the thermally stimulated depolarization current of single crystals of Pb (${\mathrm{Mg}}_{1/3}$ ${\mathrm{Nb}}_{2/3}$)${\mathrm{O}}_3$ (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 ɛ(ω) 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.