Field dependence of glassy freezing in a relaxor ferroelectric

Multifrequency susceptibility measurements on the perovskite relaxor ferroelectric (PbMg1/3 Nb2/3 O3) 0.88 (PbTiO3) 0.12 were performed at various strengths of dc electric field applied along the [111] direction. The temperature-frequency dependences fit the Vogel-Fulcher form, allowing the extraction of a frequency-independent glassy freezing temperature. These Vogel-Fulcher temperatures showed significant reductions in applied fields, following an empirical Gabay-Toulouse form, similar to vector spin glasses. The magnitude of the sensitivity indicates that the glassy state is formed by interactions among the same entities which account for the susceptibility, i.e., the polar nanoregions. That interpretation is supported by other data showing a loss of Vogel-Fulcher behavior in a powder sample of PbMg1/3 Nb2/3 O3, with grains too small to support large-scale internanoregion cooperativity.