Browsing by Author "Delgado, Miguel"
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- Field dependence of glassy freezing in a relaxor ferroelectricDelgado, Miguel; Colla, Eugene V.; Griffin, P.; Weissman, Michael B.; Viehland, Dwight D. (American Physical Society, 2009-04-23)Multifrequency susceptibility measurements on the perovskite relaxor ferroelectric (PbMg(1/3)Nb(2/3)O(3))(0.88)(PbTiO(3))(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 PbMg(1/3)Nb(2/3)O(3), with grains too small to support large-scale internanoregion cooperativity.
- Kinetics and thermodynamics of the ferroelectric transitions in PbMg1/3Nb2/3O3 and PbMg1/3Nb2/3O3-12% PbTiO3 crystalsColla, Eugene V.; Jurik, Nathan; Liu, Yehan; Delgado, Miguel; Weissman, Michael B.; Viehland, Dwight D.; Ye, Zuo-Guang (American Institute of Physics, 2013-05-14)The two-step freezing and melting of the field-induced ferroelectric order in PbMg1/3Nb2/3O3 (PMN) and (PbMg1/3Nb2/3O3)(0.88)(PbTiO3)(0.12) (PMN-PT) is investigated. In PMN-PT, direct microscopic images show that both steps occur in the same spatial regions. The higher temperature freezing corresponds to the higher temperature melting, indicating that the stages are not just kinetically but also thermodynamically distinct. The higher-T melting step shows several indications of being a sharp first-order transition near an equilibrium temperature. The lower-T melting step shows more kinetic dependence. Partially poled PMN also spontaneously approaches saturation polarization on zero-field aging, indicating that the true equilibrium state is ferroelectric below similar to 200 K. In PMN-PT, a variety of kinetic measurements on the ferroelectric state indicate that the kinetics are governed by a glassy matrix showing aging effects. (C) 2013 AIP Publishing LLC.