Macroscopic polarization in the nominally ergodic relaxor state of lead magnesium niobate

Macroscopic polarity and its dynamic response to external electric fields and temperature in the nominally ergodic relaxor phase of pristine lead magnesium niobate crystals and ceramics, Pb(Mg1/3Nb2/3)O3 (PMN), were investigated. Dynamic pyroelectric measurements provide evidence for persistent macroscopic polarity of the samples. Annealing experiments below and above Burns temperature of polarized samples relate this polarity to the presence of polar nano-entities and their dynamics. The dc electric field strength required for macroscopic polarization reversal is similar to the amplitude of the ac field where dynamic nonlinear dielectric permittivity reaches its maximum. Consequently, the aforementioned maximum is related to the reorientation of polar nano-entities. The results question the existence of an ergodic state in PMN below Burns temperature

Domain wall-grain boundary interactions in polycrystalline Pb(Zr0.7Ti0.3)O3 piezoceramics

Interactions between grain boundaries and domain walls were extensively studied in ferroelectric films and bicrystals. This knowledge, however, has not been transferred to polycrystalline ceramics, in which the grain size represents a powerful tool to tailor the electromechanical and dielectric response. Here, we relate changes in dielectric and electromechanical properties of a bulk polycrystalline Pb(Zr0.7Ti0.3)O3 to domain wall interactions with grain boundaries. Samples with grain sizes in the range of 3.9–10.4 μm were prepared and their microstructure, crystal structure, and dielectric/electromechanical properties were investigated. A decreasing grain size was accompanied by a reduction in large-signal electromechanical properties and an increase in small-signal relative permittivity. High-energy diffraction analysis revealed increasing microstrains upon decreasing the grain size, while piezoresponse force microscopy indicated an increased local coercive voltage near grain boundaries. The changes in properties were thus related to strained material volume close to the grain boundaries exhibiting reduced domain wall dynamics