Domain Structure Evolutions During the Poling Process for ‐Oriented PMN–xPT Crystals Across the MPB Region
The poling effect on the ‐oriented (1−x)Pb(Mg1/3Nb2/3)O3‐xPbTiO3 (PMN–xPT) single crystals across the morphotropic phase boundary (MPB) was studied. The dielectric and piezoelectric properties were investigated as a function of the poling field. Domain structure evolutions during the poling process were recorded. In the unpoled PMN–xPT phase diagram, an apparent rhombohedral (R)‐tetragonal (T) phase boundary exists. With room‐temperature poling, the structure transformation sequence strongly depends on the composition. The crystal experiences a direct transition to the 2R/2T domain state in the rhombohedral or tetragonal phase field beyond the MPB region, whereas within the MPB zone it is hard to achieve the 2R/2T engineered configuration although the initial state is either rhombohedral or tetragonal as well. The piezoelectric responses of the MPB·PMN–xPTs are extraordinary weak (d 33 ~ 250 pC/N), in contrast to the ‐oriented multidomain PMN–xPTs with ultrahigh‐piezoelectric coefficient (d 33 > 1000 pC/N). We demonstrate that a slight composition variation near the MPB will significantly influence the domain evolution route and piezoelectricity for the ‐oriented PMN–xPT crystals. We also confirm the feasibility to realize the 2R/2T engineered domain configuration for the ‐oriented MPB crystals, which will extend the desired portion of the Bridgeman‐grown boules with optimal piezoelectric properties.
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