The piezoelectric enhancement was attributed to the local structural disorder introduced by the donor dopant 13, adding up to the already present disorder inherent to RE materials 14. 1c, i.e., 1500 pC/N for Sm-doped versus 650 pC/N for undoped PMN–PT ceramics). With the strongest effect achieved using Sm doping, the authors reported on piezoelectric coefficients exceeding 1500 pC/N, which is more than doubled with respect to the response of the morphotropic undoped PMN–PT ceramics (see the maximum d 33 values at the MPB in the two plots of Fig. PT-based RE-FE crystals has recently been overshadowed by the discovery of ultrahigh piezoelectricity in rare-earth doped PMN–PT ceramics 12. As one of the points of discussion later in this contribution, it is important to emphasized that the polarization rotation in PMN–PT and similar RE-FEs is not as simple as that in FE PZT because it is complicated by the disordered polar structure inherent to RE-based compositions (see next section for details). Following the discoveries of the bridging monoclinic phases at MPBs in PZT and PMN–PT 10, the concept of polarization rotation has been universally used to explain MPB property enhancement 11. 1b), resulting in large piezoelectric coefficients measured in compositions close to the MPB (Fig. Therefore, by applying an electric field on the R crystal along its off-polar pc direction, the field-driven rotation of the pc R polarization vector toward the pc T direction becomes easier in the proximity of the T phase (see inset of Fig. A simpler phenomenological approach later explained that the propensity for the polarization rotation has its origin in the structural instability related to the proximity of rhombohedral (R) and tetragonal (T) phases close to the MPB 9. The large response was initially explained by first-principles computations using the concept of polarization rotation 8. 7 reported on the unusually large piezoelectric response (piezoelectric coefficient up to ~2500 pC/N) of PMN- and PZN-based rhombohedral crystals when measured along non-polar axis and in the vicinity of the morphotropic phase boundary (MPB see red arrow in Fig. 7 by permission from John Wiley & Sons and AIP Publishing, respectively.Ī true interest in RE-FE single crystals began in 1997 when Park et al. Figures shown in ( a) and ( b) were reprinted from Ref. The data for undoped and Sm-doped PMN–PT were reproduced from Kelly et al. c Piezoelectric d 33 coefficient of PMN–PT ceramics as a function of PT content for undoped and Sm-doped ceramic samples, illustrating the ultrahigh piezoelectricity achieved by Sm doping. The upper inset shows schematically the mechanism responsible for the large response, i.e., the easy rotation of the R pc polarization vector (pc denotes pseudo cubic) toward the tetragonal (T) pc polar direction in the case of the electric field (E) applied along pc (see text for detailed explanation). The source of the d 33 data is reported in the original paper (Ref. b Piezoelectric d 33 coefficient of RE-FE Pb(Zn 1/3Nb 2/3)O 3–PbTiO 3 (PZN-PT) single crystals as a function of composition (PT content) and orientation (with respect to applied electric field), illustrating the large response of -oriented rhombohedral (R) crystals close to the morphotropic phase boundary (MPB) region 7 (see red arrow). Among other useful properties of RE-FEs, the large permittivity over a broad temperature range is advantageous in diverse application areas, such as energy storage 4, electrocaloric cooling 5 and electrostrictive actuation 6.Ī Frequency dispersion of the temperature-dependent dielectric permittivity (ε’) maximum of PMN single crystal, representing the characteristic feature of RE-based materials 1, 3. In contrast to “normal” FEs, canonical REs are distinguished by the temperature-dependent dielectric permittivity maximum that is typically broad and frequency dispersed (Fig. The most discussed is the pseudo-binary (1–x)Pb(Mg 1/3Nb 2/3)O 3–xPbTiO 3 (PMN–PT) solid solution where PMN and PT are the RE and FE end-members, respectively (note that throughout this paper PMN–PT will be in the focus and the terms “RE” and “RE-FE” will specifically refer to lead-based perovskite compositions). The group of RE-FEs includes a vast range of organic and inorganic materials, as well as lead-based and lead-free oxide compositions of various structural types 1, 2, 3. After more than seven decades of studies we are back in the era of relaxor ferroelectrics (FEs), a group of materials consisting of the unique combination of a disordered relaxor (RE) component and a long-range-ordered FE component.
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