Relaxor ferroelectric single crystals, Dielectric, Piezoelectric, Neutron diffraction, Neutron pair distribution functions, Materials of engineering and construction. Mechanics of materials, TA401-492

The complex chemical and structural heterogeneity of relaxor ferroelectrics has made the origins of the giant piezoresponse extremely difficult to understand. Here, we successfully grew Ho-doped Pb(Mg1/3Nb2/3)O3–PbTiO3 (Ho-PMNT) single crystals with even higher d33, S33 and dielectric constant ε33/ε0 values of 3900 pC N−1, 0.34% and 15,000. We employed the in situ neutron diffraction to identify that the giant piezoelectric response of the Ho-PMNT originates from the composition near the tricritical triple point of a cubic paraelectric phase (C), ferroelectric monoclinic (M), and tetragonal (T) phases. It leads to a nearly polarization isotropy and thus facilitates polarization rotation between different ferroelectric states. The results of the neutron pair distribution function combined with aberration-corrected scanning transmission electron microscopy qualitatively analyze the angstrom-nanoscaled heterogeneities and their connection to local polarization. The Pb2+ displacement direction of is connected to the A site ordered polarization. There were also observed the different separation distances between the B-site atoms and the neighboring O atoms. It identifies the giant piezoelectric properties arise that the Ho-dopant immensely disrupt long-range polarization and enhance the local structural heterogeneity in the tricritical triple point.