Mechanisms underpinning the ultrahigh piezoelectricity in Sm-doped 0.705Pb(Mg1/3Nb2/3)O3-0.295PbTiO3: Temperature-induced metastable local structure and field-induced polarization rotation.

The solid solution of (100 − x)%Pb(Mg1/3Nb2/3)O3-x%PbTiO3 (PMN-xPT) exhibits ultrahigh piezoelectric and dielectric properties near the morphotropic phase boundary compositions and, thus, has been extensively studied in recent years. Recently, 2.5 mol. % Sm-doped PMN-29PT polycrystalline ceramics were reported to possess the highest piezoelectric coefficients (∼1500 pC/N) among all reported piezoceramics, but the atomic-scale mechanisms for such high piezoelectric properties are not yet clear. In this paper, in situ X-ray diffraction and X-ray total scattering measurements during the application of an electric field, together with in situ total scattering measurement at different temperatures, were conducted for 2.5 mol. % Sm-doped PMN-29.5PT (2.5Sm-PMN-29.5PT). Both the largest field-induced strain and the piezoelectric response were found in the crystallites oriented with their ⟨ 100 ⟩ PC directions parallel to the applied field. The local Pb displacement was analyzed using the reverse Monte Carlo method based on the pair distribution functions at different temperatures, where a temperature-induced directional change of Pb displacement was observed. Based on the experimental observations, a field-induced polarization rotation is suggested to be the dominant mechanism for the ultrahigh piezoelectricity of the 2.5Sm-PMN-29.5PT ceramic, while the ease of polarization rotation is possibly attributed to the temperature-induced metastable local monoclinic symmetries with their polar axes close to ⟨ 111 ⟩ PC . [ABSTRACT FROM AUTHOR]