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Flexoelectricity yields electric polarization through graded strains and exists in various kinds of solid dielectrics but usually with a weak coupling response. In this letter, several Bi-doped Pb(Mg2/3Nb1/3)O3-xPbTiO3 (PMN-xPT) ferroelectric ceramics were prepared and the interplay of their piezoelectricity and flexoelectricity was systematically investigated. The largest flexoelectric response (∼300 μC/m) was 30 times larger than that of pure PMN-PT and was observed in the Bi-doped PMN-32PT, where the after poling piezoelectric coefficients were also the largest (990 pC/N) among all the compositions. This suggests that the apparent flexoelectricity in ferroelectrics is highly related to the bulk piezoelectricity. Therefore, introducing a local structural heterogeneity is considered as a feasible approach to achieve an ultrahigh piezoelectric response while also providing an ultrahigh flexoelectricity. [ABSTRACT FROM AUTHOR]

Low driving voltage is important for miniaturization and untethered service of millirobots made of piezoelectric materials. In this research, we designed a bio-inspired bimorph-structured millirobot with a transparent relaxor ferroelectric crystal. Due to the ultrahigh piezoelectricity of the relaxor ferroelectric crystals and the optimized bimorph-based structure, the millirobot shows a maximum moving speed up to 9.22 b s−1 (body length per second) at 100 V, while the minimum driving voltage for initial movement can be as low as 3 V, which is more than two orders of magnitude smaller than that of millirobot based on dielectric elastomers. The maximum and minimum power consumptions of the millirobot are 71.6 mW and 85.9 μW, respectively. The robustness of the millirobot is reflected in its mechanical load stability carrying a 78 g mass (97.5 times of its weight) and its cryogenic tolerance. This work is believed to be beneficial to the design of various robust electromechanical devices with low driving voltage. [ABSTRACT FROM AUTHOR]