A large coercive field (EC) and ultrahigh piezoelectricity are essential for ferroelectrics used in high-drive electromechanical applications. The discovery of relaxor-PbTiO3 crystals is a recent breakthrough; they currently afford the highest piezoelectricity, but usually with a low EC. Such performance deterioration occurs because high piezoelectricity is interlinked with an easy polarization rotation, subsequently favoring a dipole switch under small fields. Therefore, the search for ferroelectrics with both a large EC and ultrahigh piezoelectricity has become an imminent challenge. Herein, ternary Pb(Sc1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 crystals are reported, wherein the dispersed local heterogeneity comprises abundant tetragonal phases, affording a EC of 8.2 kV/cm (greater than that of Pb(Mg1/3Nb2/3)O3–PbTiO3 by a factor of three) and ultrahigh piezoelectricity (d33 = 2630 pC/N; d15 = 490 pC/N). The observed EC enhancement is the largest reported for ultrahigh-piezoelectric materials, providing a simple, practical, and universal route for improving functionalities in ferroelectrics with an atomic-level understanding.

Searching for lead-free piezoelectric materials with a large piezoelectricity and excellent thermal stability has been a major concern in both scientific research and practical applications. To understand the mechanism of high piezoelectricity and its temperature-dependent behavior in lead-free materials, we focus here on the tetragonal (K,Na,Li)(Nb,Ta)O3 single crystal and investigate the intrinsic d33* along arbitrary directions as well as its evolution with temperature. The synergistic influence of several factors (narrow tetragonal temperature interval, sharp tetragonal-cubic phase transition, and large PS below TC) leads to a strong anisotropy in the d33* profile, while a high d33* is obtained around θ = 45° over a wide temperature range. This work comprehensively reveals the physical mechanism of piezoelectric anisotropy in lead-free materials, which provides vital information to design high-performance lead-free piezoelectric materials through orientation engineering and lattice manipulation, which is expected to benefit a wide range of piezoelectric materials.

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Low-energy switching of ferroelectrics has been intensively studied for energy-efficient nanoelectronics. Mechanical force is considered as a low-energy consumption technique for switching the polarization of ferroelectric films due to the flexoelectric effect. Reduced threshold force is always desirable for the considerations of energy saving, easy domain manipulation, and sample surface protection. In this work, the mechanical switching behaviors of BaTiO3/SrRuO3 epitaxial heterostructure grown on Nb:SrTiO3 (001) substrate are reported. Domain switching is found to be induced by an extremely low tip force of 320 nN (estimated pressure ∼0.09 GPa), which is the lowest value ever reported. This low mechanical threshold is attributed to the small compressive strain, the low oxygen vacancy concentration in BaTiO3 film, and the high conductivity of the SrRuO3 electrode. The flexoelectricity under both perpendicular mechanical load (point measurement) and sliding load (scanning measurement) are investigated. The sliding mode shows a much stronger flexoelectric field for its strong trailing field. The mechanical written domains show several advantages in comparison with the electrically written ones: low charge injection, low energy consumption, high density, and improved stability. The ultralow-pressure switching in this work presents opportunities for next-generation low-energy and high-density memory electronics.

It has always been a hot topic to design an orderly mesoscopic structure in functional materials to tailor the macroscopic properties or realize new functions. The existence of domains in ferroelectric materials has been proven to affect the macroscopic properties, being actively studied in nonlinear optical conversion and piezoelectric effects. However, the high‐efficiency photoelectric conversion capability of ferroelectric crystals has not yet been explored. Here, the authors study the orderly arrangement of ferroelectric order in KTa1−xNbxO3 (KTN) perovskite crystals, and design the “head‐to‐head” domains by tuning the Curie temperature Tc, thereby generating abundant charged domain walls and robust conductive channels for electrons and holes. An ultrahigh ultraviolet photoresponsivity is achieved in the KTN crystal under zero bias voltage, being about four orders magnitude higher than that of the well‐known ferroelectric materials. The substantial improvement can be attributed to the judiciously designed ferroelectric order, as demonstrated by the conductive atomic force microscopy. In addition, KTN detector exhibits high stability and reliability after high‐temperature and fatigue treatment. KTN crystal features giant photoresponsivity, high electric–optical coefficient, and large χ(2) nonlinearity concurrently, indicating its great potential for application of all‐optical devices on photonic chips.