Achieving giant electrostrain of above 1% in (Bi,Na)TiO ₃ -based lead-free piezoelectrics via introducing oxygen-defect composition

Abstract

Piezoelectric ceramics have been extensively used in actuators, where the magnitude of electrostrain is key indicator for large-stroke actuation applications. Here, we propose an innovative strategy based on defect chemistry to form a defect-engineered morphotropic phase boundary and achieve a giant strain of 1.12% in lead-free Bi 0.5 Na 0.5 TiO 3 (BNT)–based ceramics. The incorporation of the hypothetical perovskite BaAlO 2.5 with nominal oxygen defect into BNT will form strongly polarized directional defect dipoles, leading to a strong pinning effect after aging. The large asymmetrical strain is mainly attributed to two factors: The defect dipoles along crystallographic [001] direction destroy the long-range ordering of the ferroelectric and activate a reversible phase transition while promoting polarization rotation when the dipoles are aligned along the applied electric field. Our results not only demonstrate the potential application of BNT-based materials in low-frequency, large-stroke actuators but also provide a general methodology to achieve large strain.

Outstanding Energy-Storage Density Together with Efficiency of above 90% via Local Structure Design

“…The X-ray diffraction (XRD) reflection and selected area electron diffraction (SAED) characterization (Figures S4a and S9) of H8 confirmed the average structure of the cubic-like phase, and the origin of the relaxor was not well demonstrated. Meanwhile, the microscopic domain structure exhibited polar nanoregions (Figures S9 and S10), which indicated macroscopic relaxor characteristics . The results indicated that the local structure and macroscopic performance were related to each other.…”

“…Meanwhile, the microscopic domain structure exhibited polar nanoregions (Figures S9 and S10), which indicated macroscopic relaxor characteristics. 34 The results indicated that the local structure and macroscopic performance were related to each other. Thus, the atomic-scale local structure of H8 was further probed via high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM).…”

“…Taking the morphotropic phase boundary (MPB) of BNT–BT as an example, the modification in the MPB has always been the main basis for regulating high piezoelectric performance. − However, the MPB (6–10% BT) does not appear to be a good choice for realizing high energy-storage performance. The reason is that the extensive phase transition from the weakly polar P 4 bm phase to the R 3 c phase usually ends with a relatively large hysteresis, which is not beneficial for achieving high efficiency .…”

Establishing a Relationship between the Piezoelectric Response and Oxygen Vacancies in Lead-Free Piezoelectrics

“…For piezoelectric ceramics, lead-free alternatives have clearly captured the attention of researchers in recent years due to environmentally friendly development strategies and the pressure from the Restriction of Hazardous Substance (RoHS) and the Waste Electrical and Electronic Equipment (WEEE) Directive . Among lead-free piezoelectric systems, niobium- and bismuth-based ceramics have achieved great achievements; − however, the complete replacement for lead-based systems still needs further efforts. − As promising candidates for high-temperature lead-free piezoceramics, BiFeO 3 –BaTiO 3 (BF–BT) ceramics with high Curie temperatures ( T C ) of over 600 °C and much better piezoelectric properties have become desired materials for high-temperature applications of piezoelectric sensors compared to bismuth layered structure and tungsten bronze structure systems. − …”

Ferroelectric–Ferroelastic Transitions in (Na0.5Bi0.5)TiO3-BaTiO3 Single Crystals

“…Among the various types of lead-free perovskite ferroelectric materials, the Na 0.5 Bi 0.5 TiO 3 (NBT) system has been widely investigated in the past few decades because of its excellent piezoelectric properties, especially the large electrostrain. − The relaxation characteristics of NBT-based solid solutions such as Na 0.5 Bi 0.5 TiO 3 -BaTiO 3 (NBT-BT) and Na 0.5 Bi 0.5 TiO 3 -K 0.5 Bi 0.5 TiO 3 (NBT-KBT), as well as the electric field-induced relaxor–ferroelectric phase transition provide great potential for the optimization of piezoelectric properties. − NBT-based materials also present hierarchical structural features, including oxygen octahedra tilting and superlattice diffractions, , various domain structures, , and special polar nanoregions (PNRs). , The studies of these hierarchical structures may provide the basis for designing high-performance piezoelectric and ferroelectric materials, which is an important topic in condensed matter physics and materials science.…”