Bismuth-layer-structured ferroelectrics (BLSFs) are promising candidates for high-temperature piezoelectric applications owing to their intrinsically high Curie temperatures. However, their practical implementation is hindered by the relatively low piezoelectric activity, which is largely associated with oxygen-vacancy-induced pinning of ferroelectric domain walls. Herein, a donor–acceptor defect engineering strategy is proposed to regulate oxygen vacancies and domain structures in CaBi₄Ti₄O₁₅ through non-equivalent co-doping. The simultaneous introduction of Cr³⁺ and Ta⁵⁺ into the B-site can effectively increase local lattice distortion, reduce oxygen vacancy concentration, and form defect dipoles to suppress the thermally activated migration of oxygen vacancies, thereby increasing intrinsic polarization contribution, facilitating domain-wall motion, and enhancing the piezoelectric response. As a result, the optimized CaBi₄Ti_3.96(Cr_1/3Ta_2/3)_0.04O₁₅ ceramic exhibits a high Curie temperature (T_c) of 792 ℃, a DC resistivity of 9.5×10⁶ Ω·cm at 500 ℃, and a piezoelectric coefficient (d₃₃) of 25.7 pC/N, while retaining 23.3 pC/N after annealing at 600 ℃. Multiscale structural characterization reveals that the enhanced piezoelectric performance originates from the increased intrinsic polarization contribution and the synergistic regulation of oxygen-vacancy behavior coupled with the formation of high-density stripe domain structures. This work provides an effective defect-engineering strategy for developing high-performance BLSFs piezoelectric ceramics for harsh-environment applications.

For Bi₄Ti₃O₁₂ (BIT) high-temperature piezoceramics, improving piezoelectric performance often comes at the expense of a reduced Curie temperature. In this study, a series of Bi_4−xCe_xTi_2.97(Cr_1/3Ta_2/3)_0.03O₁₂ (x = 0, 0.02, 0.04, 0.06, and 0.08) ceramics were synthesized using the solid-state reaction method, and their phase structure, microstructure, piezoelectric properties, and conduction mechanisms were systematically analyzed. By employing a B-site non-equivalent co-doping strategy and introducing Ce ions into the A-site, we achieve a synergistic increase in the piezoelectric performance, Curie temperature, and high-temperature resistivity of BIT-based ceramics. This A/B site multi-co-doping significantly enhances the electrical properties by reducing the oxygen vacancy concentration. Notably, the ceramics with x = 0.04 exhibit a high piezoelectric coefficient (d₃₃) of 37 pC·N⁻¹, excellent resistivity of 6.6×10⁶ Ω·cm at 500 °C, and a high Curie temperature of 681 °C. Piezoelectric force microscopy and phase field simulation reveal that the superior piezoelectric performance arises from larger domain sizes, a stronger response to external electric fields, and a higher breakdown field strength. These findings not only position this material as a robust candidate for high-temperature applications but also provide valuable insights into the design of piezoelectric ceramics with enhanced stability and performance.

Electrobending, an emerging phenomenon in electroactive ceramics, has recently attracted significant interest; however, existing measurement methods often confound electrotensile and electrobending strains, leading to ambiguity. This study distinguishes electrotensile and electrobending strains in K_0.5Na_0.5NbO₃ (KNN) ceramics by examining their thickness, frequency, temperature, and directional dependency, identifying a critical thickness threshold of 600 μm for electrobending in samples of 8.5 mm diameter. This threshold establishes a clear distinction between electrotensile and electrobending within the KNN system and provides a benchmark that can be applied to other systems through similar methodologies. Additionally, new electrobending parameters have been defined to assess bending deformation, addressing recent misinterpretations of “giant strain” and advancing electrostrain research by introducing an electrobending framework.

In this study, (Cr_1/3/Ta_2/3) non-equivalent co-doped Bi₄Ti₃O₁₂ (BIT) ceramics were prepared to solve the problem that high piezoelectric performance, high Curie temperature, and high-temperature resistivity could not be achieved simultaneously in BIT-based ceramics. A series of Bi₄Ti_3−x(Cr_1/3Ta_2/3)_xO₁₂ (x = 0–0.04) ceramics were synthesized by the solid-state reaction method. The phase structure, microstructure, piezoelectric performance, and conductive mechanism of the samples were systematically investigated. The B-site non-equivalent co-doping strategy combining high-valence Ta⁵⁺ and low-valence Cr³⁺ significantly enhances electrical properties due to a decrease in oxygen vacancy concentration. Bi₄Ti_2.97(Cr_1/3Ta_2/3)_0.03O₁₂ ceramics exhibit a high piezoelectric coefficient (d₃₃ = 26 pC·N⁻¹) and a high Curie temperature (T_C = 687 ℃). Moreover, the significantly increased resistivity (ρ = 2.8×10⁶ Ω·cm at 500 ℃) and good piezoelectric stability up to 600 ℃ are also obtained for this composition. All the results demonstrate that Cr/Ta co-doped BIT-based ceramics have great potential to be applied in high-temperature piezoelectric applications.

(Bi_0.5Na_0.5)TiO₃ (BNT)-based lead-free piezoceramics exhibit excellent electric field-induced strain (electrostrain) properties, but often suffer from large hysteresis and poor fatigue resistance, which strongly limit their applications. Here, <00l> textured Nb⁵⁺-doped 0.8(Bi_0.5Na_0.5)TiO₃–0.2(Bi_0.5K_0.5)TiO₃ (0.8BNT–0.2BKT) ceramics with a high degree of texturing (~80%) were prepared by the reactive template grain growth (RTGG) method using Bi₄Ti₃O₁₂ as a template. By the combination of donor doping in the B-site and the RTGG method, the electrostrain performance achieves a significant enhancement. A high electrostrain of 0.65% and a piezoelectric coefficient ( $d_{33}^{*}$) of 1083 pm/V with reduced hysteresis at an electric field of 6 kV/mm are obtained. No electrostrain performance degradation is observed after unipolar electric field loading of 10⁵ cycles, showing excellent fatigue endurance. These results indicate that the texturing BNT-based lead-free piezoceramics by the RTGG method is a useful approach to developing eco-friendly actuators.