Superior Piezoelectric Performance in Textured CaBi2Nb2O9 Ferroelectric Ceramics through Rare-Earth Gadolinium Doping and Spark Plasma Sintering.

High-performance piezoelectric ceramics with excellent thermal stability are crucial for high-temperature piezoelectric sensor applications. However, conventional fabrication processes offer limited enhancements in piezoelectric performance. In this study, we achieved a significant breakthrough in the piezoelectric performance of highly textured CaBi2Nb2O9 (CBN) ceramics by incorporating rare-earth gadolinium doping and utilizing spark plasma sintering. The resulting Ca0.97Gd0.03Bi2Nb2O9 (CBN-3Gd) ceramics exhibited superior piezoelectric properties, with a high piezoelectric constant d33 of 26 pC/N and a high Curie temperature TC of 946 °C. We employed piezoresponse force microscopy (PFM) to observe the morphology and dimensions of the ferroelectric domains, revealing a rod-shaped 3D domain configuration. This configuration facilitated polarization rotation in the textured ceramics, as analyzed using X-ray photoelectron spectroscopy (XPS) and polarization-electric field (P-E) hysteresis loops. Furthermore, the textured CBN-3Gd ceramics demonstrated exceptional thermal stability and reliability. The piezoelectric constant d33 decreased by only 11.8% over a temperature range of room temperature to 500 °C, and the DC electrical resistivity remained at 6.7 × 105 Ω cm at 600 °C. This work not only highlights the great potential of textured CBN-based ceramics for high-temperature piezoelectric sensors but also provides a viable strategy for enhancing the performance of piezoelectric materials with large aspect ratio micromorphology.

Revealing the Mutually Enhanced Mechanism of Necroptosis and Immunotherapy Induced by Defect Engineering and Piezoelectric Effect.

Owing to low immunogenicity-induced immune escape and short-term circulating immune responses, the efficiency of immunotherapy is unsatisfactory. Therefore, triggering immunogenic cell death and establishing a long-term, mutually reinforced treatment modality are urgent challenges. In this study, ultrathin CaBi2 Nb2 O9 nanosheets with tunable oxygen vacancies (abbreviated as CBNO-OV1) are prepared for synergistic necroptosis and immunotherapy. The optimized vacancy concentration significantly improves the piezoelectric effect under ultrasound irradiation, thereby considerably improving the generation of reactive oxygen species (ROS). Density functional theory shows that oxygen vacancies can improve the efficiency of electron hole separation by suppressing their recombination, thus resulting in enhanced piezocatalytic activity. Moreover, the piezoelectric effect improves the permeability of tumor cell membranes, thus resulting in Ca2+ influx. Additionally, CBNO-OV1 also releases a portion of Ca2+ , which induces necroptosis assisted by explosive ROS. Ribonucleic acid transcription tests suggest the mechanisms associated with immune response activation and necroptosis. More importantly, necroptosis can trigger a significant immune response in vivo, thus activating macrophage M1 polarization through the NF-kappa B pathway and promoting T-cell differentiation.Tumor Necrosis Factor-α differentiated from macrophages conversely promotes necroptosis, thus realizing a mutually enhanced effect. This study demonstrates the feasibility of mutually reinforced necroptosis and immunotherapy for amplifying tumor efficacy.

Strain Engineered CaBi2Nb2O9 Thin Films with Enhanced Electrical Properties.

In this work, strain engineered polycrystalline thin films (∼250 nm) of bismuth layer-structured ferroelectric (BLSF) CaBi2Nb2O9 (CBNO) were prepared by using a radio frequency (RF) magnetron sputtering technique. XRD analysis revealed that the films were (200)/(020) and (00l) textured with a large in-plane tensile stress. Cross-sectional TEM analyses confirmed the bismuth layered-structure, as well as crystalline orientations and a strain-controlled growth mode of the grains. Result of a quantitative XPS analysis revealed that the composition of the film is close to the chemical stoichiometry. Excellent electrical properties were achieved in the CBNO films, including a high dielectric constant (∼280 @5 kHz), a small dielectric loss (tgδ ≤ 1.6% up to an applied electric field of ∼1200 kV/cm) and a large polarization (Pr ≈ 14 µC/cm(2) @ 1 kHz).