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.

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).