Spark plasma sintering of high-TC calcium bismuth niobate (CaBi2Nb2O9) with superior piezoelectric performance

Calcium bismuth niobate (CaBi₂Nb₂O₉) is a promising ceramic material for high-temperature piezoelectric applications due to its high Curie temperature (T_C) of 940 °C. However, its practical use is limited by poor piezoelectric performance and low direct-current (DC) electrical resistivity at elevated temperatures. In this study, we introduced pseudo-tetragonal distortion into CaBi₂Nb₂O₉ by substituting rare-earth thulium ions, which reduced domain wall energy, facilitated domain switching, and decreased the presence of oxygen vacancies. These enhancements significantly improved both the piezoelectric performance and DC electrical resistivity of the material. To further enhance piezoelectric performance, we prepared textured thulium-substituted CaBi₂Nb₂O₉ ceramics with a Lotgering factor (f) of up to 77.4 % using a two-step spark plasma sintering method. The resulting textured CaBi₂Nb₂O₉ ceramics exhibited superior piezoelectric performance, with a piezoelectric constant d₃₃ of 25.2 pC/N, four times higher than that of non-textured CaBi₂Nb₂O₉. Importantly, these textured ceramics maintained excellent electrical properties at elevated temperatures, suggesting their suitability for high-temperature piezoelectric device applications.