A realization of excellent piezoelectricity and good thermal stability in CaBi2Nb2O9: Pseudo phase boundary

Phase boundaries (PBs) are known to contribute to the outstanding performances of lead-based and lead-free materials. However, a lack of PBs restricts the promotion of piezoelectric performance in bismuth layer-structured ferroelectrics (BLSFs). In this work, a pseudo PB, ie, pseudotetragonal distortion (regulated by Ce), is proposed to promote the piezoelectric properties of CaBi₂Nb₂O₉-based ceramics, and an excellent piezoelectric constant (d₃₃) of 20.2 pC/N with a high Curie temperature of 923°C is obtained. Verified Ce incorporation into the (Bi₂O₂)²⁺ layer alters the environment of the (Bi₂O₂)²⁺ layer, thereby influencing the atomic displacement in the Nb-O octahedron and modulating the theoretical spontaneous polarization (P_s). Strengthening of the pseudotetragonal distortion is favorable to the polarization switching, and maintains the theoretical P_s of ceramics at a high level, thus realizing the promotion of d₃₃. Furthermore, pseudotetragonal distortion guarantees good thermal depoling performance of the ceramic, which remains at 89.6% (18.1 pC/N) of its initial d₃₃ after depoling at 875°C. This work provides clear guidance on obtaining high d₃₃ and good thermal stability in BLSFs.