Defect engineering of oxygen vacancies and domain configuration for high-performance CaBi₄Ti₄O₁₅ piezoelectric ceramics

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.