Enhanced piezoelectricity in Na and Ce co-doped CaBi₄Ti₄O₁₅ ceramics for high-temperature applications

The sodium (Na) and Ce co-doped calcium bismuth titanate (CBT; CaBi₄Ti₄O₁₅) Aurivillius ceramics in a Ca_1−x(Na_0.5Ce_0.5)_xBi₄Ti₄O₁₅ (CNCBT; doping content (x) = 0, 0.03, 0.05, 0.08 and 0.12) system were synthesized by the conventional solid-state sintering method. All compositions show a single-phase orthorhombic (space group: A2₁am) structure at room temperature. The shift of the Curie point (T_C) towards lower temperatures (T) on doping results from the increased tolerance factor (t). The substitution-enhanced ferroelectric performance with large maximum polarization (P_m) and facilitated domain switching is evidenced by the developed electrical polarization–electric field (P–E) and electrical current–electric field (I–E) hysteresis loops. The piezoelectric coefficient (d₃₃ = 20.5± 0.1 pC/N) of the x = 0.12 sample is about four times larger than that of pure CBT. The improved piezoelectric properties can be attributed to the high remanent polarization (P_r) and relatively high dielectric permittivity (ε′). In addition, multi-sized (micron and sub-micron) domain structures were observed in the CNCBT ceramics by the piezoresponse force microscope (PFM). The multiple-sized ferroelectric domain structure with smaller domains is beneficial to the easy domain switching, enhanced ferroelectric performance, and improved piezoelectric properties of the CNCBT ceramics. The designed Aurivillius-phase ferroelectric ceramics with the T_C around 765 ℃ and high piezoelectric coefficient (d₃₃) are suitable for high-temperature piezoelectric applications.