Enhanced piezoelectricity in Na and Ce co-doped CaBi 4Ti 4O 15 ceramics for high temperature applications

The Na and Ce co-doped CaBi₄Ti₄O₁₅ (CBT) Aurivillius ceramics in a Ca_1-x(Na_0.5Ce_0.5)_xBi₄Ti₄O₁₅ (CNCBT, 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 on doping results from the increased tolerance factor t. The substitution-enhanced ferroelectric performance with large maximum polarization and facilitated domain switching is evidenced by the developed P-E and 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 remnant polarization and relatively high permittivity. In addition, multi-sized (micron and sub-micron) domain structures were observed in the CNCBT ceramics by piezoelectric response microscopy. 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 Curie point around 765 °C and high d₃₃ are suitable for high-temperature piezoelectric applications.