requirements of functionality and stabilization at high-temperature conditions. [5][6][7] Ferroelectric ceramics with the perovskite structure ABO 3 , such as BaTiO 3 , Pb(Zr,Ti)O 3 , and Pb(Mg 1/3 Nb 2/3 ) O 3 -PbTiO 3 , usually possess high piezoelectric constants d 33 (100-1500 pC N −1 ), but their Curie temperature T c is low (50-400 °C). [8,9] Thus, the usage range of the system is restricted to below 300 °C. Bismuth layer-structured ferroelectrics (BLSFs) have the general chemical formula (Bi 2 O 2 ) 2+ (A m-1 B m O 3m+1 ) 2− , and their structure is that (A m-1 B m O 3m+1 ) 2− perovskite layers are sandwiched between (Bi 2 O 2 ) 2+ fluorite-like layers along the c-axis. [10] Consequently, BLSFs piezoelectrics possess high Curie temperature T c (500-1000 °C), high mechanical quality factors, and low aging rates, which make them promising candidates for the hightemperature electronic industry. [11][12][13] Bismuth titanate, Bi 4 Ti 3 O 12 (BIT), is always regarded as an excellent candidate for high-temperature electromechanical systems owing to its high Curie temperature (T c is of 675 °C) as well as outbound spontaneous polarization (P s is of 50 µC cm −2 along the a-axis). [14][15][16] However, the piezoelectricity of BIT ceramics is poor (only 6-8 pC N −1 ) due to its strong anisotropic polarization, a large coercive field, and high leakage current. Extensive research has been made to acquire high-performance BITbased ceramics, including chemical modification and grain orientation techniques. [17][18][19][20][21][22][23] For example, a high d 33 of 21 pC N −1 and T c of 655 °C, as well as a lower dielectric loss of 0.3%,
High-temperature piezoelectric materials are widely needed in electromechanical sensors, actuators, and transducers that are exposed to high-temperature conditions. Bismuth layer-structured bismuth titanate (Bi 4 Ti 3 O 12 , BIT) ferroelectrics have a high Curie temperature of 675 °C but suffer from poor electrical properties, especially the piezoelectricity. Here, a giant piezoelectric coefficient d 33 of 40.2 pC N −1 is obtained in the Bi 3.97 Ce 0.03 Ti 2.98 (WNb) 0.01 O 12 ceramics with a high Curie temperature of 657 °C, the highest value reported to date in BIT-based piezoceramics. Electrical property and microstructural analysis reveal that the high piezoelectricity benefits from the preferential orientation of ferroelectric domains, the irreversibility of ferroelectric domain reorientation, and the high density of ferroelectric domain walls. Besides, excellent thermal stability of piezoelectric constant (d 33 = 36.7 pC N −1 at 500 °C, <10% variations in the range of room temperature to 500 °C), high electrical resistivity (ρ > 10 7 Ω cm at 500 °C), and low loss (tanδ < 1.5% at 500 °C) are also obtained in the Bi 3.97 Ce 0.03 Ti 2.98 (WNb) 0.01 O 12 ceramics. This work not only penetrates the origins of outstanding piezoelectricity of BITbased ceramics but also offers prospects for brand-new tactics to exploit high-performance high-temperature piezoceramics.
