Defect-mediated domain-wall pinning induced by trace LiF doping: Ultrahigh Curie temperature and outstanding thermal stability in Bi4Ti3O12-based piezoceramics

Enhancing the Curie temperature ( T C ) in bismuth titanate (Bi 4 Ti 3 O 12 , BIT) based ceramics while maintaining robust piezoelectricity remains a longstanding challenge for high-temperature applications. Here, we demonstrate that trace LiF addition provides an effective route to simultaneously increase the T C by 30 °C and thermal stability of BIT-based piezoceramics. The optimized composition exhibits an ultrahigh T C of about 690 °C, a competitive piezoelectric coefficient ( d 33 ) of 34.5 pC/N and an outstanding resistivity of 2.6 × 10 7 Ω⋅cm at 500 °C. More importantly, over 88% of the initial d 33 is retained after annealing at 650 °C for 2 h. LiF addition induces a slight reduction in piezoelectric activity, and the accompanying reduced switching current and increased coercive field collectively indicate defect-mediated domain-wall pinning. Chemical etching and piezoresponse force microscopy further reveal that LiF addition alters domain configurations and suppresses domain-wall mobility, thereby stabilizing the poled state at elevated temperatures. These results provide a practical design route for high-temperature piezoceramics.