Dual Achievements of Piezoelectric Enhancement and Temperature Sensing in Bi ₄ Ti ₃ O ₁₂ Ceramics via Er ³⁺ Doping

Abstract The multifunction sensing materials can greatly reduce the complexity of the sensing system when used in the constrained spaces. Bismuth layer‐structured ferroelectric Bi 4 Ti 3 O 12 (BIT) is expected to own dual functionality of simultaneous piezoelectric vibration monitoring and temperature detection when they are used in jet engines and nuclear reactors. Bi 4– x Er x Ti 2.98 (W/Nb) 0.01 O 12 (BNWT: x Er, x = 0, 0.01, 0.03, 0.05 and 0.1) ceramics are developed with an optimal piezoelectric coefficient d 33 of 36 pC N −1 and a high Curie temperature of 657 °C. Er 3+ doping can significantly enhance the piezoelectric and ferroelectric properties of the BNWT: x Er without sacrificing Curie temperature. The introduction of Er 3+ can effectively reduce the formation of oxygen vacancies and the difference in lattice constants a , b , and c . The enhanced piezoelectric properties in the BNWT:0.03Er are related to the reduced oxygen vacancy concentration and orthogonal distortion. Most significantly, the incorporation of Er 3+ imparts optical temperature sensing functionality to the ceramics in a broad range (173–773 K) via the fluorescence intensity ratio (FIR) technique, with luminescence color changes enabling high‐temperature early‐warning capability. This dual functionality of piezoelectric vibration monitoring and optical temperature sensing achieved by Er 3 ⁺ doping provides a novel integrated sensing solution for in situ condition monitoring in extreme environments.