Enhanced piezoelectric properties and thermal stability in donor-acceptor co-doped BaTiO₃ ceramics

Lead-free piezoelectric ceramics are widely used in actuators, sensors, and transducers due to high piezoelectric coefficients and thermal stability. However, the commonly used strategies for improving the piezoelectric coefficients, such as morphotropic phase boundary (MPB) and polymorphic phase transition (PPT), are ineffective in improving temperature stability. In this work, defect dipoles were introduced into barium titanate to enhance both its piezoelectric coefficient and temperature stability. Donor Nb⁵⁺ and acceptor Li⁺ were doped into BaTiO₃ as defect dipoles, resulting in an increase of piezoelectric coefficient to 267 pC/N and a significant improvement in thermal stability. The decrease in flat free energy and grain size, induced by the doping effect, led to a rise in piezoelectric coefficient. Furthermore, the defect dipoles produce an internal bias field (E_i), thus improving thermal stability by stabilizing the domain. This research provides a hopeful strategy for lead-free piezoelectric ceramics with both high thermal stability and a large dielectric coefficient.