Improved Dielectric and Piezoelectric Response in Defect‐Mediated (Na _0.5 Bi _0.5 )TiO ₃ ‒BaAlO _2.5 Piezoceramics

ABSTRACT Piezoceramics based on (Na 0.5 Bi 0.5 )TiO 3 have garnered considerable attention over the past decade due to the remarkable properties observed near the morphotropic phase boundary (MPB). The piezoelectric response ( d 33 ) is inversely related to the ferroelectric–relaxor ( T F‐R ) or depolarization ( T d ) phase transition temperature. It has been suggested that the introduction of oxygen defects can elevate the T d while reducing the d 33 . In contrast, our investigation on the (Na 0.5 Bi 0.5 )TiO 3 ‒ x BaAlO 2.5 solid solution (via introducing oxygen defects) revealed a decrease in T d and a corresponding increase in d 33 , reaching a maximum of approximately ∼151 pC/N. This counterintuitive phenomenon has been linked to a notable increase in the number of interfaces or domain wall density, which compensates for a reduction in lattice structural distortion.