Enhanced Piezoelectric Response and Temperature Stability in Gradient-Doped KNN-BiFeO₃ Ceramics

In our investigation of lead-free piezoceramics, we focus on gradient-doped potassium sodium niobate (K₀.₅Na₀.₅NbO₃, KNN) with bismuth ferrite (BiFeO₃, BFO) as a dopant. Compared to pure KNN, these gradient-doped ceramics demonstrate a marked enhancement in both temperature stability and piezoelectric performance. The compositional gradient of BiFeO₃ across bulk KNN significantly improves the piezoelectric coefficient (d₃₃), attributed to the combined effects of a polymorphic phase boundary (PPB) and the Maxwell-Wagner effect [1]. The variance in PPB across each layer provides a larger functional temperature range for the bulk ceramic. Additionally, inhomogeneous charge distribution at internal interfaces results in the Maxwell-Wagner effect, which amplifies the local electric field and enhances electromechanical coupling.