Simultaneous Enhancement of Piezoelectricity and Temperature Stability in KNN‐Based Lead‐Free Ceramics Via Layered Distribution of Dopants

Abstract

Abstract The past two decades have seen a great enhancement of piezoelectric coefficients ( d 33 ) to higher than 570 pC/N in (K, Na)NbO 3 (KNN) piezoelectrics, but one notoriously unresolved issue is their severe temperature instability, obstructing them toward practical applications. The present work demonstrates a facile approach to overcome this problem by introducing a layered distribution of key dopants (Li and Sb) in a monolithic ceramic, featuring stepwise varied polymorphic phase transition (PPT) temperatures along the thickness direction. The dopant‐graded ceramic exhibits an outstanding d 33 of 508 pC/N and a very large piezoelectric strain ( S uni , of 0.18%). More importantly, an excellent temperature stability ( d 33 variation within 13% over the temperature range of 25–150 ° C) is achieved, which is superior to that of most state‐of‐art KNN counterparts. These are attributed to the construction of spatially diffused PPT in combination with enhanced polarization, permittivity, and piezoresponse through interfacial effect, including the Maxwell–Wagner effect and intergranular stress by gradient doping. The results offer an alternative strategy for designing high‐performance piezoelectric materials with desirable temperature reliability.