Ferroelectric stability and fatigue mechanism of BNKT ceramics by Nb doping

The fatigue behavior of Bi_0.5Na_0.4K_0.1TiO₃-based ceramics depends on the polarity. While the non-ergodic relaxor ceramics have large residual polarization but poor fatigue behavior, the ergodic relaxor ceramics have excellent fatigue resistance but tiny residual polarization. Therefore, obtaining ferroelectric ceramics with high residual polarization and excellent fatigue resistance is challenging due to the trade-off between non-ergodic relaxor and ergodic relaxor. Here, we modulate the free energy barrier by doping relaxant Nb to achieve the coexistence of non-ergodic and ergodic relaxor phases. At 0.6% Nb doping, the residual polarization is large at 2P_r = 49.3 µC/cm², increased to 54.23 µC/cm² after 10² cycles and decreased to 53.04 µC/cm² after 10⁵ cycles, indicating good fatigue resistance behavior. The large residual polarization is due to the metastable ferroelectric state, while the excellent fatigue resistance may be attributed to the field-induced ferroelectric-relaxor phase transition.