High mechanical quality factor and high piezoelectric coefficient achieved via acceptor-modified invisible boundary

High mechanical quality factor (Q_m) and high piezoelectric coefficient (d₃₃) are desired for high-power applications of piezoelectric ceramics. However, achieving them based on currently known mechanisms has proven challenging because of the tradeoff between Q_m and d₃₃. Here we report a surprising finding that this tradeoff can be overcome via acceptor-modified invisible-boundary (IB). High Q_m ∼1096 and high d₃₃ ∼337 pC/N were achieved and superior to those of both lead-free and commercial lead-based piezoceramics. The acceptor-modified IB was demonstrated in Fe-doped BaTi_0.89Hf_0.11O₃ ceramics, where the acceptor doping in the IB composition increases Q_m by ∼8.6 times and d₃₃ by ∼1.5 times, being different from the acceptor doping effect in morphotropic/polymorphic phase boundary (MPB/PPB) compositions of increasing Q_m but decreasing d₃₃. We predict that our finding may also be made in other acceptor-modified IB systems and the obtained high-performance BaTiO₃-based piezoceramic could provide an alternative to lead-based piezoceramics in underwater applications.