based materials have been earmarked for one of the first large-volume applications of lead-free piezoceramics in high power ultrasonics. Zn 2+-doping is demonstrated as a viable route to enhance the thermal depolarization temperature and electromechanically harden (1y)Na 1/2 Bi 1/2 TiO 3-yBaTiO 3 (NBT100yBT) with a maximum achievable operating temperature of 150 o C and mechanical quality factor of 627 for 1 mole % Zn 2+-doped NBT6BT. Although quenching from sintering temperatures has been recently touted to enhance T F-R , with quenching Accepted Article This article is protected by copyright. All rights reserved the doped compositions featuring an additional increase of T F-R by 17 o C, it exhibits negligible effect on the electromechanical properties. The effect is rationalized considering the missing influence on conductivity and therefore, negligible changes in the defect chemistry upon quenching. High resolution diffraction indicates that Zn 2+-doped samples favour the tetragonal phase with enhanced lattice distortion, further corroborated by 23 Na Nuclear Magnetic Resonance investigations.