Thermal depolarization and electromechanical hardening in Zn²⁺‐doped Na_1/2Bi_1/2TiO₃‐BaTiO₃

Abstract

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.

Influence of Quenching and Subsequent Annealing on the Conductivity and Electromechanical Properties of Na1/2Bi1/2TiO3-BaTiO3

“…Negligible changes in the mechanical quality factor and coupling coefficient upon quenching was also previously noted for pure NBT [ 18 ]. These results indicate that the electromechanical hardening effects upon quenching is not as pronounced as is the case with ‘hard-type’ NBT-based materials [ 12 , 14 , 22 ]. Nevertheless, this makes quenching a promising approach to tailor material properties beyond the limits of chemical doping.…”

“…Nevertheless, this makes quenching a promising approach to tailor material properties beyond the limits of chemical doping. For example, 0.5 mole% Zn 2+ doping in NBT6BT exhibits a T F-R of 143 °C and mechanical quality factor of 287; quenching 0.5 mole% Zn 2+ doped NBT6BT was demonstrated to increase the T F-R further to 163 °C, while retaining the mechanical quality factor at 280 [ 14 ]. Note that, quenching the doped composition resulted in a significant increase in T F-R beyond the upper limit established by doping (with 1 mole% Zn-doping in NBT6BT, T F-R increases only marginally to 150 °C) [ 14 ].…”

“…In particular, Na 1/2 Bi 1/2 TiO 3 -based materials exhibit superior mechanical [ 11 ] and high power [ 9 ] properties in comparison to the lead-based Pb(Zr,Ti)O 3 . Further, processing strategies such as chemical doping [ 12 , 13 , 14 ], composite formation [ 15 , 16 , 17 ] and quenching [ 18 ] have been demonstrated to significantly alter the conductivity [ 19 ], strain [ 20 ], mechanical quality factor [ 14 , 21 , 22 ] and depolarization temperature [ 14 , 16 , 23 ]. In recent years, quenching from sintering temperature has been adopted as a route to enhance the depolarization temperature (T d ) of Na 1/2 Bi 1/2 TiO 3 (NBT) [ 18 ].…”

Quenching‐circumvented ergodicity in relaxor Na1/2Bi1/2TiO3‐BaTiO3‐K0.5Na0.5NbO3

“…Apart from establishing the practical relevance of the quenching strategy, 21 leveraging an appropriate starting composition (suitably doped, e.g., one with high a mechanical quality factor, Q) could result in further increase in T F-R , beyond that established by the doping limits, with minimal change in the electromechanical response. 16 The stabilized ferroelectric order in quenched NBT necessarily implies changes in the dynamic nature and correlation length of PNRs. However, such a correlation is incomprehensible from investigating non-ergodic relaxors due to the inherent quasi-static nature of PNRs and their increased correlation length.…”

“…16,25 The average structure is then an additional determining factor in stabilizing a relaxor state. Therefore, two different NBT-xBT variants-one with high content of cubic phase at the center of the MPB and another at the edge of the MPB with lower cubic phase content, 16,25 were chosen for the investigation. NBT-xBT-yKNN is reportedly known for its giant strain due to the composition-induced cross over from non-ergodic to ergodic relaxor (>2 mole% KNN), characterized by sproutshaped bipolar strain-field loops in the ergodic state.…”