Hardening of electromechanical properties in piezoceramics using a composite approach

Abstract

Piezoelectric applications such as ultrasonic motors, transformers and therapeutic ultrasonics demand high power generation with low losses, which is facilitated by “hard” ferroelectrics. Hardening of piezoelectric properties, characterized by high mechanical quality factor (Qm), is usually achieved by doping with lower valence elements, thereby tailoring the domain wall dynamics. In the present study, we demonstrate a hardening mechanism by developing composites of 0.94(Na1/2Bi1/2)TiO3-0.06BaTiO3 (NBT-6BT) with ZnO inclusions, as an alternative to chemical modifications. A decrease in the saturation polarization and total strain, higher internal bias fields, lower hysteretic losses and a two-fold increase in Qm are observed in comparison to NBT-6BT. The composite with 0.1 mole ratio of ZnO exhibits the highest Qm of 320 with d33 = 125 pC/N and Kp = 0.29. A one-to-one correspondence between the increase in Qm and the decrease in the domain wall mobility is established from the ac field dependence of permittivity, in the framework of the Rayleigh law. A further increase in ZnO content beyond a mole ratio of 0.1 reduces Qm, but retains it at a higher level, as compared to NBT-6BT. The results are explained based on the poling-induced strain incompatibility between the matrix and the hard ZnO phase. This composite approach is therefore considered a generic hardening concept and can be extended to other ferroelectric systems.

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.…”

“…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].…”

Spontaneous ferroelectric order in lead-free relaxor Na1/2Bi1/2TiVenkataraman1, Hinterstein2, Lee3 et al. 2020Phys. Rev. BSelf Cite15000View full textAdd to dashboardCite

“…However, at 5.5 kV/mm, both samples exhibit intensity changes, indicative of texturing, with the strongest texture observed for NBT9BT. Since texturing directly relates to the domain switching events, the weak texturing in the composite NBT9BT:0.1ZnO is indicative of electromechanical hardening [48].…”

“…The present work facilitates an alternative approach by tailoring the microstructure to spontaneously develop or stabilize the ferroelectric order in relaxor ferroelectrics and is not limited by the nature of the inherent structural disorder present in the system. Apart from providing an extrinsic approach for tailoring the long-range polar order, this approach is beneficial in increasing the thermal stability and hardening of the electromechanical properties [48].…”

Composite microstructures and piezoelectric properties in tantalum substituted lead-free K0.5Na0.5Nb1-xTaxO3 ceramics

“…To our knowledge, such composite structures have not been reported for tantalum doped KNN. In recent literature on KNN and other related lead-free piezoelectric systems [60] the composite approach is one way to provide chemical disorder, structural strains and distortions, or morphotropic phase boundaries. In polycrystalline ceramics, interfaces and grain-tograin interactions can also contribute to modify the movement of the domain walls, with a hardening or softening effect [61].…”